Root/mm/slob.c

1/*
2 * SLOB Allocator: Simple List Of Blocks
3 *
4 * Matt Mackall <mpm@selenic.com> 12/30/03
5 *
6 * NUMA support by Paul Mundt, 2007.
7 *
8 * How SLOB works:
9 *
10 * The core of SLOB is a traditional K&R style heap allocator, with
11 * support for returning aligned objects. The granularity of this
12 * allocator is as little as 2 bytes, however typically most architectures
13 * will require 4 bytes on 32-bit and 8 bytes on 64-bit.
14 *
15 * The slob heap is a set of linked list of pages from alloc_pages(),
16 * and within each page, there is a singly-linked list of free blocks
17 * (slob_t). The heap is grown on demand. To reduce fragmentation,
18 * heap pages are segregated into three lists, with objects less than
19 * 256 bytes, objects less than 1024 bytes, and all other objects.
20 *
21 * Allocation from heap involves first searching for a page with
22 * sufficient free blocks (using a next-fit-like approach) followed by
23 * a first-fit scan of the page. Deallocation inserts objects back
24 * into the free list in address order, so this is effectively an
25 * address-ordered first fit.
26 *
27 * Above this is an implementation of kmalloc/kfree. Blocks returned
28 * from kmalloc are prepended with a 4-byte header with the kmalloc size.
29 * If kmalloc is asked for objects of PAGE_SIZE or larger, it calls
30 * alloc_pages() directly, allocating compound pages so the page order
31 * does not have to be separately tracked, and also stores the exact
32 * allocation size in page->private so that it can be used to accurately
33 * provide ksize(). These objects are detected in kfree() because slob_page()
34 * is false for them.
35 *
36 * SLAB is emulated on top of SLOB by simply calling constructors and
37 * destructors for every SLAB allocation. Objects are returned with the
38 * 4-byte alignment unless the SLAB_HWCACHE_ALIGN flag is set, in which
39 * case the low-level allocator will fragment blocks to create the proper
40 * alignment. Again, objects of page-size or greater are allocated by
41 * calling alloc_pages(). As SLAB objects know their size, no separate
42 * size bookkeeping is necessary and there is essentially no allocation
43 * space overhead, and compound pages aren't needed for multi-page
44 * allocations.
45 *
46 * NUMA support in SLOB is fairly simplistic, pushing most of the real
47 * logic down to the page allocator, and simply doing the node accounting
48 * on the upper levels. In the event that a node id is explicitly
49 * provided, alloc_pages_exact_node() with the specified node id is used
50 * instead. The common case (or when the node id isn't explicitly provided)
51 * will default to the current node, as per numa_node_id().
52 *
53 * Node aware pages are still inserted in to the global freelist, and
54 * these are scanned for by matching against the node id encoded in the
55 * page flags. As a result, block allocations that can be satisfied from
56 * the freelist will only be done so on pages residing on the same node,
57 * in order to prevent random node placement.
58 */
59
60#include <linux/kernel.h>
61#include <linux/slab.h>
62#include <linux/mm.h>
63#include <linux/swap.h> /* struct reclaim_state */
64#include <linux/cache.h>
65#include <linux/init.h>
66#include <linux/module.h>
67#include <linux/rcupdate.h>
68#include <linux/list.h>
69#include <linux/kmemleak.h>
70
71#include <trace/events/kmem.h>
72
73#include <asm/atomic.h>
74
75/*
76 * slob_block has a field 'units', which indicates size of block if +ve,
77 * or offset of next block if -ve (in SLOB_UNITs).
78 *
79 * Free blocks of size 1 unit simply contain the offset of the next block.
80 * Those with larger size contain their size in the first SLOB_UNIT of
81 * memory, and the offset of the next free block in the second SLOB_UNIT.
82 */
83#if PAGE_SIZE <= (32767 * 2)
84typedef s16 slobidx_t;
85#else
86typedef s32 slobidx_t;
87#endif
88
89struct slob_block {
90    slobidx_t units;
91};
92typedef struct slob_block slob_t;
93
94/*
95 * We use struct page fields to manage some slob allocation aspects,
96 * however to avoid the horrible mess in include/linux/mm_types.h, we'll
97 * just define our own struct page type variant here.
98 */
99struct slob_page {
100    union {
101        struct {
102            unsigned long flags; /* mandatory */
103            atomic_t _count; /* mandatory */
104            slobidx_t units; /* free units left in page */
105            unsigned long pad[2];
106            slob_t *free; /* first free slob_t in page */
107            struct list_head list; /* linked list of free pages */
108        };
109        struct page page;
110    };
111};
112static inline void struct_slob_page_wrong_size(void)
113{ BUILD_BUG_ON(sizeof(struct slob_page) != sizeof(struct page)); }
114
115/*
116 * free_slob_page: call before a slob_page is returned to the page allocator.
