Root/block/cfq-iosched.c

1/*
2 * CFQ, or complete fairness queueing, disk scheduler.
3 *
4 * Based on ideas from a previously unfinished io
5 * scheduler (round robin per-process disk scheduling) and Andrea Arcangeli.
6 *
7 * Copyright (C) 2003 Jens Axboe <axboe@kernel.dk>
8 */
9#include <linux/module.h>
10#include <linux/blkdev.h>
11#include <linux/elevator.h>
12#include <linux/rbtree.h>
13#include <linux/ioprio.h>
14#include <linux/blktrace_api.h>
15
16/*
17 * tunables
18 */
19/* max queue in one round of service */
20static const int cfq_quantum = 4;
21static const int cfq_fifo_expire[2] = { HZ / 4, HZ / 8 };
22/* maximum backwards seek, in KiB */
23static const int cfq_back_max = 16 * 1024;
24/* penalty of a backwards seek */
25static const int cfq_back_penalty = 2;
26static const int cfq_slice_sync = HZ / 10;
27static int cfq_slice_async = HZ / 25;
28static const int cfq_slice_async_rq = 2;
29static int cfq_slice_idle = HZ / 125;
30
31/*
32 * offset from end of service tree
33 */
34#define CFQ_IDLE_DELAY (HZ / 5)
35
36/*
37 * below this threshold, we consider thinktime immediate
38 */
39#define CFQ_MIN_TT (2)
40
41#define CFQ_SLICE_SCALE (5)
42#define CFQ_HW_QUEUE_MIN (5)
43
44#define RQ_CIC(rq) \
45    ((struct cfq_io_context *) (rq)->elevator_private)
46#define RQ_CFQQ(rq) (struct cfq_queue *) ((rq)->elevator_private2)
47
48static struct kmem_cache *cfq_pool;
49static struct kmem_cache *cfq_ioc_pool;
50
51static DEFINE_PER_CPU(unsigned long, cfq_ioc_count);
52static struct completion *ioc_gone;
53static DEFINE_SPINLOCK(ioc_gone_lock);
54
55#define CFQ_PRIO_LISTS IOPRIO_BE_NR
56#define cfq_class_idle(cfqq) ((cfqq)->ioprio_class == IOPRIO_CLASS_IDLE)
57#define cfq_class_rt(cfqq) ((cfqq)->ioprio_class == IOPRIO_CLASS_RT)
58
59#define sample_valid(samples) ((samples) > 80)
60
61/*
62 * Most of our rbtree usage is for sorting with min extraction, so
63 * if we cache the leftmost node we don't have to walk down the tree
64 * to find it. Idea borrowed from Ingo Molnars CFS scheduler. We should
65 * move this into the elevator for the rq sorting as well.
66 */
67struct cfq_rb_root {
68    struct rb_root rb;
69    struct rb_node *left;
70};
71#define CFQ_RB_ROOT (struct cfq_rb_root) { RB_ROOT, NULL, }
72
73/*
74 * Per process-grouping structure
75 */
76struct cfq_queue {
77    /* reference count */
78    atomic_t ref;
79    /* various state flags, see below */
80    unsigned int flags;
81    /* parent cfq_data */
82    struct cfq_data *cfqd;
83    /* service_tree member */
84    struct rb_node rb_node;
85    /* service_tree key */
86    unsigned long rb_key;
87    /* prio tree member */
88    struct rb_node p_node;
89    /* prio tree root we belong to, if any */
90    struct rb_root *p_root;
91    /* sorted list of pending requests */
92    struct rb_root sort_list;
93    /* if fifo isn't expired, next request to serve */
94    struct request *next_rq;
95    /* requests queued in sort_list */
96    int queued[2];
97    /* currently allocated requests */
98    int allocated[2];
99    /* fifo list of requests in sort_list */
100    struct list_head fifo;
101
102    unsigned long slice_end;
103    long slice_resid;
104    unsigned int slice_dispatch;
105
106    /* pending metadata requests */
107    int meta_pending;
108    /* number of requests that are on the dispatch list or inside driver */
109    int dispatched;
110
111    /* io prio of this group */
112    unsigned short ioprio, org_ioprio;
113    unsigned short ioprio_class, org_ioprio_class;
114
115    pid_t pid;
116};
117
118/*
119 * Per block device queue structure
120 */
121struct cfq_data {
122    struct request_queue *queue;
123
124    /*
125     * rr list of queues with requests and the count of them
126     */
127    struct cfq_rb_root service_tree;
128
129    /*
130     * Each priority tree is sorted by next_request position. These
131     * trees are used when determining if two or more queues are
132     * interleaving requests (see cfq_close_cooperator).
133     */
134    struct rb_root prio_trees[CFQ_PRIO_LISTS];
135
136    unsigned int busy_queues;
137
138    int rq_in_driver[2];
139    int sync_flight;
140
141    /*
142     * queue-depth detection
143     */
144    int rq_queued;
145    int hw_tag;
146    int hw_tag_samples;
147    int rq_in_driver_peak;
148
149    /*
150     * idle window management
151     */
152    struct timer_list idle_slice_timer;
153    struct work_struct unplug_work;
154
155    struct cfq_queue *active_queue;
156    struct cfq_io_context *active_cic;
157
158    /*
159     * async queue for each priority case
160     */
161    struct cfq_queue *async_cfqq[2][IOPRIO_BE_NR];
162    struct cfq_queue *async_idle_cfqq;
163
164    sector_t last_position;
165
166    /*
167     * tunables, see top of file
168     */
169    unsigned int cfq_quantum;
170    unsigned int cfq_fifo_expire[2];
171    unsigned int cfq_back_penalty;
172    unsigned int cfq_back_max;
173    unsigned int cfq_slice[2];
174    unsigned int cfq_slice_async_rq;
175    unsigned int cfq_slice_idle;
176    unsigned int cfq_latency;
177
178    struct list_head cic_list;
179
180    /*
181     * Fallback dummy cfqq for extreme OOM conditions
182     */
183    struct cfq_queue oom_cfqq;
184
185    unsigned long last_end_sync_rq;
186};
187
188enum cfqq_state_flags {
189    CFQ_CFQQ_FLAG_on_rr = 0, /* on round-robin busy list */
190    CFQ_CFQQ_FLAG_wait_request, /* waiting for a request */
191    CFQ_CFQQ_FLAG_must_dispatch, /* must be allowed a dispatch */
192    CFQ_CFQQ_FLAG_must_alloc_slice, /* per-slice must_alloc flag */
193    CFQ_CFQQ_FLAG_fifo_expire, /* FIFO checked in this slice */
194    CFQ_CFQQ_FLAG_idle_window, /* slice idling enabled */
195    CFQ_CFQQ_FLAG_prio_changed, /* task priority has changed */
196    CFQ_CFQQ_FLAG_slice_new, /* no requests dispatched in slice */
197    CFQ_CFQQ_FLAG_sync, /* synchronous queue */
198    CFQ_CFQQ_FLAG_coop, /* has done a coop jump of the queue */
199    CFQ_CFQQ_FLAG_coop_preempt, /* coop preempt */
200};
201
202#define CFQ_CFQQ_FNS(name) \
203static inline void cfq_mark_cfqq_##name(struct cfq_queue *cfqq) \
204{ \
205    (cfqq)->flags |= (1 << CFQ_CFQQ_FLAG_##name); \
206} \
207static inline void cfq_clear_cfqq_##name(struct cfq_queue *cfqq) \
208{ \
209    (cfqq)->flags &= ~(1 << CFQ_CFQQ_FLAG_##name); \
210} \
211static inline int cfq_cfqq_##name(const struct cfq_queue *cfqq) \
212{ \
213    return ((cfqq)->flags & (1 << CFQ_CFQQ_FLAG_##name)) != 0; \
214}
215
216CFQ_CFQQ_FNS(on_rr);
217CFQ_CFQQ_FNS(wait_request);
218CFQ_CFQQ_FNS(must_dispatch);
219CFQ_CFQQ_FNS(must_alloc_slice);
220CFQ_CFQQ_FNS(fifo_expire);
221CFQ_CFQQ_FNS(idle_window);
222CFQ_CFQQ_FNS(prio_changed);
223CFQ_CFQQ_FNS(slice_new);
224CFQ_CFQQ_FNS(sync);
225CFQ_CFQQ_FNS(coop);
226CFQ_CFQQ_FNS(coop_preempt);
227#undef CFQ_CFQQ_FNS
228
229#define cfq_log_cfqq(cfqd, cfqq, fmt, args...) \
230    blk_add_trace_msg((cfqd)->queue, "cfq%d " fmt, (cfqq)->pid, ##args)
231#define cfq_log(cfqd, fmt, args...) \
232    blk_add_trace_msg((cfqd)->queue, "cfq " fmt, ##args)
233
234static void cfq_dispatch_insert(struct request_queue *, struct request *);
235static struct cfq_queue *cfq_get_queue(struct cfq_data *, bool,
236                       struct io_context *, gfp_t);
237static struct cfq_io_context *cfq_cic_lookup(struct cfq_data *,
238                        struct io_context *);
239
240static inline int rq_in_driver(struct cfq_data *cfqd)
241{
242    return cfqd->rq_in_driver[0] + cfqd->rq_in_driver[1];
243}
244
245static inline struct cfq_queue *cic_to_cfqq(struct cfq_io_context *cic,
246                        bool is_sync)
247{
248    return cic->cfqq[is_sync];
249}
250
251static inline void cic_set_cfqq(struct cfq_io_context *cic,
252                struct cfq_queue *cfqq, bool is_sync)
253{
254    cic->cfqq[is_sync] = cfqq;
255}
256
257/*
258 * We regard a request as SYNC, if it's either a read or has the SYNC bit
259 * set (in which case it could also be direct WRITE).
260 */
261static inline bool cfq_bio_sync(struct bio *bio)
262{
263    return bio_data_dir(bio) == READ || bio_rw_flagged(bio, BIO_RW_SYNCIO);
264}
265
266/*
267 * scheduler run of queue, if there are requests pending and no one in the
268 * driver that will restart queueing
269 */
270static inline void cfq_schedule_dispatch(struct cfq_data *cfqd)
271{
272    if (cfqd->busy_queues) {
273        cfq_log(cfqd, "schedule dispatch");
274        kblockd_schedule_work(cfqd->queue, &cfqd->unplug_work);
275    }
276}
277
278static int cfq_queue_empty(struct request_queue *q)
279{
280    struct cfq_data *cfqd = q->elevator->elevator_data;
281
282    return !cfqd->busy_queues;
283}
284
285/*
286 * Scale schedule slice based on io priority. Use the sync time slice only
287 * if a queue is marked sync and has sync io queued. A sync queue with async
288 * io only, should not get full sync slice length.
289 */
290static inline int cfq_prio_slice(struct cfq_data *cfqd, bool sync,
291                 unsigned short prio)
292{
293    const int base_slice = cfqd->cfq_slice[sync];
294
295    WARN_ON(prio >= IOPRIO_BE_NR);
296
297    return base_slice + (base_slice/CFQ_SLICE_SCALE * (4 - prio));
298}
299
300static inline int
301cfq_prio_to_slice(struct cfq_data *cfqd, struct cfq_queue *cfqq)
302{
303    return cfq_prio_slice(cfqd, cfq_cfqq_sync(cfqq), cfqq->ioprio);
304}
305
306static inline void
307cfq_set_prio_slice(struct cfq_data *cfqd, struct cfq_queue *cfqq)
308{
309    cfqq->slice_end = cfq_prio_to_slice(cfqd, cfqq) + jiffies;
310    cfq_log_cfqq(cfqd, cfqq, "set_slice=%lu", cfqq->slice_end - jiffies);
311}
312
313/*
314 * We need to wrap this check in cfq_cfqq_slice_new(), since ->slice_end
315 * isn't valid until the first request from the dispatch is activated
316 * and the slice time set.
317 */
318static inline bool cfq_slice_used(struct cfq_queue *cfqq)
319{
320    if (cfq_cfqq_slice_new(cfqq))
321        return 0;
322    if (time_before(jiffies, cfqq->slice_end))
323        return 0;
324
325    return 1;
326}
327
328/*
329 * Lifted from AS - choose which of rq1 and rq2 that is best served now.
330 * We choose the request that is closest to the head right now. Distance
331 * behind the head is penalized and only allowed to a certain extent.
