Root/mm/zswap.c

1/*
2 * zswap.c - zswap driver file
3 *
4 * zswap is a backend for frontswap that takes pages that are in the process
5 * of being swapped out and attempts to compress and store them in a
6 * RAM-based memory pool. This can result in a significant I/O reduction on
7 * the swap device and, in the case where decompressing from RAM is faster
8 * than reading from the swap device, can also improve workload performance.
9 *
10 * Copyright (C) 2012 Seth Jennings <sjenning@linux.vnet.ibm.com>
11 *
12 * This program is free software; you can redistribute it and/or
13 * modify it under the terms of the GNU General Public License
14 * as published by the Free Software Foundation; either version 2
15 * of the License, or (at your option) any later version.
16 *
17 * This program is distributed in the hope that it will be useful,
18 * but WITHOUT ANY WARRANTY; without even the implied warranty of
19 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
20 * GNU General Public License for more details.
21*/
22
23#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
24
25#include <linux/module.h>
26#include <linux/cpu.h>
27#include <linux/highmem.h>
28#include <linux/slab.h>
29#include <linux/spinlock.h>
30#include <linux/types.h>
31#include <linux/atomic.h>
32#include <linux/frontswap.h>
33#include <linux/rbtree.h>
34#include <linux/swap.h>
35#include <linux/crypto.h>
36#include <linux/mempool.h>
37#include <linux/zbud.h>
38
39#include <linux/mm_types.h>
40#include <linux/page-flags.h>
41#include <linux/swapops.h>
42#include <linux/writeback.h>
43#include <linux/pagemap.h>
44
45/*********************************
46* statistics
47**********************************/
48/* Number of memory pages used by the compressed pool */
49static u64 zswap_pool_pages;
50/* The number of compressed pages currently stored in zswap */
51static atomic_t zswap_stored_pages = ATOMIC_INIT(0);
52
53/*
54 * The statistics below are not protected from concurrent access for
55 * performance reasons so they may not be a 100% accurate. However,
56 * they do provide useful information on roughly how many times a
57 * certain event is occurring.
58*/
59
60/* Pool limit was hit (see zswap_max_pool_percent) */
61static u64 zswap_pool_limit_hit;
62/* Pages written back when pool limit was reached */
63static u64 zswap_written_back_pages;
64/* Store failed due to a reclaim failure after pool limit was reached */
65static u64 zswap_reject_reclaim_fail;
66/* Compressed page was too big for the allocator to (optimally) store */
67static u64 zswap_reject_compress_poor;
68/* Store failed because underlying allocator could not get memory */
69static u64 zswap_reject_alloc_fail;
70/* Store failed because the entry metadata could not be allocated (rare) */
71static u64 zswap_reject_kmemcache_fail;
72/* Duplicate store was encountered (rare) */
73static u64 zswap_duplicate_entry;
74
75/*********************************
76* tunables
77**********************************/
78/* Enable/disable zswap (disabled by default, fixed at boot for now) */
79static bool zswap_enabled __read_mostly;
80module_param_named(enabled, zswap_enabled, bool, 0444);
81
82/* Compressor to be used by zswap (fixed at boot for now) */
83#define ZSWAP_COMPRESSOR_DEFAULT "lzo"
84static char *zswap_compressor = ZSWAP_COMPRESSOR_DEFAULT;
85module_param_named(compressor, zswap_compressor, charp, 0444);
86
87/* The maximum percentage of memory that the compressed pool can occupy */
88static unsigned int zswap_max_pool_percent = 20;
89module_param_named(max_pool_percent,
90            zswap_max_pool_percent, uint, 0644);
91
92/* zbud_pool is shared by all of zswap backend */
93static struct zbud_pool *zswap_pool;
94
95/*********************************
96* compression functions
97**********************************/
98/* per-cpu compression transforms */
99static struct crypto_comp * __percpu *zswap_comp_pcpu_tfms;
100
101enum comp_op {
102    ZSWAP_COMPOP_COMPRESS,
103    ZSWAP_COMPOP_DECOMPRESS
104};
105
106static int zswap_comp_op(enum comp_op op, const u8 *src, unsigned int slen,
107                u8 *dst, unsigned int *dlen)
108{
109    struct crypto_comp *tfm;
110    int ret;
111
112    tfm = *per_cpu_ptr(zswap_comp_pcpu_tfms, get_cpu());
113    switch (op) {
114    case ZSWAP_COMPOP_COMPRESS:
115        ret = crypto_comp_compress(tfm, src, slen, dst, dlen);
116        break;
117    case ZSWAP_COMPOP_DECOMPRESS:
118        ret = crypto_comp_decompress(tfm, src, slen, dst, dlen);
119        break;
120    default:
121        ret = -EINVAL;
122    }
123
124    put_cpu();
125    return ret;
126}
127
128static int __init zswap_comp_init(void)
129{
130    if (!crypto_has_comp(zswap_compressor, 0, 0)) {
131        pr_info("%s compressor not available\n", zswap_compressor);
132        /* fall back to default compressor */
133        zswap_compressor = ZSWAP_COMPRESSOR_DEFAULT;
134        if (!crypto_has_comp(zswap_compressor, 0, 0))
135            /* can't even load the default compressor */
136            return -ENODEV;
137    }
138    pr_info("using %s compressor\n", zswap_compressor);
139
140    /* alloc percpu transforms */
141    zswap_comp_pcpu_tfms = alloc_percpu(struct crypto_comp *);
142    if (!zswap_comp_pcpu_tfms)
143        return -ENOMEM;
144    return 0;
145}
146
147static void zswap_comp_exit(void)
148{
149    /* free percpu transforms */
150    if (zswap_comp_pcpu_tfms)
151        free_percpu(zswap_comp_pcpu_tfms);
152}
153
154/*********************************
155* data structures
156**********************************/
157/*
158 * struct zswap_entry
159 *
160 * This structure contains the metadata for tracking a single compressed
161 * page within zswap.