117 */
118static inline void free_slob_page(struct slob_page *sp)
119{
120    reset_page_mapcount(&sp->page);
121    sp->page.mapping = NULL;
122}
123
124/*
125 * All partially free slob pages go on these lists.
126 */
127#define SLOB_BREAK1 256
128#define SLOB_BREAK2 1024
129static LIST_HEAD(free_slob_small);
130static LIST_HEAD(free_slob_medium);
131static LIST_HEAD(free_slob_large);
132
133/*
134 * is_slob_page: True for all slob pages (false for bigblock pages)
135 */
136static inline int is_slob_page(struct slob_page *sp)
137{
138    return PageSlab((struct page *)sp);
139}
140
141static inline void set_slob_page(struct slob_page *sp)
142{
143    __SetPageSlab((struct page *)sp);
144}
145
146static inline void clear_slob_page(struct slob_page *sp)
147{
148    __ClearPageSlab((struct page *)sp);
149}
150
151static inline struct slob_page *slob_page(const void *addr)
152{
153    return (struct slob_page *)virt_to_page(addr);
154}
155
156/*
157 * slob_page_free: true for pages on free_slob_pages list.
158 */
159static inline int slob_page_free(struct slob_page *sp)
160{
161    return PageSlobFree((struct page *)sp);
162}
163
164static void set_slob_page_free(struct slob_page *sp, struct list_head *list)
165{
166    list_add(&sp->list, list);
167    __SetPageSlobFree((struct page *)sp);
168}
169
170static inline void clear_slob_page_free(struct slob_page *sp)
171{
172    list_del(&sp->list);
173    __ClearPageSlobFree((struct page *)sp);
174}
175
176#define SLOB_UNIT sizeof(slob_t)
177#define SLOB_UNITS(size) (((size) + SLOB_UNIT - 1)/SLOB_UNIT)
178#define SLOB_ALIGN L1_CACHE_BYTES
179
180/*
181 * struct slob_rcu is inserted at the tail of allocated slob blocks, which
182 * were created with a SLAB_DESTROY_BY_RCU slab. slob_rcu is used to free
183 * the block using call_rcu.
184 */
185struct slob_rcu {
186    struct rcu_head head;
187    int size;
188};
189
190/*
191 * slob_lock protects all slob allocator structures.
192 */
193static DEFINE_SPINLOCK(slob_lock);
194
195/*
196 * Encode the given size and next info into a free slob block s.
197 */
198static void set_slob(slob_t *s, slobidx_t size, slob_t *next)
199{
200    slob_t *base = (slob_t *)((unsigned long)s & PAGE_MASK);
201    slobidx_t offset = next - base;
202
203    if (size > 1) {
204        s[0].units = size;
205        s[1].units = offset;
206    } else
207        s[0].units = -offset;
208}
209
210/*
211 * Return the size of a slob block.
212 */
213static slobidx_t slob_units(slob_t *s)
214{
215    if (s->units > 0)
216        return s->units;
217    return 1;
218}
219
220/*
221 * Return the next free slob block pointer after this one.
222 */
223static slob_t *slob_next(slob_t *s)
224{
225    slob_t *base = (slob_t *)((unsigned long)s & PAGE_MASK);
226    slobidx_t next;
227
228    if (s[0].units < 0)
229        next = -s[0].units;
230    else
231        next = s[1].units;
232    return base+next;
233}
234
235/*
236 * Returns true if s is the last free block in its page.
237 */
238static int slob_last(slob_t *s)
239{
240    return !((unsigned long)slob_next(s) & ~PAGE_MASK);
241}
242
243static void *slob_new_pages(gfp_t gfp, int order, int node)
244{
245    void *page;
246
247#ifdef CONFIG_NUMA
248    if (node != -1)
249        page = alloc_pages_exact_node(node, gfp, order);
250    else
251#endif
252        page = alloc_pages(gfp, order);
253
254    if (!page)
255        return NULL;
256
257    return page_address(page);
258}
259
260static void slob_free_pages(void *b, int order)
261{
262    if (current->reclaim_state)
263        current->reclaim_state->reclaimed_slab += 1 << order;
264    free_pages((unsigned long)b, order);
265}
266
267/*
268 * Allocate a slob block within a given slob_page sp.