332 */
333static struct request *
334cfq_choose_req(struct cfq_data *cfqd, struct request *rq1, struct request *rq2)
335{
336    sector_t last, s1, s2, d1 = 0, d2 = 0;
337    unsigned long back_max;
338#define CFQ_RQ1_WRAP 0x01 /* request 1 wraps */
339#define CFQ_RQ2_WRAP 0x02 /* request 2 wraps */
340    unsigned wrap = 0; /* bit mask: requests behind the disk head? */
341
342    if (rq1 == NULL || rq1 == rq2)
343        return rq2;
344    if (rq2 == NULL)
345        return rq1;
346
347    if (rq_is_sync(rq1) && !rq_is_sync(rq2))
348        return rq1;
349    else if (rq_is_sync(rq2) && !rq_is_sync(rq1))
350        return rq2;
351    if (rq_is_meta(rq1) && !rq_is_meta(rq2))
352        return rq1;
353    else if (rq_is_meta(rq2) && !rq_is_meta(rq1))
354        return rq2;
355
356    s1 = blk_rq_pos(rq1);
357    s2 = blk_rq_pos(rq2);
358
359    last = cfqd->last_position;
360
361    /*
362     * by definition, 1KiB is 2 sectors
363     */
364    back_max = cfqd->cfq_back_max * 2;
365
366    /*
367     * Strict one way elevator _except_ in the case where we allow
368     * short backward seeks which are biased as twice the cost of a
369     * similar forward seek.
370     */
371    if (s1 >= last)
372        d1 = s1 - last;
373    else if (s1 + back_max >= last)
374        d1 = (last - s1) * cfqd->cfq_back_penalty;
375    else
376        wrap |= CFQ_RQ1_WRAP;
377
378    if (s2 >= last)
379        d2 = s2 - last;
380    else if (s2 + back_max >= last)
381        d2 = (last - s2) * cfqd->cfq_back_penalty;
382    else
383        wrap |= CFQ_RQ2_WRAP;
384
385    /* Found required data */
386
387    /*
388     * By doing switch() on the bit mask "wrap" we avoid having to
389     * check two variables for all permutations: --> faster!
390     */
391    switch (wrap) {
392    case 0: /* common case for CFQ: rq1 and rq2 not wrapped */
393        if (d1 < d2)
394            return rq1;
395        else if (d2 < d1)
396            return rq2;
397        else {
398            if (s1 >= s2)
399                return rq1;
400            else
401                return rq2;
402        }
403
404    case CFQ_RQ2_WRAP:
405        return rq1;
406    case CFQ_RQ1_WRAP:
407        return rq2;
408    case (CFQ_RQ1_WRAP|CFQ_RQ2_WRAP): /* both rqs wrapped */
409    default:
410        /*
411         * Since both rqs are wrapped,
412         * start with the one that's further behind head
413         * (--> only *one* back seek required),
414         * since back seek takes more time than forward.
415         */
416        if (s1 <= s2)
417            return rq1;
418        else
419            return rq2;
420    }
421}
422
423/*
424 * The below is leftmost cache rbtree addon
425 */
426static struct cfq_queue *cfq_rb_first(struct cfq_rb_root *root)
427{
428    if (!root->left)
429        root->left = rb_first(&root->rb);
430
431    if (root->left)
432        return rb_entry(root->left, struct cfq_queue, rb_node);
433
434    return NULL;
435}
436
437static void rb_erase_init(struct rb_node *n, struct rb_root *root)
438{
439    rb_erase(n, root);
440    RB_CLEAR_NODE(n);
441}
442
443static void cfq_rb_erase(struct rb_node *n, struct cfq_rb_root *root)
444{
445    if (root->left == n)
446        root->left = NULL;
447    rb_erase_init(n, &root->rb);
448}
449
450/*
451 * would be nice to take fifo expire time into account as well
452 */
453static struct request *
454cfq_find_next_rq(struct cfq_data *cfqd, struct cfq_queue *cfqq,
455          struct request *last)
456{
457    struct rb_node *rbnext = rb_next(&last->rb_node);
458    struct rb_node *rbprev = rb_prev(&last->rb_node);
459    struct request *next = NULL, *prev = NULL;
460
461    BUG_ON(RB_EMPTY_NODE(&last->rb_node));
462
463    if (rbprev)
464        prev = rb_entry_rq(rbprev);
465
466    if (rbnext)
467        next = rb_entry_rq(rbnext);
468    else {
469        rbnext = rb_first(&cfqq->sort_list);
470        if (rbnext && rbnext != &last->rb_node)
471            next = rb_entry_rq(rbnext);
472    }
473
474    return cfq_choose_req(cfqd, next, prev);
475}
476
477static unsigned long cfq_slice_offset(struct cfq_data *cfqd,
478                      struct cfq_queue *cfqq)
479{
480    /*
481     * just an approximation, should be ok.
482     */
483    return (cfqd->busy_queues - 1) * (cfq_prio_slice(cfqd, 1, 0) -
484               cfq_prio_slice(cfqd, cfq_cfqq_sync(cfqq), cfqq->ioprio));
485}
486
487/*
488 * The cfqd->service_tree holds all pending cfq_queue's that have
489 * requests waiting to be processed. It is sorted in the order that
490 * we will service the queues.
491 */
492static void cfq_service_tree_add(struct cfq_data *cfqd, struct cfq_queue *cfqq,
493                 bool add_front)
494{
495    struct rb_node **p, *parent;
496    struct cfq_queue *__cfqq;
497    unsigned long rb_key;
498    int left;
499
500    if (cfq_class_idle(cfqq)) {
501        rb_key = CFQ_IDLE_DELAY;
502        parent = rb_last(&cfqd->service_tree.rb);
503        if (parent && parent != &cfqq->rb_node) {
504            __cfqq = rb_entry(parent, struct cfq_queue, rb_node);
505            rb_key += __cfqq->rb_key;
506        } else
507            rb_key += jiffies;
508    } else if (!add_front) {
509        /*
510         * Get our rb key offset. Subtract any residual slice
511         * value carried from last service. A negative resid
512         * count indicates slice overrun, and this should position
513         * the next service time further away in the tree.
514         */
515        rb_key = cfq_slice_offset(cfqd, cfqq) + jiffies;
516        rb_key -= cfqq->slice_resid;
517        cfqq->slice_resid = 0;
518    } else {
519        rb_key = -HZ;
520        __cfqq = cfq_rb_first(&cfqd->service_tree);
521        rb_key += __cfqq ? __cfqq->rb_key : jiffies;
522    }
523
524    if (!RB_EMPTY_NODE(&cfqq->rb_node)) {
525        /*
526         * same position, nothing more to do
527         */
528        if (rb_key == cfqq->rb_key)
529            return;
530
531        cfq_rb_erase(&cfqq->rb_node, &cfqd->service_tree);
532    }
533
534    left = 1;
535    parent = NULL;
536    p = &cfqd->service_tree.rb.rb_node;
537    while (*p) {
538        struct rb_node **n;
539
540        parent = *p;
541        __cfqq = rb_entry(parent, struct cfq_queue, rb_node);
542
543        /*
544         * sort RT queues first, we always want to give
545         * preference to them. IDLE queues goes to the back.
546         * after that, sort on the next service time.
547         */
548        if (cfq_class_rt(cfqq) > cfq_class_rt(__cfqq))
549            n = &(*p)->rb_left;
550        else if (cfq_class_rt(cfqq) < cfq_class_rt(__cfqq))
551            n = &(*p)->rb_right;
552        else if (cfq_class_idle(cfqq) < cfq_class_idle(__cfqq))
553            n = &(*p)->rb_left;
554        else if (cfq_class_idle(cfqq) > cfq_class_idle(__cfqq))
555            n = &(*p)->rb_right;
556        else if (time_before(rb_key, __cfqq->rb_key))
557            n = &(*p)->rb_left;
558        else
559            n = &(*p)->rb_right;
560
561        if (n == &(*p)->rb_right)
562            left = 0;
563
564        p = n;
565    }
566
567    if (left)
568        cfqd->service_tree.left = &cfqq->rb_node;
569
570    cfqq->rb_key = rb_key;
571    rb_link_node(&cfqq->rb_node, parent, p);
572    rb_insert_color(&cfqq->rb_node, &cfqd->service_tree.rb);
573}
574
575static struct cfq_queue *
576cfq_prio_tree_lookup(struct cfq_data *cfqd, struct rb_root *root,
577             sector_t sector, struct rb_node **ret_parent,
578             struct rb_node ***rb_link)
579{
580    struct rb_node **p, *parent;
581    struct cfq_queue *cfqq = NULL;
582
583    parent = NULL;
584    p = &root->rb_node;
585    while (*p) {
586        struct rb_node **n;
587
588        parent = *p;
589        cfqq = rb_entry(parent, struct cfq_queue, p_node);
590
591        /*
592         * Sort strictly based on sector. Smallest to the left,
593         * largest to the right.
594         */
595        if (sector > blk_rq_pos(cfqq->next_rq))
596            n = &(*p)->rb_right;
597        else if (sector < blk_rq_pos(cfqq->next_rq))
598            n = &(*p)->rb_left;
599        else
600            break;
601        p = n;
602        cfqq = NULL;
603    }
604
605    *ret_parent = parent;
606    if (rb_link)
607        *rb_link = p;
608    return cfqq;
609}
610
611static void cfq_prio_tree_add(struct cfq_data *cfqd, struct cfq_queue *cfqq)
612{
613    struct rb_node **p, *parent;
614    struct cfq_queue *__cfqq;
615
616    if (cfqq->p_root) {
617        rb_erase(&cfqq->p_node, cfqq->p_root);
618        cfqq->p_root = NULL;
619    }
620
621    if (cfq_class_idle(cfqq))
622        return;
623    if (!cfqq->next_rq)
624        return;
625
626    cfqq->p_root = &cfqd->prio_trees[cfqq->org_ioprio];
627    __cfqq = cfq_prio_tree_lookup(cfqd, cfqq->p_root,
628                      blk_rq_pos(cfqq->next_rq), &parent, &p);
629    if (!__cfqq) {
630        rb_link_node(&cfqq->p_node, parent, p);
631        rb_insert_color(&cfqq->p_node, cfqq->p_root);
632    } else
633        cfqq->p_root = NULL;
634}
635
636/*
637 * Update cfqq's position in the service tree.
638 */
639static void cfq_resort_rr_list(struct cfq_data *cfqd, struct cfq_queue *cfqq)
640{
641    /*
642     * Resorting requires the cfqq to be on the RR list already.
643     */
644    if (cfq_cfqq_on_rr(cfqq)) {
645        cfq_service_tree_add(cfqd, cfqq, 0);
646        cfq_prio_tree_add(cfqd, cfqq);
647    }
648}
649
650/*
651 * add to busy list of queues for service, trying to be fair in ordering
652 * the pending list according to last request service
653 */
654static void cfq_add_cfqq_rr(struct cfq_data *cfqd, struct cfq_queue *cfqq)
655{
656    cfq_log_cfqq(cfqd, cfqq, "add_to_rr");
657    BUG_ON(cfq_cfqq_on_rr(cfqq));
658    cfq_mark_cfqq_on_rr(cfqq);
659    cfqd->busy_queues++;
660
661    cfq_resort_rr_list(cfqd, cfqq);
662}
663
664/*
665 * Called when the cfqq no longer has requests pending, remove it from
666 * the service tree.
667 */
668static void cfq_del_cfqq_rr(struct cfq_data *cfqd, struct cfq_queue *cfqq)
669{
670    cfq_log_cfqq(cfqd, cfqq, "del_from_rr");
671    BUG_ON(!cfq_cfqq_on_rr(cfqq));
672    cfq_clear_cfqq_on_rr(cfqq);
673
674    if (!RB_EMPTY_NODE(&cfqq->rb_node))
675        cfq_rb_erase(&cfqq->rb_node, &cfqd->service_tree);
676    if (cfqq->p_root) {
677        rb_erase(&cfqq->p_node, cfqq->p_root);
678        cfqq->p_root = NULL;
679    }
680
681    BUG_ON(!cfqd->busy_queues);
682    cfqd->busy_queues--;
683}
684
685/*
686 * rb tree support functions
687 */
688static void cfq_del_rq_rb(struct request *rq)
689{
690    struct cfq_queue *cfqq = RQ_CFQQ(rq);
691    struct cfq_data *cfqd = cfqq->cfqd;
692    const int sync = rq_is_sync(rq);
693
694    BUG_ON(!cfqq->queued[sync]);
695    cfqq->queued[sync]--;
696
697    elv_rb_del(&cfqq->sort_list, rq);
698
699    if (cfq_cfqq_on_rr(cfqq) && RB_EMPTY_ROOT(&cfqq->sort_list))
700        cfq_del_cfqq_rr(cfqd, cfqq);
701}
702
703static void cfq_add_rq_rb(struct request *rq)
704{
705    struct cfq_queue *cfqq = RQ_CFQQ(rq);
706    struct cfq_data *cfqd = cfqq->cfqd;
707    struct request *__alias, *prev;
708
709    cfqq->queued[rq_is_sync(rq)]++;
710
711    /*
712     * looks a little odd, but the first insert might return an alias.
713     * if that happens, put the alias on the dispatch list
714     */
715    while ((__alias = elv_rb_add(&cfqq->sort_list, rq)) != NULL)
716        cfq_dispatch_insert(cfqd->queue, __alias);
717
718    if (!cfq_cfqq_on_rr(cfqq))
719        cfq_add_cfqq_rr(cfqd, cfqq);
720
721    /*
722     * check if this request is a better next-serve candidate
723     */
724    prev = cfqq->next_rq;
725    cfqq->next_rq = cfq_choose_req(cfqd, cfqq->next_rq, rq);
726
727    /*
728     * adjust priority tree position, if ->next_rq changes
729     */
730    if (prev != cfqq->next_rq)
731        cfq_prio_tree_add(cfqd, cfqq);
732
733    BUG_ON(!cfqq->next_rq);
734}
735
736static void cfq_reposition_rq_rb(struct cfq_queue *cfqq, struct request *rq)
737{
738    elv_rb_del(&cfqq->sort_list, rq);
739    cfqq->queued[rq_is_sync(rq)]--;
740    cfq_add_rq_rb(rq);
741}
742
743static struct request *
744cfq_find_rq_fmerge(struct cfq_data *cfqd, struct bio *bio)
745{
746    struct task_struct *tsk = current;
747    struct cfq_io_context *cic;
748    struct cfq_queue *cfqq;
749
750    cic = cfq_cic_lookup(cfqd, tsk->io_context);
751    if (!cic)
752        return NULL;
753
754    cfqq = cic_to_cfqq(cic, cfq_bio_sync(bio));
755    if (cfqq) {
756        sector_t sector = bio->bi_sector + bio_sectors(bio);
757
758        return elv_rb_find(&cfqq->sort_list, sector);
759    }
760
761    return NULL;
762}
763
764static void cfq_activate_request(struct request_queue *q, struct request *rq)
765{
766    struct cfq_data *cfqd = q->elevator->elevator_data;
767
768    cfqd->rq_in_driver[rq_is_sync(rq)]++;
769    cfq_log_cfqq(cfqd, RQ_CFQQ(rq), "activate rq, drv=%d",
770                        rq_in_driver(cfqd));
771
772    cfqd->last_position = blk_rq_pos(rq) + blk_rq_sectors(rq);
773}
774
775static void cfq_deactivate_request(struct request_queue *q, struct request *rq)
776{
777    struct cfq_data *cfqd = q->elevator->elevator_data;
778    const int sync = rq_is_sync(rq);
779
780    WARN_ON(!cfqd->rq_in_driver[sync]);
781    cfqd->rq_in_driver[sync]--;
782    cfq_log_cfqq(cfqd, RQ_CFQQ(rq), "deactivate rq, drv=%d",
783                        rq_in_driver(cfqd));
784}
785
786static void cfq_remove_request(struct request *rq)
787{
788    struct cfq_queue *cfqq = RQ_CFQQ(rq);
789
790    if (cfqq->next_rq == rq)
791        cfqq->next_rq = cfq_find_next_rq(cfqq->cfqd, cfqq, rq);
792
793    list_del_init(&rq->queuelist);
794    cfq_del_rq_rb(rq);
795
796    cfqq->cfqd->rq_queued--;
797    if (rq_is_meta(rq)) {
798        WARN_ON(!cfqq->meta_pending);
799        cfqq->meta_pending--;
800    }
801}
802
803static int cfq_merge(struct request_queue *q, struct request **req,
804             struct bio *bio)
805{
806    struct cfq_data *cfqd = q->elevator->elevator_data;
807    struct request *__rq;
808
809    __rq = cfq_find_rq_fmerge(cfqd, bio);
810    if (__rq && elv_rq_merge_ok(__rq, bio)) {
811        *req = __rq;
812        return ELEVATOR_FRONT_MERGE;
813    }
814
815    return ELEVATOR_NO_MERGE;
816}
817
818static void cfq_merged_request(struct request_queue *q, struct request *req,
819                   int type)
820{
821    if (type == ELEVATOR_FRONT_MERGE) {
822        struct cfq_queue *cfqq = RQ_CFQQ(req);
823
824        cfq_reposition_rq_rb(cfqq, req);
825    }
826}
827
828static void
829cfq_merged_requests(struct request_queue *q, struct request *rq,
830            struct request *next)
831{
832    /*
833     * reposition in fifo if next is older than rq
834     */
835    if (!list_empty(&rq->queuelist) && !list_empty(&next->queuelist) &&
836        time_before(rq_fifo_time(next), rq_fifo_time(rq))) {
837        list_move(&rq->queuelist, &next->queuelist);
838        rq_set_fifo_time(rq, rq_fifo_time(next));
839    }
840
841    cfq_remove_request(next);
842}
843
844static int cfq_allow_merge(struct request_queue *q, struct request *rq,
845               struct bio *bio)
846{
847    struct cfq_data *cfqd = q->elevator->elevator_data;
848    struct cfq_io_context *cic;
849    struct cfq_queue *cfqq;
850
851    /*
852     * Disallow merge of a sync bio into an async request.
853     */
854    if (cfq_bio_sync(bio) && !rq_is_sync(rq))
855        return false;
856
857    /*
858     * Lookup the cfqq that this bio will be queued with. Allow
859     * merge only if rq is queued there.
860     */
861    cic = cfq_cic_lookup(cfqd, current->io_context);
862    if (!cic)
863        return false;
864
865    cfqq = cic_to_cfqq(cic, cfq_bio_sync(bio));
866    return cfqq == RQ_CFQQ(rq);
867}
868
869static void __cfq_set_active_queue(struct cfq_data *cfqd,
870                   struct cfq_queue *cfqq)
871{
872    if (cfqq) {
873        cfq_log_cfqq(cfqd, cfqq, "set_active");
874        cfqq->slice_end = 0;
875        cfqq->slice_dispatch = 0;
876
877        cfq_clear_cfqq_wait_request(cfqq);
878        cfq_clear_cfqq_must_dispatch(cfqq);
879        cfq_clear_cfqq_must_alloc_slice(cfqq);
880        cfq_clear_cfqq_fifo_expire(cfqq);
881        cfq_mark_cfqq_slice_new(cfqq);
882
883        del_timer(&cfqd->idle_slice_timer);
884    }
885
886    cfqd->active_queue = cfqq;
887}
888
889/*
890 * current cfqq expired its slice (or was too idle), select new one
891 */
892static void
893__cfq_slice_expired(struct cfq_data *cfqd, struct cfq_queue *cfqq,
894            bool timed_out)
895{
896    cfq_log_cfqq(cfqd, cfqq, "slice expired t=%d", timed_out);
897
898    if (cfq_cfqq_wait_request(cfqq))
899        del_timer(&cfqd->idle_slice_timer);
900
901    cfq_clear_cfqq_wait_request(cfqq);
902
903    /*
904     * store what was left of this slice, if the queue idled/timed out
905     */
906    if (timed_out && !cfq_cfqq_slice_new(cfqq)) {
907        cfqq->slice_resid = cfqq->slice_end - jiffies;
908        cfq_log_cfqq(cfqd, cfqq, "resid=%ld", cfqq->slice_resid);
909    }
910
911    cfq_resort_rr_list(cfqd, cfqq);
912
913    if (cfqq == cfqd->active_queue)
914        cfqd->active_queue = NULL;
915
916    if (cfqd->active_cic) {
917        put_io_context(cfqd->active_cic->ioc);
918        cfqd->active_cic = NULL;
919    }
920}
921
922static inline void cfq_slice_expired(struct cfq_data *cfqd, bool timed_out)
923{
924    struct cfq_queue *cfqq = cfqd->active_queue;
925
926    if (cfqq)
927        __cfq_slice_expired(cfqd, cfqq, timed_out);
928}
929
930/*
931 * Get next queue for service. Unless we have a queue preemption,
932 * we'll simply select the first cfqq in the service tree.
933 */
934static struct cfq_queue *cfq_get_next_queue(struct cfq_data *cfqd)
935{
936    if (RB_EMPTY_ROOT(&cfqd->service_tree.rb))
937        return NULL;
938
939    return cfq_rb_first(&cfqd->service_tree);
940}
941
942/*
943 * Get and set a new active queue for service.
944 */
945static struct cfq_queue *cfq_set_active_queue(struct cfq_data *cfqd,
946                          struct cfq_queue *cfqq)
947{
948    if (!cfqq) {
949        cfqq = cfq_get_next_queue(cfqd);
950        if (cfqq && !cfq_cfqq_coop_preempt(cfqq))
951            cfq_clear_cfqq_coop(cfqq);
952    }
953
954    if (cfqq)
955        cfq_clear_cfqq_coop_preempt(cfqq);
956
957    __cfq_set_active_queue(cfqd, cfqq);
958    return cfqq;
959}
960
961static inline sector_t cfq_dist_from_last(struct cfq_data *cfqd,
962                      struct request *rq)
963{
964    if (blk_rq_pos(rq) >= cfqd->last_position)
965        return blk_rq_pos(rq) - cfqd->last_position;
966    else
967        return cfqd->last_position - blk_rq_pos(rq);
968}
969
970#define CIC_SEEK_THR 8 * 1024
971#define CIC_SEEKY(cic) ((cic)->seek_mean > CIC_SEEK_THR)
972
973static inline int cfq_rq_close(struct cfq_data *cfqd, struct request *rq)
974{
975    struct cfq_io_context *cic = cfqd->active_cic;
976    sector_t sdist = cic->seek_mean;
977
978    if (!sample_valid(cic->seek_samples))
979        sdist = CIC_SEEK_THR;
980
981    return cfq_dist_from_last(cfqd, rq) <= sdist;
982}
983
984static struct cfq_queue *cfqq_close(struct cfq_data *cfqd,
985                    struct cfq_queue *cur_cfqq)
986{
987    struct rb_root *root = &cfqd->prio_trees[cur_cfqq->org_ioprio];
988    struct rb_node *parent, *node;
989    struct cfq_queue *__cfqq;
990    sector_t sector = cfqd->last_position;
991
992    if (RB_EMPTY_ROOT(root))
993        return NULL;
994
995    /*
996     * First, if we find a request starting at the end of the last
997     * request, choose it.
998     */
999    __cfqq = cfq_prio_tree_lookup(cfqd, root, sector, &parent, NULL);
1000    if (__cfqq)
1001        return __cfqq;
1002
1003    /*
1004     * If the exact sector wasn't found, the parent of the NULL leaf
1005     * will contain the closest sector.
1006     */
1007    __cfqq = rb_entry(parent, struct cfq_queue, p_node);
1008    if (cfq_rq_close(cfqd, __cfqq->next_rq))
1009        return __cfqq;
1010
1011    if (blk_rq_pos(__cfqq->next_rq) < sector)
1012        node = rb_next(&__cfqq->p_node);
1013    else
1014        node = rb_prev(&__cfqq->p_node);
1015    if (!node)
1016        return NULL;
1017
1018    __cfqq = rb_entry(node, struct cfq_queue, p_node);
1019    if (cfq_rq_close(cfqd, __cfqq->next_rq))
1020        return __cfqq;
1021
1022    return NULL;
1023}
1024
1025/*
1026 * cfqd - obvious
1027 * cur_cfqq - passed in so that we don't decide that the current queue is
1028 * closely cooperating with itself.
1029 *
1030 * So, basically we're assuming that that cur_cfqq has dispatched at least
1031 * one request, and that cfqd->last_position reflects a position on the disk
1032 * associated with the I/O issued by cur_cfqq. I'm not sure this is a valid
1033 * assumption.
1034 */
1035static struct cfq_queue *cfq_close_cooperator(struct cfq_data *cfqd,
1036                          struct cfq_queue *cur_cfqq,
1037                          bool probe)
1038{
1039    struct cfq_queue *cfqq;
1040
1041    /*
1042     * A valid cfq_io_context is necessary to compare requests against
1043     * the seek_mean of the current cfqq.
1044     */
1045    if (!cfqd->active_cic)
1046        return NULL;
1047
1048    /*
1049     * We should notice if some of the queues are cooperating, eg
1050     * working closely on the same area of the disk. In that case,
1051     * we can group them together and don't waste time idling.
1052     */
1053    cfqq = cfqq_close(cfqd, cur_cfqq);
1054    if (!cfqq)
1055        return NULL;
1056
1057    if (cfq_cfqq_coop(cfqq))
1058        return NULL;
1059
1060    if (!probe)
1061        cfq_mark_cfqq_coop(cfqq);
1062    return cfqq;
1063}
1064
1065static void cfq_arm_slice_timer(struct cfq_data *cfqd)
1066{
1067    struct cfq_queue *cfqq = cfqd->active_queue;
1068    struct cfq_io_context *cic;
1069    unsigned long sl;
1070
1071    /*
1072     * SSD device without seek penalty, disable idling. But only do so
1073     * for devices that support queuing, otherwise we still have a problem
1074     * with sync vs async workloads.