269 */
270static void *slob_page_alloc(struct slob_page *sp, size_t size, int align)
271{
272    slob_t *prev, *cur, *aligned = NULL;
273    int delta = 0, units = SLOB_UNITS(size);
274
275    for (prev = NULL, cur = sp->free; ; prev = cur, cur = slob_next(cur)) {
276        slobidx_t avail = slob_units(cur);
277
278        if (align) {
279            aligned = (slob_t *)ALIGN((unsigned long)cur, align);
280            delta = aligned - cur;
281        }
282        if (avail >= units + delta) { /* room enough? */
283            slob_t *next;
284
285            if (delta) { /* need to fragment head to align? */
286                next = slob_next(cur);
287                set_slob(aligned, avail - delta, next);
288                set_slob(cur, delta, aligned);
289                prev = cur;
290                cur = aligned;
291                avail = slob_units(cur);
292            }
293
294            next = slob_next(cur);
295            if (avail == units) { /* exact fit? unlink. */
296                if (prev)
297                    set_slob(prev, slob_units(prev), next);
298                else
299                    sp->free = next;
300            } else { /* fragment */
301                if (prev)
302                    set_slob(prev, slob_units(prev), cur + units);
303                else
304                    sp->free = cur + units;
305                set_slob(cur + units, avail - units, next);
306            }
307
308            sp->units -= units;
309            if (!sp->units)
310                clear_slob_page_free(sp);
311            return cur;
312        }
313        if (slob_last(cur))
314            return NULL;
315    }
316}
317
318/*
319 * slob_alloc: entry point into the slob allocator.
320 */
321static void *slob_alloc(size_t size, gfp_t gfp, int align, int node)
322{
323    struct slob_page *sp;
324    struct list_head *prev;
325    struct list_head *slob_list;
326    slob_t *b = NULL;
327    unsigned long flags;
328
329    if (size < SLOB_BREAK1)
330        slob_list = &free_slob_small;
331    else if (size < SLOB_BREAK2)
332        slob_list = &free_slob_medium;
333    else
334        slob_list = &free_slob_large;
335
336    spin_lock_irqsave(&slob_lock, flags);
337    /* Iterate through each partially free page, try to find room */
338    list_for_each_entry(sp, slob_list, list) {
339#ifdef CONFIG_NUMA
340        /*
341         * If there's a node specification, search for a partial
342         * page with a matching node id in the freelist.
343         */
344        if (node != -1 && page_to_nid(&sp->page) != node)
345            continue;
346#endif
347        /* Enough room on this page? */
348        if (sp->units < SLOB_UNITS(size))
349            continue;
350
351        /* Attempt to alloc */
352        prev = sp->list.prev;
353        b = slob_page_alloc(sp, size, align);
354        if (!b)
355            continue;
356
357        /* Improve fragment distribution and reduce our average
358         * search time by starting our next search here. (see
359         * Knuth vol 1, sec 2.5, pg 449) */
360        if (prev != slob_list->prev &&
361                slob_list->next != prev->next)
362            list_move_tail(slob_list, prev->next);
363        break;
364    }
365    spin_unlock_irqrestore(&slob_lock, flags);
366
367    /* Not enough space: must allocate a new page */
368    if (!b) {
369        b = slob_new_pages(gfp & ~__GFP_ZERO, 0, node);
370        if (!b)
371            return NULL;
372        sp = slob_page(b);
373        set_slob_page(sp);
374
375        spin_lock_irqsave(&slob_lock, flags);
376        sp->units = SLOB_UNITS(PAGE_SIZE);
377        sp->free = b;
378        INIT_LIST_HEAD(&sp->list);
379        set_slob(b, SLOB_UNITS(PAGE_SIZE), b + SLOB_UNITS(PAGE_SIZE));
380        set_slob_page_free(sp, slob_list);
381        b = slob_page_alloc(sp, size, align);
382        BUG_ON(!b);
383        spin_unlock_irqrestore(&slob_lock, flags);
384    }
385    if (unlikely((gfp & __GFP_ZERO) && b))
386        memset(b, 0, size);
387    return b;
388}
389
390/*
391 * slob_free: entry point into the slob allocator.