1075     */
1076    if (blk_queue_nonrot(cfqd->queue) && cfqd->hw_tag)
1077        return;
1078
1079    WARN_ON(!RB_EMPTY_ROOT(&cfqq->sort_list));
1080    WARN_ON(cfq_cfqq_slice_new(cfqq));
1081
1082    /*
1083     * idle is disabled, either manually or by past process history
1084     */
1085    if (!cfqd->cfq_slice_idle || !cfq_cfqq_idle_window(cfqq))
1086        return;
1087
1088    /*
1089     * still requests with the driver, don't idle
1090     */
1091    if (rq_in_driver(cfqd))
1092        return;
1093
1094    /*
1095     * task has exited, don't wait
1096     */
1097    cic = cfqd->active_cic;
1098    if (!cic || !atomic_read(&cic->ioc->nr_tasks))
1099        return;
1100
1101    /*
1102     * If our average think time is larger than the remaining time
1103     * slice, then don't idle. This avoids overrunning the allotted
1104     * time slice.
1105     */
1106    if (sample_valid(cic->ttime_samples) &&
1107        (cfqq->slice_end - jiffies < cic->ttime_mean))
1108        return;
1109
1110    cfq_mark_cfqq_wait_request(cfqq);
1111
1112    /*
1113     * we don't want to idle for seeks, but we do want to allow
1114     * fair distribution of slice time for a process doing back-to-back
1115     * seeks. so allow a little bit of time for him to submit a new rq
1116     */
1117    sl = cfqd->cfq_slice_idle;
1118    if (sample_valid(cic->seek_samples) && CIC_SEEKY(cic))
1119        sl = min(sl, msecs_to_jiffies(CFQ_MIN_TT));
1120
1121    mod_timer(&cfqd->idle_slice_timer, jiffies + sl);
1122    cfq_log_cfqq(cfqd, cfqq, "arm_idle: %lu", sl);
1123}
1124
1125/*
1126 * Move request from internal lists to the request queue dispatch list.
1127 */
1128static void cfq_dispatch_insert(struct request_queue *q, struct request *rq)
1129{
1130    struct cfq_data *cfqd = q->elevator->elevator_data;
1131    struct cfq_queue *cfqq = RQ_CFQQ(rq);
1132
1133    cfq_log_cfqq(cfqd, cfqq, "dispatch_insert");
1134
1135    cfqq->next_rq = cfq_find_next_rq(cfqd, cfqq, rq);
1136    cfq_remove_request(rq);
1137    cfqq->dispatched++;
1138    elv_dispatch_sort(q, rq);
1139
1140    if (cfq_cfqq_sync(cfqq))
1141        cfqd->sync_flight++;
1142}
1143
1144/*
1145 * return expired entry, or NULL to just start from scratch in rbtree
1146 */
1147static struct request *cfq_check_fifo(struct cfq_queue *cfqq)
1148{
1149    struct request *rq = NULL;
1150
1151    if (cfq_cfqq_fifo_expire(cfqq))
1152        return NULL;
1153
1154    cfq_mark_cfqq_fifo_expire(cfqq);
1155
1156    if (list_empty(&cfqq->fifo))
1157        return NULL;
1158
1159    rq = rq_entry_fifo(cfqq->fifo.next);
1160    if (time_before(jiffies, rq_fifo_time(rq)))
1161        rq = NULL;
1162
1163    cfq_log_cfqq(cfqq->cfqd, cfqq, "fifo=%p", rq);
1164    return rq;
1165}
1166
1167static inline int
1168cfq_prio_to_maxrq(struct cfq_data *cfqd, struct cfq_queue *cfqq)
1169{
1170    const int base_rq = cfqd->cfq_slice_async_rq;
1171
1172    WARN_ON(cfqq->ioprio >= IOPRIO_BE_NR);
1173
1174    return 2 * (base_rq + base_rq * (CFQ_PRIO_LISTS - 1 - cfqq->ioprio));
1175}
1176
1177/*
1178 * Select a queue for service. If we have a current active queue,
1179 * check whether to continue servicing it, or retrieve and set a new one.
1180 */
1181static struct cfq_queue *cfq_select_queue(struct cfq_data *cfqd)
1182{
1183    struct cfq_queue *cfqq, *new_cfqq = NULL;
1184
1185    cfqq = cfqd->active_queue;
1186    if (!cfqq)
1187        goto new_queue;
1188
1189    /*
1190     * The active queue has run out of time, expire it and select new.
1191     */
1192    if (cfq_slice_used(cfqq) && !cfq_cfqq_must_dispatch(cfqq))
1193        goto expire;
1194
1195    /*
1196     * The active queue has requests and isn't expired, allow it to
1197     * dispatch.
1198     */
1199    if (!RB_EMPTY_ROOT(&cfqq->sort_list))
1200        goto keep_queue;
1201
1202    /*
1203     * If another queue has a request waiting within our mean seek
1204     * distance, let it run. The expire code will check for close
1205     * cooperators and put the close queue at the front of the service
1206     * tree.
1207     */
1208    new_cfqq = cfq_close_cooperator(cfqd, cfqq, 0);
1209    if (new_cfqq)
1210        goto expire;
1211
1212    /*
1213     * No requests pending. If the active queue still has requests in
1214     * flight or is idling for a new request, allow either of these
1215     * conditions to happen (or time out) before selecting a new queue.
1216     */
1217    if (timer_pending(&cfqd->idle_slice_timer) ||
1218        (cfqq->dispatched && cfq_cfqq_idle_window(cfqq))) {
1219        cfqq = NULL;
1220        goto keep_queue;
1221    }
1222
1223expire:
1224    cfq_slice_expired(cfqd, 0);
1225new_queue:
1226    cfqq = cfq_set_active_queue(cfqd, new_cfqq);
1227keep_queue:
1228    return cfqq;
1229}
1230
1231static int __cfq_forced_dispatch_cfqq(struct cfq_queue *cfqq)
1232{
1233    int dispatched = 0;
1234
1235    while (cfqq->next_rq) {
1236        cfq_dispatch_insert(cfqq->cfqd->queue, cfqq->next_rq);
1237        dispatched++;
1238    }
1239
1240    BUG_ON(!list_empty(&cfqq->fifo));
1241    return dispatched;
1242}
1243
1244/*
1245 * Drain our current requests. Used for barriers and when switching
1246 * io schedulers on-the-fly.
1247 */
1248static int cfq_forced_dispatch(struct cfq_data *cfqd)
1249{
1250    struct cfq_queue *cfqq;
1251    int dispatched = 0;
1252
1253    while ((cfqq = cfq_rb_first(&cfqd->service_tree)) != NULL)
1254        dispatched += __cfq_forced_dispatch_cfqq(cfqq);
1255
1256    cfq_slice_expired(cfqd, 0);
1257
1258    BUG_ON(cfqd->busy_queues);
1259
1260    cfq_log(cfqd, "forced_dispatch=%d", dispatched);
1261    return dispatched;
1262}
1263
1264static bool cfq_may_dispatch(struct cfq_data *cfqd, struct cfq_queue *cfqq)
1265{
1266    unsigned int max_dispatch;
1267
1268    /*
1269     * Drain async requests before we start sync IO
1270     */
1271    if (cfq_cfqq_idle_window(cfqq) && cfqd->rq_in_driver[BLK_RW_ASYNC])
1272        return false;
1273
1274    /*
1275     * If this is an async queue and we have sync IO in flight, let it wait
1276     */
1277    if (cfqd->sync_flight && !cfq_cfqq_sync(cfqq))
1278        return false;
1279
1280    max_dispatch = cfqd->cfq_quantum;
1281    if (cfq_class_idle(cfqq))
1282        max_dispatch = 1;
1283
1284    /*
1285     * Does this cfqq already have too much IO in flight?
1286     */
1287    if (cfqq->dispatched >= max_dispatch) {
1288        /*
1289         * idle queue must always only have a single IO in flight
1290         */
1291        if (cfq_class_idle(cfqq))
1292            return false;
1293
1294        /*
1295         * We have other queues, don't allow more IO from this one
1296         */
1297        if (cfqd->busy_queues > 1)
1298            return false;
1299
1300        /*
1301         * Sole queue user, allow bigger slice
1302         */
1303        max_dispatch *= 4;
1304    }
1305
1306    /*
1307     * Async queues must wait a bit before being allowed dispatch.
1308     * We also ramp up the dispatch depth gradually for async IO,
1309     * based on the last sync IO we serviced
1310     */
1311    if (!cfq_cfqq_sync(cfqq) && cfqd->cfq_latency) {
1312        unsigned long last_sync = jiffies - cfqd->last_end_sync_rq;
1313        unsigned int depth;
1314
1315        depth = last_sync / cfqd->cfq_slice[1];
1316        if (!depth && !cfqq->dispatched)
1317            depth = 1;
1318        if (depth < max_dispatch)
1319            max_dispatch = depth;
1320    }
1321
1322    /*
1323     * If we're below the current max, allow a dispatch
1324     */
1325    return cfqq->dispatched < max_dispatch;
1326}
1327
1328/*
1329 * Dispatch a request from cfqq, moving them to the request queue
1330 * dispatch list.
1331 */
1332static bool cfq_dispatch_request(struct cfq_data *cfqd, struct cfq_queue *cfqq)
1333{
1334    struct request *rq;
1335
1336    BUG_ON(RB_EMPTY_ROOT(&cfqq->sort_list));
1337
1338    if (!cfq_may_dispatch(cfqd, cfqq))
1339        return false;
1340
1341    /*
1342     * follow expired path, else get first next available
1343     */
1344    rq = cfq_check_fifo(cfqq);
1345    if (!rq)
1346        rq = cfqq->next_rq;
1347
1348    /*
1349     * insert request into driver dispatch list
1350     */
1351    cfq_dispatch_insert(cfqd->queue, rq);
1352
1353    if (!cfqd->active_cic) {
1354        struct cfq_io_context *cic = RQ_CIC(rq);
1355
1356        atomic_long_inc(&cic->ioc->refcount);
1357        cfqd->active_cic = cic;
1358    }
1359
1360    return true;
1361}
1362
1363/*
1364 * Find the cfqq that we need to service and move a request from that to the
1365 * dispatch list
1366 */
1367static int cfq_dispatch_requests(struct request_queue *q, int force)
1368{
1369    struct cfq_data *cfqd = q->elevator->elevator_data;
1370    struct cfq_queue *cfqq;
1371
1372    if (!cfqd->busy_queues)
1373        return 0;
1374
1375    if (unlikely(force))
1376        return cfq_forced_dispatch(cfqd);
1377
1378    cfqq = cfq_select_queue(cfqd);
1379    if (!cfqq)
1380        return 0;
1381
1382    /*
1383     * Dispatch a request from this cfqq, if it is allowed
1384     */
1385    if (!cfq_dispatch_request(cfqd, cfqq))
1386        return 0;
1387
1388    cfqq->slice_dispatch++;
1389    cfq_clear_cfqq_must_dispatch(cfqq);
1390
1391    /*
1392     * expire an async queue immediately if it has used up its slice. idle
1393     * queue always expire after 1 dispatch round.
1394     */
1395    if (cfqd->busy_queues > 1 && ((!cfq_cfqq_sync(cfqq) &&
1396        cfqq->slice_dispatch >= cfq_prio_to_maxrq(cfqd, cfqq)) ||
1397        cfq_class_idle(cfqq))) {
1398        cfqq->slice_end = jiffies + 1;
1399        cfq_slice_expired(cfqd, 0);
1400    }
1401
1402    cfq_log_cfqq(cfqd, cfqq, "dispatched a request");
1403    return 1;
1404}
1405
1406/*
1407 * task holds one reference to the queue, dropped when task exits. each rq
1408 * in-flight on this queue also holds a reference, dropped when rq is freed.
1409 *
1410 * queue lock must be held here.
1411 */
1412static void cfq_put_queue(struct cfq_queue *cfqq)
1413{
1414    struct cfq_data *cfqd = cfqq->cfqd;
1415
1416    BUG_ON(atomic_read(&cfqq->ref) <= 0);
1417
1418    if (!atomic_dec_and_test(&cfqq->ref))
1419        return;
1420
1421    cfq_log_cfqq(cfqd, cfqq, "put_queue");
1422    BUG_ON(rb_first(&cfqq->sort_list));
1423    BUG_ON(cfqq->allocated[READ] + cfqq->allocated[WRITE]);
1424    BUG_ON(cfq_cfqq_on_rr(cfqq));
1425
1426    if (unlikely(cfqd->active_queue == cfqq)) {
1427        __cfq_slice_expired(cfqd, cfqq, 0);
1428        cfq_schedule_dispatch(cfqd);
1429    }
1430
1431    kmem_cache_free(cfq_pool, cfqq);
1432}
1433
1434/*
1435 * Must always be called with the rcu_read_lock() held
1436 */
1437static void
1438__call_for_each_cic(struct io_context *ioc,
1439            void (*func)(struct io_context *, struct cfq_io_context *))
1440{
1441    struct cfq_io_context *cic;
1442    struct hlist_node *n;
1443
1444    hlist_for_each_entry_rcu(cic, n, &ioc->cic_list, cic_list)
1445        func(ioc, cic);
1446}
1447
1448/*
1449 * Call func for each cic attached to this ioc.
1450 */
1451static void
1452call_for_each_cic(struct io_context *ioc,
1453          void (*func)(struct io_context *, struct cfq_io_context *))
1454{
1455    rcu_read_lock();
1456    __call_for_each_cic(ioc, func);
1457    rcu_read_unlock();
1458}
1459
1460static void cfq_cic_free_rcu(struct rcu_head *head)
1461{
1462    struct cfq_io_context *cic;
1463
1464    cic = container_of(head, struct cfq_io_context, rcu_head);
1465
1466    kmem_cache_free(cfq_ioc_pool, cic);
1467    elv_ioc_count_dec(cfq_ioc_count);
1468
1469    if (ioc_gone) {
1470        /*
1471         * CFQ scheduler is exiting, grab exit lock and check
1472         * the pending io context count. If it hits zero,
1473         * complete ioc_gone and set it back to NULL
1474         */
1475        spin_lock(&ioc_gone_lock);
1476        if (ioc_gone && !elv_ioc_count_read(cfq_ioc_count)) {
1477            complete(ioc_gone);
1478            ioc_gone = NULL;
1479        }
1480        spin_unlock(&ioc_gone_lock);
1481    }
1482}
1483
1484static void cfq_cic_free(struct cfq_io_context *cic)
1485{
1486    call_rcu(&cic->rcu_head, cfq_cic_free_rcu);
1487}
1488
1489static void cic_free_func(struct io_context *ioc, struct cfq_io_context *cic)
1490{
1491    unsigned long flags;
1492
1493    BUG_ON(!cic->dead_key);
1494
1495    spin_lock_irqsave(&ioc->lock, flags);
1496    radix_tree_delete(&ioc->radix_root, cic->dead_key);
1497    hlist_del_rcu(&cic->cic_list);
1498    spin_unlock_irqrestore(&ioc->lock, flags);
1499
1500    cfq_cic_free(cic);
1501}
1502
1503/*
1504 * Must be called with rcu_read_lock() held or preemption otherwise disabled.
1505 * Only two callers of this - ->dtor() which is called with the rcu_read_lock(),
1506 * and ->trim() which is called with the task lock held
1507 */
1508static void cfq_free_io_context(struct io_context *ioc)
1509{
1510    /*
1511     * ioc->refcount is zero here, or we are called from elv_unregister(),
1512     * so no more cic's are allowed to be linked into this ioc. So it
1513     * should be ok to iterate over the known list, we will see all cic's
1514     * since no new ones are added.
1515     */
1516    __call_for_each_cic(ioc, cic_free_func);
1517}
1518
1519static void cfq_exit_cfqq(struct cfq_data *cfqd, struct cfq_queue *cfqq)
1520{
1521    if (unlikely(cfqq == cfqd->active_queue)) {
1522        __cfq_slice_expired(cfqd, cfqq, 0);
1523        cfq_schedule_dispatch(cfqd);
1524    }
1525
1526    cfq_put_queue(cfqq);
1527}
1528
1529static void __cfq_exit_single_io_context(struct cfq_data *cfqd,
1530                     struct cfq_io_context *cic)
1531{
1532    struct io_context *ioc = cic->ioc;
1533
1534    list_del_init(&cic->queue_list);
1535
1536    /*
1537     * Make sure key == NULL is seen for dead queues
1538     */
1539    smp_wmb();
1540    cic->dead_key = (unsigned long) cic->key;
1541    cic->key = NULL;
1542
1543    if (ioc->ioc_data == cic)
1544        rcu_assign_pointer(ioc->ioc_data, NULL);
1545
1546    if (cic->cfqq[BLK_RW_ASYNC]) {
1547        cfq_exit_cfqq(cfqd, cic->cfqq[BLK_RW_ASYNC]);
1548        cic->cfqq[BLK_RW_ASYNC] = NULL;
1549    }
1550
1551    if (cic->cfqq[BLK_RW_SYNC]) {
1552        cfq_exit_cfqq(cfqd, cic->cfqq[BLK_RW_SYNC]);
1553        cic->cfqq[BLK_RW_SYNC] = NULL;
1554    }
1555}
1556
1557static void cfq_exit_single_io_context(struct io_context *ioc,
1558                       struct cfq_io_context *cic)
1559{
1560    struct cfq_data *cfqd = cic->key;
1561
1562    if (cfqd) {
1563        struct request_queue *q = cfqd->queue;
1564        unsigned long flags;
1565
1566        spin_lock_irqsave(q->queue_lock, flags);
1567
1568        /*
1569         * Ensure we get a fresh copy of the ->key to prevent
1570         * race between exiting task and queue
1571         */
1572        smp_read_barrier_depends();
1573        if (cic->key)
1574            __cfq_exit_single_io_context(cfqd, cic);
1575
1576        spin_unlock_irqrestore(q->queue_lock, flags);
1577    }
1578}
1579
1580/*
1581 * The process that ioc belongs to has exited, we need to clean up
1582 * and put the internal structures we have that belongs to that process.
1583 */
1584static void cfq_exit_io_context(struct io_context *ioc)
1585{
1586    call_for_each_cic(ioc, cfq_exit_single_io_context);
1587}
1588
1589static struct cfq_io_context *
1590cfq_alloc_io_context(struct cfq_data *cfqd, gfp_t gfp_mask)
1591{
1592    struct cfq_io_context *cic;
1593
1594    cic = kmem_cache_alloc_node(cfq_ioc_pool, gfp_mask | __GFP_ZERO,
1595                            cfqd->queue->node);
1596    if (cic) {
1597        cic->last_end_request = jiffies;
1598        INIT_LIST_HEAD(&cic->queue_list);
1599        INIT_HLIST_NODE(&cic->cic_list);
1600        cic->dtor = cfq_free_io_context;
1601        cic->exit = cfq_exit_io_context;
1602        elv_ioc_count_inc(cfq_ioc_count);
1603    }
1604
1605    return cic;
1606}
1607
1608static void cfq_init_prio_data(struct cfq_queue *cfqq, struct io_context *ioc)
1609{
1610    struct task_struct *tsk = current;
1611    int ioprio_class;
1612
1613    if (!cfq_cfqq_prio_changed(cfqq))
1614        return;
1615
1616    ioprio_class = IOPRIO_PRIO_CLASS(ioc->ioprio);
1617    switch (ioprio_class) {
1618    default:
1619        printk(KERN_ERR "cfq: bad prio %x\n", ioprio_class);
1620    case IOPRIO_CLASS_NONE:
1621        /*
1622         * no prio set, inherit CPU scheduling settings
1623         */
1624        cfqq->ioprio = task_nice_ioprio(tsk);
1625        cfqq->ioprio_class = task_nice_ioclass(tsk);
1626        break;
1627    case IOPRIO_CLASS_RT:
1628        cfqq->ioprio = task_ioprio(ioc);
1629        cfqq->ioprio_class = IOPRIO_CLASS_RT;
1630        break;
1631    case IOPRIO_CLASS_BE:
1632        cfqq->ioprio = task_ioprio(ioc);
1633        cfqq->ioprio_class = IOPRIO_CLASS_BE;
1634        break;
1635    case IOPRIO_CLASS_IDLE:
1636        cfqq->ioprio_class = IOPRIO_CLASS_IDLE;
1637        cfqq->ioprio = 7;
1638        cfq_clear_cfqq_idle_window(cfqq);
1639        break;
1640    }
1641
1642    /*
1643     * keep track of original prio settings in case we have to temporarily
1644     * elevate the priority of this queue
1645     */
1646    cfqq->org_ioprio = cfqq->ioprio;
1647    cfqq->org_ioprio_class = cfqq->ioprio_class;
1648    cfq_clear_cfqq_prio_changed(cfqq);
1649}
1650
1651static void changed_ioprio(struct io_context *ioc, struct cfq_io_context *cic)
1652{
1653    struct cfq_data *cfqd = cic->key;
1654    struct cfq_queue *cfqq;
1655    unsigned long flags;
1656
1657    if (unlikely(!cfqd))
1658        return;
1659
1660    spin_lock_irqsave(cfqd->queue->queue_lock, flags);
1661
1662    cfqq = cic->cfqq[BLK_RW_ASYNC];
1663    if (cfqq) {
1664        struct cfq_queue *new_cfqq;
1665        new_cfqq = cfq_get_queue(cfqd, BLK_RW_ASYNC, cic->ioc,
1666                        GFP_ATOMIC);
1667        if (new_cfqq) {
1668            cic->cfqq[BLK_RW_ASYNC] = new_cfqq;
1669            cfq_put_queue(cfqq);
1670        }
1671    }
1672
1673    cfqq = cic->cfqq[BLK_RW_SYNC];
1674    if (cfqq)
1675        cfq_mark_cfqq_prio_changed(cfqq);
1676
1677    spin_unlock_irqrestore(cfqd->queue->queue_lock, flags);
1678}
1679
1680static void cfq_ioc_set_ioprio(struct io_context *ioc)
1681{
1682    call_for_each_cic(ioc, changed_ioprio);
1683    ioc->ioprio_changed = 0;
1684}
1685
1686static void cfq_init_cfqq(struct cfq_data *cfqd, struct cfq_queue *cfqq,
1687              pid_t pid, bool is_sync)
1688{
1689    RB_CLEAR_NODE(&cfqq->rb_node);
1690    RB_CLEAR_NODE(&cfqq->p_node);
1691    INIT_LIST_HEAD(&cfqq->fifo);
1692
1693    atomic_set(&cfqq->ref, 0);
1694    cfqq->cfqd = cfqd;
1695
1696    cfq_mark_cfqq_prio_changed(cfqq);
1697
1698    if (is_sync) {
1699        if (!cfq_class_idle(cfqq))
1700            cfq_mark_cfqq_idle_window(cfqq);
1701        cfq_mark_cfqq_sync(cfqq);
1702    }
1703    cfqq->pid = pid;
1704}
1705
1706static struct cfq_queue *
1707cfq_find_alloc_queue(struct cfq_data *cfqd, bool is_sync,
1708             struct io_context *ioc, gfp_t gfp_mask)
1709{
1710    struct cfq_queue *cfqq, *new_cfqq = NULL;
1711    struct cfq_io_context *cic;
1712
1713retry:
1714    cic = cfq_cic_lookup(cfqd, ioc);
1715    /* cic always exists here */
1716    cfqq = cic_to_cfqq(cic, is_sync);
1717
1718    /*
1719     * Always try a new alloc if we fell back to the OOM cfqq
1720     * originally, since it should just be a temporary situation.
1721     */
1722    if (!cfqq || cfqq == &cfqd->oom_cfqq) {
1723        cfqq = NULL;
1724        if (new_cfqq) {
1725            cfqq = new_cfqq;
1726            new_cfqq = NULL;
1727        } else if (gfp_mask & __GFP_WAIT) {
1728            spin_unlock_irq(cfqd->queue->queue_lock);
1729            new_cfqq = kmem_cache_alloc_node(cfq_pool,
1730                    gfp_mask | __GFP_ZERO,
1731                    cfqd->queue->node);
1732            spin_lock_irq(cfqd->queue->queue_lock);
1733            if (new_cfqq)
1734                goto retry;
1735        } else {
1736            cfqq = kmem_cache_alloc_node(cfq_pool,
1737                    gfp_mask | __GFP_ZERO,
1738                    cfqd->queue->node);
1739        }
1740
1741        if (cfqq) {
1742            cfq_init_cfqq(cfqd, cfqq, current->pid, is_sync);
1743            cfq_init_prio_data(cfqq, ioc);
1744            cfq_log_cfqq(cfqd, cfqq, "alloced");
1745        } else
1746            cfqq = &cfqd->oom_cfqq;
1747    }
1748
1749    if (new_cfqq)
1750        kmem_cache_free(cfq_pool, new_cfqq);
1751
1752    return cfqq;
1753}
1754
1755static struct cfq_queue **
1756cfq_async_queue_prio(struct cfq_data *cfqd, int ioprio_class, int ioprio)
1757{
1758    switch (ioprio_class) {
1759    case IOPRIO_CLASS_RT:
1760        return &cfqd->async_cfqq[0][ioprio];
1761    case IOPRIO_CLASS_BE:
1762        return &cfqd->async_cfqq[1][ioprio];
1763    case IOPRIO_CLASS_IDLE:
1764        return &cfqd->async_idle_cfqq;
1765    default:
1766        BUG();
1767    }
1768}
1769
1770static struct cfq_queue *
1771cfq_get_queue(struct cfq_data *cfqd, bool is_sync, struct io_context *ioc,
1772          gfp_t gfp_mask)
1773{
1774    const int ioprio = task_ioprio(ioc);
1775    const int ioprio_class = task_ioprio_class(ioc);
1776    struct cfq_queue **async_cfqq = NULL;
1777    struct cfq_queue *cfqq = NULL;
1778
1779    if (!is_sync) {
1780        async_cfqq = cfq_async_queue_prio(cfqd, ioprio_class, ioprio);
1781        cfqq = *async_cfqq;
1782    }
1783
1784    if (!cfqq)
1785        cfqq = cfq_find_alloc_queue(cfqd, is_sync, ioc, gfp_mask);
1786
1787    /*
1788     * pin the queue now that it's allocated, scheduler exit will prune it
1789     */
1790    if (!is_sync && !(*async_cfqq)) {
1791        atomic_inc(&cfqq->ref);
1792        *async_cfqq = cfqq;
1793    }
1794
1795    atomic_inc(&cfqq->ref);
1796    return cfqq;
1797}
1798
1799/*
1800 * We drop cfq io contexts lazily, so we may find a dead one.