392 */
393static void slob_free(void *block, int size)
394{
395    struct slob_page *sp;
396    slob_t *prev, *next, *b = (slob_t *)block;
397    slobidx_t units;
398    unsigned long flags;
399    struct list_head *slob_list;
400
401    if (unlikely(ZERO_OR_NULL_PTR(block)))
402        return;
403    BUG_ON(!size);
404
405    sp = slob_page(block);
406    units = SLOB_UNITS(size);
407
408    spin_lock_irqsave(&slob_lock, flags);
409
410    if (sp->units + units == SLOB_UNITS(PAGE_SIZE)) {
411        /* Go directly to page allocator. Do not pass slob allocator */
412        if (slob_page_free(sp))
413            clear_slob_page_free(sp);
414        spin_unlock_irqrestore(&slob_lock, flags);
415        clear_slob_page(sp);
416        free_slob_page(sp);
417        slob_free_pages(b, 0);
418        return;
419    }
420
421    if (!slob_page_free(sp)) {
422        /* This slob page is about to become partially free. Easy! */
423        sp->units = units;
424        sp->free = b;
425        set_slob(b, units,
426            (void *)((unsigned long)(b +
427                    SLOB_UNITS(PAGE_SIZE)) & PAGE_MASK));
428        if (size < SLOB_BREAK1)
429            slob_list = &free_slob_small;
430        else if (size < SLOB_BREAK2)
431            slob_list = &free_slob_medium;
432        else
433            slob_list = &free_slob_large;
434        set_slob_page_free(sp, slob_list);
435        goto out;
436    }
437
438    /*
439     * Otherwise the page is already partially free, so find reinsertion
440     * point.
441     */
442    sp->units += units;
443
444    if (b < sp->free) {
445        if (b + units == sp->free) {
446            units += slob_units(sp->free);
447            sp->free = slob_next(sp->free);
448        }
449        set_slob(b, units, sp->free);
450        sp->free = b;
451    } else {
452        prev = sp->free;
453        next = slob_next(prev);
454        while (b > next) {
455            prev = next;
456            next = slob_next(prev);
457        }
458
459        if (!slob_last(prev) && b + units == next) {
460            units += slob_units(next);
461            set_slob(b, units, slob_next(next));
462        } else
463            set_slob(b, units, next);
464
465        if (prev + slob_units(prev) == b) {
466            units = slob_units(b) + slob_units(prev);
467            set_slob(prev, units, slob_next(b));
468        } else
469            set_slob(prev, slob_units(prev), b);
470    }
471out:
472    spin_unlock_irqrestore(&slob_lock, flags);
473}
474
475/*
476 * End of slob allocator proper. Begin kmem_cache_alloc and kmalloc frontend.
477 */
478
479void *__kmalloc_node(size_t size, gfp_t gfp, int node)
480{
481    unsigned int *m;
482    int align = max(ARCH_KMALLOC_MINALIGN, ARCH_SLAB_MINALIGN);
483    void *ret;
484
485    lockdep_trace_alloc(gfp);
486
487    if (size < PAGE_SIZE - align) {
488        if (!size)
489            return ZERO_SIZE_PTR;
490
491        m = slob_alloc(size + align, gfp, align, node);
492
493        if (!m)
494            return NULL;
495        *m = size;
496        ret = (void *)m + align;
497
498        trace_kmalloc_node(_RET_IP_, ret,
499                   size, size + align, gfp, node);
500    } else {
501        unsigned int order = get_order(size);
502
503        if (likely(order))
504            gfp |= __GFP_COMP;
505        ret = slob_new_pages(gfp, order, node);
506        if (ret) {
507            struct page *page;
508            page = virt_to_page(ret);
509            page->private = size;
510        }
511
512        trace_kmalloc_node(_RET_IP_, ret,
513                   size, PAGE_SIZE << order, gfp, node);
514    }
515
516    kmemleak_alloc(ret, size, 1, gfp);
517    return ret;
518}
519EXPORT_SYMBOL(__kmalloc_node);
520
521void kfree(const void *block)
522{
523    struct slob_page *sp;
524
525    trace_kfree(_RET_IP_, block);
526
527    if (unlikely(ZERO_OR_NULL_PTR(block)))
528        return;
529    kmemleak_free(block);
530
531    sp = slob_page(block);
532    if (is_slob_page(sp)) {
533        int align = max(ARCH_KMALLOC_MINALIGN, ARCH_SLAB_MINALIGN);
534        unsigned int *m = (unsigned int *)(block - align);
535        slob_free(m, *m + align);
536    } else
537        put_page(&sp->page);
538}
539EXPORT_SYMBOL(kfree);
540
541/* can't use ksize for kmem_cache_alloc memory, only kmalloc */