1801 */
1802static void
1803cfq_drop_dead_cic(struct cfq_data *cfqd, struct io_context *ioc,
1804          struct cfq_io_context *cic)
1805{
1806    unsigned long flags;
1807
1808    WARN_ON(!list_empty(&cic->queue_list));
1809
1810    spin_lock_irqsave(&ioc->lock, flags);
1811
1812    BUG_ON(ioc->ioc_data == cic);
1813
1814    radix_tree_delete(&ioc->radix_root, (unsigned long) cfqd);
1815    hlist_del_rcu(&cic->cic_list);
1816    spin_unlock_irqrestore(&ioc->lock, flags);
1817
1818    cfq_cic_free(cic);
1819}
1820
1821static struct cfq_io_context *
1822cfq_cic_lookup(struct cfq_data *cfqd, struct io_context *ioc)
1823{
1824    struct cfq_io_context *cic;
1825    unsigned long flags;
1826    void *k;
1827
1828    if (unlikely(!ioc))
1829        return NULL;
1830
1831    rcu_read_lock();
1832
1833    /*
1834     * we maintain a last-hit cache, to avoid browsing over the tree
1835     */
1836    cic = rcu_dereference(ioc->ioc_data);
1837    if (cic && cic->key == cfqd) {
1838        rcu_read_unlock();
1839        return cic;
1840    }
1841
1842    do {
1843        cic = radix_tree_lookup(&ioc->radix_root, (unsigned long) cfqd);
1844        rcu_read_unlock();
1845        if (!cic)
1846            break;
1847        /* ->key must be copied to avoid race with cfq_exit_queue() */
1848        k = cic->key;
1849        if (unlikely(!k)) {
1850            cfq_drop_dead_cic(cfqd, ioc, cic);
1851            rcu_read_lock();
1852            continue;
1853        }
1854
1855        spin_lock_irqsave(&ioc->lock, flags);
1856        rcu_assign_pointer(ioc->ioc_data, cic);
1857        spin_unlock_irqrestore(&ioc->lock, flags);
1858        break;
1859    } while (1);
1860
1861    return cic;
1862}
1863
1864/*
1865 * Add cic into ioc, using cfqd as the search key. This enables us to lookup
1866 * the process specific cfq io context when entered from the block layer.
1867 * Also adds the cic to a per-cfqd list, used when this queue is removed.
1868 */
1869static int cfq_cic_link(struct cfq_data *cfqd, struct io_context *ioc,
1870            struct cfq_io_context *cic, gfp_t gfp_mask)
1871{
1872    unsigned long flags;
1873    int ret;
1874
1875    ret = radix_tree_preload(gfp_mask);
1876    if (!ret) {
1877        cic->ioc = ioc;
1878        cic->key = cfqd;
1879
1880        spin_lock_irqsave(&ioc->lock, flags);
1881        ret = radix_tree_insert(&ioc->radix_root,
1882                        (unsigned long) cfqd, cic);
1883        if (!ret)
1884            hlist_add_head_rcu(&cic->cic_list, &ioc->cic_list);
1885        spin_unlock_irqrestore(&ioc->lock, flags);
1886
1887        radix_tree_preload_end();
1888
1889        if (!ret) {
1890            spin_lock_irqsave(cfqd->queue->queue_lock, flags);
1891            list_add(&cic->queue_list, &cfqd->cic_list);
1892            spin_unlock_irqrestore(cfqd->queue->queue_lock, flags);
1893        }
1894    }
1895
1896    if (ret)
1897        printk(KERN_ERR "cfq: cic link failed!\n");
1898
1899    return ret;
1900}
1901
1902/*
1903 * Setup general io context and cfq io context. There can be several cfq
1904 * io contexts per general io context, if this process is doing io to more
1905 * than one device managed by cfq.
1906 */
1907static struct cfq_io_context *
1908cfq_get_io_context(struct cfq_data *cfqd, gfp_t gfp_mask)
1909{
1910    struct io_context *ioc = NULL;
1911    struct cfq_io_context *cic;
1912
1913    might_sleep_if(gfp_mask & __GFP_WAIT);
1914
1915    ioc = get_io_context(gfp_mask, cfqd->queue->node);
1916    if (!ioc)
1917        return NULL;
1918
1919    cic = cfq_cic_lookup(cfqd, ioc);
1920    if (cic)
1921        goto out;
1922
1923    cic = cfq_alloc_io_context(cfqd, gfp_mask);
1924    if (cic == NULL)
1925        goto err;
1926
1927    if (cfq_cic_link(cfqd, ioc, cic, gfp_mask))
1928        goto err_free;
1929
1930out:
1931    smp_read_barrier_depends();
1932    if (unlikely(ioc->ioprio_changed))
1933        cfq_ioc_set_ioprio(ioc);
1934
1935    return cic;
1936err_free:
1937    cfq_cic_free(cic);
1938err:
1939    put_io_context(ioc);
1940    return NULL;
1941}
1942
1943static void
1944cfq_update_io_thinktime(struct cfq_data *cfqd, struct cfq_io_context *cic)
1945{
1946    unsigned long elapsed = jiffies - cic->last_end_request;
1947    unsigned long ttime = min(elapsed, 2UL * cfqd->cfq_slice_idle);
1948
1949    cic->ttime_samples = (7*cic->ttime_samples + 256) / 8;
1950    cic->ttime_total = (7*cic->ttime_total + 256*ttime) / 8;
1951    cic->ttime_mean = (cic->ttime_total + 128) / cic->ttime_samples;
1952}
1953
1954static void
1955cfq_update_io_seektime(struct cfq_data *cfqd, struct cfq_io_context *cic,
1956               struct request *rq)
1957{
1958    sector_t sdist;
1959    u64 total;
1960
1961    if (!cic->last_request_pos)
1962        sdist = 0;
1963    else if (cic->last_request_pos < blk_rq_pos(rq))
1964        sdist = blk_rq_pos(rq) - cic->last_request_pos;
1965    else
1966        sdist = cic->last_request_pos - blk_rq_pos(rq);
1967
1968    /*
1969     * Don't allow the seek distance to get too large from the
1970     * odd fragment, pagein, etc
1971     */
1972    if (cic->seek_samples <= 60) /* second&third seek */
1973        sdist = min(sdist, (cic->seek_mean * 4) + 2*1024*1024);
1974    else
1975        sdist = min(sdist, (cic->seek_mean * 4) + 2*1024*64);
1976
1977    cic->seek_samples = (7*cic->seek_samples + 256) / 8;
1978    cic->seek_total = (7*cic->seek_total + (u64)256*sdist) / 8;
1979    total = cic->seek_total + (cic->seek_samples/2);
1980    do_div(total, cic->seek_samples);
1981    cic->seek_mean = (sector_t)total;
1982}
1983
1984/*
1985 * Disable idle window if the process thinks too long or seeks so much that
1986 * it doesn't matter
1987 */
1988static void
1989cfq_update_idle_window(struct cfq_data *cfqd, struct cfq_queue *cfqq,
1990               struct cfq_io_context *cic)
1991{
1992    int old_idle, enable_idle;
1993
1994    /*
1995     * Don't idle for async or idle io prio class
1996     */
1997    if (!cfq_cfqq_sync(cfqq) || cfq_class_idle(cfqq))
1998        return;
1999
2000    enable_idle = old_idle = cfq_cfqq_idle_window(cfqq);
2001
2002    if (!atomic_read(&cic->ioc->nr_tasks) || !cfqd->cfq_slice_idle ||
2003        (!cfqd->cfq_latency && cfqd->hw_tag && CIC_SEEKY(cic)))
2004        enable_idle = 0;
2005    else if (sample_valid(cic->ttime_samples)) {
2006        unsigned int slice_idle = cfqd->cfq_slice_idle;
2007        if (sample_valid(cic->seek_samples) && CIC_SEEKY(cic))
2008            slice_idle = msecs_to_jiffies(CFQ_MIN_TT);
2009        if (cic->ttime_mean > slice_idle)
2010            enable_idle = 0;
2011        else
2012            enable_idle = 1;
2013    }
2014
2015    if (old_idle != enable_idle) {
2016        cfq_log_cfqq(cfqd, cfqq, "idle=%d", enable_idle);
2017        if (enable_idle)
2018            cfq_mark_cfqq_idle_window(cfqq);
2019        else
2020            cfq_clear_cfqq_idle_window(cfqq);
2021    }
2022}
2023
2024/*
2025 * Check if new_cfqq should preempt the currently active queue. Return 0 for
2026 * no or if we aren't sure, a 1 will cause a preempt.
2027 */
2028static bool
2029cfq_should_preempt(struct cfq_data *cfqd, struct cfq_queue *new_cfqq,
2030           struct request *rq)
2031{
2032    struct cfq_queue *cfqq;
2033
2034    cfqq = cfqd->active_queue;
2035    if (!cfqq)
2036        return false;
2037
2038    if (cfq_slice_used(cfqq))
2039        return true;
2040
2041    if (cfq_class_idle(new_cfqq))
2042        return false;
2043
2044    if (cfq_class_idle(cfqq))
2045        return true;
2046
2047    /*
2048     * if the new request is sync, but the currently running queue is
2049     * not, let the sync request have priority.
2050     */
2051    if (rq_is_sync(rq) && !cfq_cfqq_sync(cfqq))
2052        return true;
2053
2054    /*
2055     * So both queues are sync. Let the new request get disk time if
2056     * it's a metadata request and the current queue is doing regular IO.
2057     */
2058    if (rq_is_meta(rq) && !cfqq->meta_pending)
2059        return true;
2060
2061    /*
2062     * Allow an RT request to pre-empt an ongoing non-RT cfqq timeslice.
2063     */
2064    if (cfq_class_rt(new_cfqq) && !cfq_class_rt(cfqq))
2065        return true;
2066
2067    if (!cfqd->active_cic || !cfq_cfqq_wait_request(cfqq))
2068        return false;
2069
2070    /*
2071     * if this request is as-good as one we would expect from the
2072     * current cfqq, let it preempt
2073     */
2074    if (cfq_rq_close(cfqd, rq) && (!cfq_cfqq_coop(new_cfqq) ||
2075        cfqd->busy_queues == 1)) {
2076        /*
2077         * Mark new queue coop_preempt, so its coop flag will not be
2078         * cleared when new queue gets scheduled at the very first time
2079         */
2080        cfq_mark_cfqq_coop_preempt(new_cfqq);
2081        cfq_mark_cfqq_coop(new_cfqq);
2082        return true;
2083    }
2084
2085    return false;
2086}
2087
2088/*
2089 * cfqq preempts the active queue. if we allowed preempt with no slice left,
2090 * let it have half of its nominal slice.
2091 */
2092static void cfq_preempt_queue(struct cfq_data *cfqd, struct cfq_queue *cfqq)
2093{
2094    cfq_log_cfqq(cfqd, cfqq, "preempt");
2095    cfq_slice_expired(cfqd, 1);
2096
2097    /*
2098     * Put the new queue at the front of the of the current list,
2099     * so we know that it will be selected next.
2100     */
2101    BUG_ON(!cfq_cfqq_on_rr(cfqq));
2102
2103    cfq_service_tree_add(cfqd, cfqq, 1);
2104
2105    cfqq->slice_end = 0;
2106    cfq_mark_cfqq_slice_new(cfqq);
2107}
2108
2109/*
2110 * Called when a new fs request (rq) is added (to cfqq). Check if there's
2111 * something we should do about it
2112 */
2113static void
2114cfq_rq_enqueued(struct cfq_data *cfqd, struct cfq_queue *cfqq,
2115        struct request *rq)
2116{
2117    struct cfq_io_context *cic = RQ_CIC(rq);
2118
2119    cfqd->rq_queued++;
2120    if (rq_is_meta(rq))
2121        cfqq->meta_pending++;
2122
2123    cfq_update_io_thinktime(cfqd, cic);
2124    cfq_update_io_seektime(cfqd, cic, rq);
2125    cfq_update_idle_window(cfqd, cfqq, cic);
2126
2127    cic->last_request_pos = blk_rq_pos(rq) + blk_rq_sectors(rq);
2128
2129    if (cfqq == cfqd->active_queue) {
2130        /*
2131         * Remember that we saw a request from this process, but
2132         * don't start queuing just yet. Otherwise we risk seeing lots
2133         * of tiny requests, because we disrupt the normal plugging
2134         * and merging. If the request is already larger than a single
2135         * page, let it rip immediately. For that case we assume that
2136         * merging is already done. Ditto for a busy system that
2137         * has other work pending, don't risk delaying until the
2138         * idle timer unplug to continue working.
2139         */
2140        if (cfq_cfqq_wait_request(cfqq)) {
2141            if (blk_rq_bytes(rq) > PAGE_CACHE_SIZE ||
2142                cfqd->busy_queues > 1) {
2143                del_timer(&cfqd->idle_slice_timer);
2144            __blk_run_queue(cfqd->queue);
2145            }
2146            cfq_mark_cfqq_must_dispatch(cfqq);
2147        }
2148    } else if (cfq_should_preempt(cfqd, cfqq, rq)) {
2149        /*
2150         * not the active queue - expire current slice if it is
2151         * idle and has expired it's mean thinktime or this new queue
2152         * has some old slice time left and is of higher priority or
2153         * this new queue is RT and the current one is BE
2154         */
2155        cfq_preempt_queue(cfqd, cfqq);
2156        __blk_run_queue(cfqd->queue);
2157    }
2158}
2159
2160static void cfq_insert_request(struct request_queue *q, struct request *rq)
2161{
2162    struct cfq_data *cfqd = q->elevator->elevator_data;
2163    struct cfq_queue *cfqq = RQ_CFQQ(rq);
2164
2165    cfq_log_cfqq(cfqd, cfqq, "insert_request");
2166    cfq_init_prio_data(cfqq, RQ_CIC(rq)->ioc);
2167
2168    cfq_add_rq_rb(rq);
2169
2170    rq_set_fifo_time(rq, jiffies + cfqd->cfq_fifo_expire[rq_is_sync(rq)]);
2171    list_add_tail(&rq->queuelist, &cfqq->fifo);
2172
2173    cfq_rq_enqueued(cfqd, cfqq, rq);
2174}
2175
2176/*
2177 * Update hw_tag based on peak queue depth over 50 samples under
2178 * sufficient load.
2179 */
2180static void cfq_update_hw_tag(struct cfq_data *cfqd)
2181{
2182    if (rq_in_driver(cfqd) > cfqd->rq_in_driver_peak)
2183        cfqd->rq_in_driver_peak = rq_in_driver(cfqd);
2184
2185    if (cfqd->rq_queued <= CFQ_HW_QUEUE_MIN &&
2186        rq_in_driver(cfqd) <= CFQ_HW_QUEUE_MIN)
2187        return;
2188
2189    if (cfqd->hw_tag_samples++ < 50)
2190        return;
2191
2192    if (cfqd->rq_in_driver_peak >= CFQ_HW_QUEUE_MIN)
2193        cfqd->hw_tag = 1;
2194    else
2195        cfqd->hw_tag = 0;
2196
2197    cfqd->hw_tag_samples = 0;
2198    cfqd->rq_in_driver_peak = 0;
2199}
2200
2201static void cfq_completed_request(struct request_queue *q, struct request *rq)
2202{
2203    struct cfq_queue *cfqq = RQ_CFQQ(rq);
2204    struct cfq_data *cfqd = cfqq->cfqd;
2205    const int sync = rq_is_sync(rq);
2206    unsigned long now;
2207
2208    now = jiffies;
2209    cfq_log_cfqq(cfqd, cfqq, "complete");
2210
2211    cfq_update_hw_tag(cfqd);
2212
2213    WARN_ON(!cfqd->rq_in_driver[sync]);
2214    WARN_ON(!cfqq->dispatched);
2215    cfqd->rq_in_driver[sync]--;
2216    cfqq->dispatched--;
2217
2218    if (cfq_cfqq_sync(cfqq))
2219        cfqd->sync_flight--;
2220
2221    if (sync) {
2222        RQ_CIC(rq)->last_end_request = now;
2223        cfqd->last_end_sync_rq = now;
2224    }
2225
2226    /*
2227     * If this is the active queue, check if it needs to be expired,
2228     * or if we want to idle in case it has no pending requests.
2229     */
2230    if (cfqd->active_queue == cfqq) {
2231        const bool cfqq_empty = RB_EMPTY_ROOT(&cfqq->sort_list);
2232
2233        if (cfq_cfqq_slice_new(cfqq)) {
2234            cfq_set_prio_slice(cfqd, cfqq);
2235            cfq_clear_cfqq_slice_new(cfqq);
2236        }
2237        /*
2238         * If there are no requests waiting in this queue, and
2239         * there are other queues ready to issue requests, AND
2240         * those other queues are issuing requests within our
2241         * mean seek distance, give them a chance to run instead
2242         * of idling.
2243         */
2244        if (cfq_slice_used(cfqq) || cfq_class_idle(cfqq))
2245            cfq_slice_expired(cfqd, 1);
2246        else if (cfqq_empty && !cfq_close_cooperator(cfqd, cfqq, 1) &&
2247             sync && !rq_noidle(rq))
2248            cfq_arm_slice_timer(cfqd);
2249    }
2250
2251    if (!rq_in_driver(cfqd))
2252        cfq_schedule_dispatch(cfqd);
2253}
2254
2255/*
2256 * we temporarily boost lower priority queues if they are holding fs exclusive
2257 * resources. they are boosted to normal prio (CLASS_BE/4)
2258 */
2259static void cfq_prio_boost(struct cfq_queue *cfqq)
2260{
2261    if (has_fs_excl()) {
2262        /*
2263         * boost idle prio on transactions that would lock out other
2264         * users of the filesystem
2265         */
2266        if (cfq_class_idle(cfqq))
2267            cfqq->ioprio_class = IOPRIO_CLASS_BE;
2268        if (cfqq->ioprio > IOPRIO_NORM)
2269            cfqq->ioprio = IOPRIO_NORM;
2270    } else {
2271        /*
2272         * check if we need to unboost the queue
2273         */
2274        if (cfqq->ioprio_class != cfqq->org_ioprio_class)
2275            cfqq->ioprio_class = cfqq->org_ioprio_class;
2276        if (cfqq->ioprio != cfqq->org_ioprio)
2277            cfqq->ioprio = cfqq->org_ioprio;
2278    }
2279}
2280
2281static inline int __cfq_may_queue(struct cfq_queue *cfqq)
2282{
2283    if (cfq_cfqq_wait_request(cfqq) && !cfq_cfqq_must_alloc_slice(cfqq)) {
2284        cfq_mark_cfqq_must_alloc_slice(cfqq);
2285        return ELV_MQUEUE_MUST;
2286    }
2287
2288    return ELV_MQUEUE_MAY;
2289}
2290
2291static int cfq_may_queue(struct request_queue *q, int rw)
2292{
2293    struct cfq_data *cfqd = q->elevator->elevator_data;
2294    struct task_struct *tsk = current;
2295    struct cfq_io_context *cic;
2296    struct cfq_queue *cfqq;
2297
2298    /*
2299     * don't force setup of a queue from here, as a call to may_queue
2300     * does not necessarily imply that a request actually will be queued.
2301     * so just lookup a possibly existing queue, or return 'may queue'
2302     * if that fails
2303     */
2304    cic = cfq_cic_lookup(cfqd, tsk->io_context);
2305    if (!cic)
2306        return ELV_MQUEUE_MAY;
2307
2308    cfqq = cic_to_cfqq(cic, rw_is_sync(rw));
2309    if (cfqq) {
2310        cfq_init_prio_data(cfqq, cic->ioc);
2311        cfq_prio_boost(cfqq);
2312
2313        return __cfq_may_queue(cfqq);
2314    }
2315
2316    return ELV_MQUEUE_MAY;
2317}
2318
2319/*
2320 * queue lock held here
2321 */
2322static void cfq_put_request(struct request *rq)
2323{
2324    struct cfq_queue *cfqq = RQ_CFQQ(rq);
2325
2326    if (cfqq) {
2327        const int rw = rq_data_dir(rq);
2328
2329        BUG_ON(!cfqq->allocated[rw]);
2330        cfqq->allocated[rw]--;
2331
2332        put_io_context(RQ_CIC(rq)->ioc);
2333
2334        rq->elevator_private = NULL;
2335        rq->elevator_private2 = NULL;
2336
2337        cfq_put_queue(cfqq);
2338    }
2339}
2340
2341/*
2342 * Allocate cfq data structures associated with this request.
2343 */
2344static int
2345cfq_set_request(struct request_queue *q, struct request *rq, gfp_t gfp_mask)
2346{
2347    struct cfq_data *cfqd = q->elevator->elevator_data;
2348    struct cfq_io_context *cic;
2349    const int rw = rq_data_dir(rq);
2350    const bool is_sync = rq_is_sync(rq);
2351    struct cfq_queue *cfqq;
2352    unsigned long flags;
2353
2354    might_sleep_if(gfp_mask & __GFP_WAIT);
2355
2356    cic = cfq_get_io_context(cfqd, gfp_mask);
2357
2358    spin_lock_irqsave(q->queue_lock, flags);
2359
2360    if (!cic)
2361        goto queue_fail;
2362
2363    cfqq = cic_to_cfqq(cic, is_sync);
2364    if (!cfqq || cfqq == &cfqd->oom_cfqq) {
2365        cfqq = cfq_get_queue(cfqd, is_sync, cic->ioc, gfp_mask);
2366        cic_set_cfqq(cic, cfqq, is_sync);
2367    }
2368
2369    cfqq->allocated[rw]++;
2370    atomic_inc(&cfqq->ref);
2371
2372    spin_unlock_irqrestore(q->queue_lock, flags);
2373
2374    rq->elevator_private = cic;
2375    rq->elevator_private2 = cfqq;
2376    return 0;
2377
2378queue_fail:
2379    if (cic)
2380        put_io_context(cic->ioc);
2381
2382    cfq_schedule_dispatch(cfqd);
2383    spin_unlock_irqrestore(q->queue_lock, flags);
2384    cfq_log(cfqd, "set_request fail");
2385    return 1;
2386}
2387
2388static void cfq_kick_queue(struct work_struct *work)
2389{
2390    struct cfq_data *cfqd =
2391        container_of(work, struct cfq_data, unplug_work);
2392    struct request_queue *q = cfqd->queue;
2393
2394    spin_lock_irq(q->queue_lock);
2395    __blk_run_queue(cfqd->queue);
2396    spin_unlock_irq(q->queue_lock);
2397}
2398
2399/*
2400 * Timer running if the active_queue is currently idling inside its time slice
2401 */
2402static void cfq_idle_slice_timer(unsigned long data)
2403{
2404    struct cfq_data *cfqd = (struct cfq_data *) data;
2405    struct cfq_queue *cfqq;
2406    unsigned long flags;
2407    int timed_out = 1;
2408
2409    cfq_log(cfqd, "idle timer fired");
2410
2411    spin_lock_irqsave(cfqd->queue->queue_lock, flags);
2412
2413    cfqq = cfqd->active_queue;
2414    if (cfqq) {
2415        timed_out = 0;
2416
2417        /*
2418         * We saw a request before the queue expired, let it through
2419         */
2420        if (cfq_cfqq_must_dispatch(cfqq))
2421            goto out_kick;
2422
2423        /*
2424         * expired
2425         */
2426        if (cfq_slice_used(cfqq))
2427            goto expire;
2428
2429        /*
2430         * only expire and reinvoke request handler, if there are
2431         * other queues with pending requests
2432         */
2433        if (!cfqd->busy_queues)
2434            goto out_cont;
2435
2436        /*
2437         * not expired and it has a request pending, let it dispatch
2438         */
2439        if (!RB_EMPTY_ROOT(&cfqq->sort_list))
2440            goto out_kick;
2441    }
2442expire:
2443    cfq_slice_expired(cfqd, timed_out);
2444out_kick:
2445    cfq_schedule_dispatch(cfqd);
2446out_cont:
2447    spin_unlock_irqrestore(cfqd->queue->queue_lock, flags);
2448}
2449
2450static void cfq_shutdown_timer_wq(struct cfq_data *cfqd)
2451{
2452    del_timer_sync(&cfqd->idle_slice_timer);
2453    cancel_work_sync(&cfqd->unplug_work);
2454}
2455
2456static void cfq_put_async_queues(struct cfq_data *cfqd)
2457{
2458    int i;
2459
2460    for (i = 0; i < IOPRIO_BE_NR; i++) {
2461        if (cfqd->async_cfqq[0][i])
2462            cfq_put_queue(cfqd->async_cfqq[0][i]);
2463        if (cfqd->async_cfqq[1][i])
2464            cfq_put_queue(cfqd->async_cfqq[1][i]);
2465    }
2466
2467    if (cfqd->async_idle_cfqq)
2468        cfq_put_queue(cfqd->async_idle_cfqq);
2469}
2470
2471static void cfq_exit_queue(struct elevator_queue *e)
2472{
2473    struct cfq_data *cfqd = e->elevator_data;
2474    struct request_queue *q = cfqd->queue;
2475
2476    cfq_shutdown_timer_wq(cfqd);
2477
2478    spin_lock_irq(q->queue_lock);
2479
2480    if (cfqd->active_queue)
2481        __cfq_slice_expired(cfqd, cfqd->active_queue, 0);
2482
2483    while (!list_empty(&cfqd->cic_list)) {
2484        struct cfq_io_context *cic = list_entry(cfqd->cic_list.next,
2485                            struct cfq_io_context,
2486                            queue_list);
2487
2488        __cfq_exit_single_io_context(cfqd, cic);
2489    }
2490
2491    cfq_put_async_queues(cfqd);
2492
2493    spin_unlock_irq(q->queue_lock);
2494
2495    cfq_shutdown_timer_wq(cfqd);
2496
2497    kfree(cfqd);
2498}
2499
2500static void *cfq_init_queue(struct request_queue *q)
2501{
2502    struct cfq_data *cfqd;
2503    int i;
2504
2505    cfqd = kmalloc_node(sizeof(*cfqd), GFP_KERNEL | __GFP_ZERO, q->node);
2506    if (!cfqd)
2507        return NULL;
2508
2509    cfqd->service_tree = CFQ_RB_ROOT;
2510
2511    /*
2512     * Not strictly needed (since RB_ROOT just clears the node and we
2513     * zeroed cfqd on alloc), but better be safe in case someone decides
2514     * to add magic to the rb code
2515     */
2516    for (i = 0; i < CFQ_PRIO_LISTS; i++)
2517        cfqd->prio_trees[i] = RB_ROOT;
2518
2519    /*
2520     * Our fallback cfqq if cfq_find_alloc_queue() runs into OOM issues.