542size_t ksize(const void *block)
543{
544    struct slob_page *sp;
545
546    BUG_ON(!block);
547    if (unlikely(block == ZERO_SIZE_PTR))
548        return 0;
549
550    sp = slob_page(block);
551    if (is_slob_page(sp)) {
552        int align = max(ARCH_KMALLOC_MINALIGN, ARCH_SLAB_MINALIGN);
553        unsigned int *m = (unsigned int *)(block - align);
554        return SLOB_UNITS(*m) * SLOB_UNIT;
555    } else
556        return sp->page.private;
557}
558EXPORT_SYMBOL(ksize);
559
560struct kmem_cache {
561    unsigned int size, align;
562    unsigned long flags;
563    const char *name;
564    void (*ctor)(void *);
565};
566
567struct kmem_cache *kmem_cache_create(const char *name, size_t size,
568    size_t align, unsigned long flags, void (*ctor)(void *))
569{
570    struct kmem_cache *c;
571
572    c = slob_alloc(sizeof(struct kmem_cache),
573        GFP_KERNEL, ARCH_KMALLOC_MINALIGN, -1);
574
575    if (c) {
576        c->name = name;
577        c->size = size;
578        if (flags & SLAB_DESTROY_BY_RCU) {
579            /* leave room for rcu footer at the end of object */
580            c->size += sizeof(struct slob_rcu);
581        }
582        c->flags = flags;
583        c->ctor = ctor;
584        /* ignore alignment unless it's forced */
585        c->align = (flags & SLAB_HWCACHE_ALIGN) ? SLOB_ALIGN : 0;
586        if (c->align < ARCH_SLAB_MINALIGN)
587            c->align = ARCH_SLAB_MINALIGN;
588        if (c->align < align)
589            c->align = align;
590    } else if (flags & SLAB_PANIC)
591        panic("Cannot create slab cache %s\n", name);
592
593    kmemleak_alloc(c, sizeof(struct kmem_cache), 1, GFP_KERNEL);
594    return c;
595}
596EXPORT_SYMBOL(kmem_cache_create);
597
598void kmem_cache_destroy(struct kmem_cache *c)
599{
600    kmemleak_free(c);
601    if (c->flags & SLAB_DESTROY_BY_RCU)
602        rcu_barrier();
603    slob_free(c, sizeof(struct kmem_cache));
604}
605EXPORT_SYMBOL(kmem_cache_destroy);
606
607void *kmem_cache_alloc_node(struct kmem_cache *c, gfp_t flags, int node)
608{
609    void *b;
610
611    if (c->size < PAGE_SIZE) {
612        b = slob_alloc(c->size, flags, c->align, node);
613        trace_kmem_cache_alloc_node(_RET_IP_, b, c->size,
614                        SLOB_UNITS(c->size) * SLOB_UNIT,
615                        flags, node);
616    } else {
617        b = slob_new_pages(flags, get_order(c->size), node);
618        trace_kmem_cache_alloc_node(_RET_IP_, b, c->size,
619                        PAGE_SIZE << get_order(c->size),
620                        flags, node);
621    }
622
623    if (c->ctor)
624        c->ctor(b);
625
626    kmemleak_alloc_recursive(b, c->size, 1, c->flags, flags);
627    return b;
628}
629EXPORT_SYMBOL(kmem_cache_alloc_node);
630
631static void __kmem_cache_free(void *b, int size)
632{
633    if (size < PAGE_SIZE)
634        slob_free(b, size);
635    else
636        slob_free_pages(b, get_order(size));
637}
638
639static void kmem_rcu_free(struct rcu_head *head)
640{
641    struct slob_rcu *slob_rcu = (struct slob_rcu *)head;
642    void *b = (void *)slob_rcu - (slob_rcu->size - sizeof(struct slob_rcu));
643
644    __kmem_cache_free(b, slob_rcu->size);
645}
646
647void kmem_cache_free(struct kmem_cache *c, void *b)
648{
649    kmemleak_free_recursive(b, c->flags);
650    if (unlikely(c->flags & SLAB_DESTROY_BY_RCU)) {
651        struct slob_rcu *slob_rcu;
652        slob_rcu = b + (c->size - sizeof(struct slob_rcu));
653        slob_rcu->size = c->size;
654        call_rcu(&slob_rcu->head, kmem_rcu_free);
655    } else {
656        __kmem_cache_free(b, c->size);
657    }
658
659    trace_kmem_cache_free(_RET_IP_, b);
660}
661EXPORT_SYMBOL(kmem_cache_free);
662
663unsigned int kmem_cache_size(struct kmem_cache *c)
664{
665    return c->size;
666}
667EXPORT_SYMBOL(kmem_cache_size);
668
669int kmem_cache_shrink(struct kmem_cache *d)
670{
671    return 0;
672}
673EXPORT_SYMBOL(kmem_cache_shrink);
674
675static unsigned int slob_ready __read_mostly;
676
677int slab_is_available(void)
678{
679    return slob_ready;
680}
681
682void __init kmem_cache_init(void)
683{
684    slob_ready = 1;
685}
686
687void __init kmem_cache_init_late(void)
688{
689    /* Nothing to do */
690}
691

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