2521     * Grab a permanent reference to it, so that the normal code flow
2522     * will not attempt to free it.
2523     */
2524    cfq_init_cfqq(cfqd, &cfqd->oom_cfqq, 1, 0);
2525    atomic_inc(&cfqd->oom_cfqq.ref);
2526
2527    INIT_LIST_HEAD(&cfqd->cic_list);
2528
2529    cfqd->queue = q;
2530
2531    init_timer(&cfqd->idle_slice_timer);
2532    cfqd->idle_slice_timer.function = cfq_idle_slice_timer;
2533    cfqd->idle_slice_timer.data = (unsigned long) cfqd;
2534
2535    INIT_WORK(&cfqd->unplug_work, cfq_kick_queue);
2536
2537    cfqd->cfq_quantum = cfq_quantum;
2538    cfqd->cfq_fifo_expire[0] = cfq_fifo_expire[0];
2539    cfqd->cfq_fifo_expire[1] = cfq_fifo_expire[1];
2540    cfqd->cfq_back_max = cfq_back_max;
2541    cfqd->cfq_back_penalty = cfq_back_penalty;
2542    cfqd->cfq_slice[0] = cfq_slice_async;
2543    cfqd->cfq_slice[1] = cfq_slice_sync;
2544    cfqd->cfq_slice_async_rq = cfq_slice_async_rq;
2545    cfqd->cfq_slice_idle = cfq_slice_idle;
2546    cfqd->cfq_latency = 1;
2547    cfqd->hw_tag = 1;
2548    cfqd->last_end_sync_rq = jiffies;
2549    return cfqd;
2550}
2551
2552static void cfq_slab_kill(void)
2553{
2554    /*
2555     * Caller already ensured that pending RCU callbacks are completed,
2556     * so we should have no busy allocations at this point.
2557     */
2558    if (cfq_pool)
2559        kmem_cache_destroy(cfq_pool);
2560    if (cfq_ioc_pool)
2561        kmem_cache_destroy(cfq_ioc_pool);
2562}
2563
2564static int __init cfq_slab_setup(void)
2565{
2566    cfq_pool = KMEM_CACHE(cfq_queue, 0);
2567    if (!cfq_pool)
2568        goto fail;
2569
2570    cfq_ioc_pool = KMEM_CACHE(cfq_io_context, 0);
2571    if (!cfq_ioc_pool)
2572        goto fail;
2573
2574    return 0;
2575fail:
2576    cfq_slab_kill();
2577    return -ENOMEM;
2578}
2579
2580/*
2581 * sysfs parts below -->
2582 */
2583static ssize_t
2584cfq_var_show(unsigned int var, char *page)
2585{
2586    return sprintf(page, "%d\n", var);
2587}
2588
2589static ssize_t
2590cfq_var_store(unsigned int *var, const char *page, size_t count)
2591{
2592    char *p = (char *) page;
2593
2594    *var = simple_strtoul(p, &p, 10);
2595    return count;
2596}
2597
2598#define SHOW_FUNCTION(__FUNC, __VAR, __CONV) \
2599static ssize_t __FUNC(struct elevator_queue *e, char *page) \
2600{ \
2601    struct cfq_data *cfqd = e->elevator_data; \
2602    unsigned int __data = __VAR; \
2603    if (__CONV) \
2604        __data = jiffies_to_msecs(__data); \
2605    return cfq_var_show(__data, (page)); \
2606}
2607SHOW_FUNCTION(cfq_quantum_show, cfqd->cfq_quantum, 0);
2608SHOW_FUNCTION(cfq_fifo_expire_sync_show, cfqd->cfq_fifo_expire[1], 1);
2609SHOW_FUNCTION(cfq_fifo_expire_async_show, cfqd->cfq_fifo_expire[0], 1);
2610SHOW_FUNCTION(cfq_back_seek_max_show, cfqd->cfq_back_max, 0);
2611SHOW_FUNCTION(cfq_back_seek_penalty_show, cfqd->cfq_back_penalty, 0);
2612SHOW_FUNCTION(cfq_slice_idle_show, cfqd->cfq_slice_idle, 1);
2613SHOW_FUNCTION(cfq_slice_sync_show, cfqd->cfq_slice[1], 1);
2614SHOW_FUNCTION(cfq_slice_async_show, cfqd->cfq_slice[0], 1);
2615SHOW_FUNCTION(cfq_slice_async_rq_show, cfqd->cfq_slice_async_rq, 0);
2616SHOW_FUNCTION(cfq_low_latency_show, cfqd->cfq_latency, 0);
2617#undef SHOW_FUNCTION
2618
2619#define STORE_FUNCTION(__FUNC, __PTR, MIN, MAX, __CONV) \
2620static ssize_t __FUNC(struct elevator_queue *e, const char *page, size_t count) \
2621{ \
2622    struct cfq_data *cfqd = e->elevator_data; \
2623    unsigned int __data; \
2624    int ret = cfq_var_store(&__data, (page), count); \
2625    if (__data < (MIN)) \
2626        __data = (MIN); \
2627    else if (__data > (MAX)) \
2628        __data = (MAX); \
2629    if (__CONV) \
2630        *(__PTR) = msecs_to_jiffies(__data); \
2631    else \
2632        *(__PTR) = __data; \
2633    return ret; \
2634}
2635STORE_FUNCTION(cfq_quantum_store, &cfqd->cfq_quantum, 1, UINT_MAX, 0);
2636STORE_FUNCTION(cfq_fifo_expire_sync_store, &cfqd->cfq_fifo_expire[1], 1,
2637        UINT_MAX, 1);
2638STORE_FUNCTION(cfq_fifo_expire_async_store, &cfqd->cfq_fifo_expire[0], 1,
2639        UINT_MAX, 1);
2640STORE_FUNCTION(cfq_back_seek_max_store, &cfqd->cfq_back_max, 0, UINT_MAX, 0);
2641STORE_FUNCTION(cfq_back_seek_penalty_store, &cfqd->cfq_back_penalty, 1,
2642        UINT_MAX, 0);
2643STORE_FUNCTION(cfq_slice_idle_store, &cfqd->cfq_slice_idle, 0, UINT_MAX, 1);
2644STORE_FUNCTION(cfq_slice_sync_store, &cfqd->cfq_slice[1], 1, UINT_MAX, 1);
2645STORE_FUNCTION(cfq_slice_async_store, &cfqd->cfq_slice[0], 1, UINT_MAX, 1);
2646STORE_FUNCTION(cfq_slice_async_rq_store, &cfqd->cfq_slice_async_rq, 1,
2647        UINT_MAX, 0);
2648STORE_FUNCTION(cfq_low_latency_store, &cfqd->cfq_latency, 0, 1, 0);
2649#undef STORE_FUNCTION
2650
2651#define CFQ_ATTR(name) \
2652    __ATTR(name, S_IRUGO|S_IWUSR, cfq_##name##_show, cfq_##name##_store)
2653
2654static struct elv_fs_entry cfq_attrs[] = {
2655    CFQ_ATTR(quantum),
2656    CFQ_ATTR(fifo_expire_sync),
2657    CFQ_ATTR(fifo_expire_async),
2658    CFQ_ATTR(back_seek_max),
2659    CFQ_ATTR(back_seek_penalty),
2660    CFQ_ATTR(slice_sync),
2661    CFQ_ATTR(slice_async),
2662    CFQ_ATTR(slice_async_rq),
2663    CFQ_ATTR(slice_idle),
2664    CFQ_ATTR(low_latency),
2665    __ATTR_NULL
2666};
2667
2668static struct elevator_type iosched_cfq = {
2669    .ops = {
2670        .elevator_merge_fn = cfq_merge,
2671        .elevator_merged_fn = cfq_merged_request,
2672        .elevator_merge_req_fn = cfq_merged_requests,
2673        .elevator_allow_merge_fn = cfq_allow_merge,
2674        .elevator_dispatch_fn = cfq_dispatch_requests,
2675        .elevator_add_req_fn = cfq_insert_request,
2676        .elevator_activate_req_fn = cfq_activate_request,
2677        .elevator_deactivate_req_fn = cfq_deactivate_request,
2678        .elevator_queue_empty_fn = cfq_queue_empty,
2679        .elevator_completed_req_fn = cfq_completed_request,
2680        .elevator_former_req_fn = elv_rb_former_request,
2681        .elevator_latter_req_fn = elv_rb_latter_request,
2682        .elevator_set_req_fn = cfq_set_request,
2683        .elevator_put_req_fn = cfq_put_request,
2684        .elevator_may_queue_fn = cfq_may_queue,
2685        .elevator_init_fn = cfq_init_queue,
2686        .elevator_exit_fn = cfq_exit_queue,
2687        .trim = cfq_free_io_context,
2688    },
2689    .elevator_attrs = cfq_attrs,
2690    .elevator_name = "cfq",
2691    .elevator_owner = THIS_MODULE,
2692};
2693
2694static int __init cfq_init(void)
2695{
2696    /*
2697     * could be 0 on HZ < 1000 setups
2698     */
2699    if (!cfq_slice_async)
2700        cfq_slice_async = 1;
2701    if (!cfq_slice_idle)
2702        cfq_slice_idle = 1;
2703
2704    if (cfq_slab_setup())
2705        return -ENOMEM;
2706
2707    elv_register(&iosched_cfq);
2708
2709    return 0;
2710}
2711
2712static void __exit cfq_exit(void)
2713{
2714    DECLARE_COMPLETION_ONSTACK(all_gone);
2715    elv_unregister(&iosched_cfq);
2716    ioc_gone = &all_gone;
2717    /* ioc_gone's update must be visible before reading ioc_count */
2718    smp_wmb();
2719
2720    /*
2721     * this also protects us from entering cfq_slab_kill() with
2722     * pending RCU callbacks
2723     */
2724    if (elv_ioc_count_read(cfq_ioc_count))
2725        wait_for_completion(&all_gone);
2726    cfq_slab_kill();
2727}
2728
2729module_init(cfq_init);
2730module_exit(cfq_exit);
2731
2732MODULE_AUTHOR("Jens Axboe");
2733MODULE_LICENSE("GPL");
2734MODULE_DESCRIPTION("Completely Fair Queueing IO scheduler");
2735

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