162 *
163 * rbnode - links the entry into red-black tree for the appropriate swap type
164 * refcount - the number of outstanding reference to the entry. This is needed
165 * to protect against premature freeing of the entry by code
166 * concurrent calls to load, invalidate, and writeback. The lock
167 * for the zswap_tree structure that contains the entry must
168 * be held while changing the refcount. Since the lock must
169 * be held, there is no reason to also make refcount atomic.
170 * offset - the swap offset for the entry. Index into the red-black tree.
171 * handle - zbud allocation handle that stores the compressed page data
172 * length - the length in bytes of the compressed page data. Needed during
173 * decompression
174 */
175struct zswap_entry {
176    struct rb_node rbnode;
177    pgoff_t offset;
178    int refcount;
179    unsigned int length;
180    unsigned long handle;
181};
182
183struct zswap_header {
184    swp_entry_t swpentry;
185};
186
187/*
188 * The tree lock in the zswap_tree struct protects a few things:
189 * - the rbtree
190 * - the refcount field of each entry in the tree
191 */
192struct zswap_tree {
193    struct rb_root rbroot;
194    spinlock_t lock;
195};
196
197static struct zswap_tree *zswap_trees[MAX_SWAPFILES];
198
199/*********************************
200* zswap entry functions
201**********************************/
202static struct kmem_cache *zswap_entry_cache;
203
204static int zswap_entry_cache_create(void)
205{
206    zswap_entry_cache = KMEM_CACHE(zswap_entry, 0);
207    return zswap_entry_cache == NULL;
208}
209
210static void zswap_entry_cache_destory(void)
211{
212    kmem_cache_destroy(zswap_entry_cache);
213}
214
215static struct zswap_entry *zswap_entry_cache_alloc(gfp_t gfp)
216{
217    struct zswap_entry *entry;
218    entry = kmem_cache_alloc(zswap_entry_cache, gfp);
219    if (!entry)
220        return NULL;
221    entry->refcount = 1;
222    RB_CLEAR_NODE(&entry->rbnode);
223    return entry;
224}
225
226static void zswap_entry_cache_free(struct zswap_entry *entry)
227{
228    kmem_cache_free(zswap_entry_cache, entry);
229}
230
231/*********************************
232* rbtree functions
233**********************************/
234static struct zswap_entry *zswap_rb_search(struct rb_root *root, pgoff_t offset)
235{
236    struct rb_node *node = root->rb_node;
237    struct zswap_entry *entry;
238
239    while (node) {
240        entry = rb_entry(node, struct zswap_entry, rbnode);
241        if (entry->offset > offset)
242            node = node->rb_left;
243        else if (entry->offset < offset)
244            node = node->rb_right;
245        else
246            return entry;
247    }
248    return NULL;
249}
250
251/*
252 * In the case that a entry with the same offset is found, a pointer to
253 * the existing entry is stored in dupentry and the function returns -EEXIST
254 */
255static int zswap_rb_insert(struct rb_root *root, struct zswap_entry *entry,
256            struct zswap_entry **dupentry)
257{
258    struct rb_node **link = &root->rb_node, *parent = NULL;
259    struct zswap_entry *myentry;
260
261    while (*link) {
262        parent = *link;
263        myentry = rb_entry(parent, struct zswap_entry, rbnode);
264        if (myentry->offset > entry->offset)
265            link = &(*link)->rb_left;
266        else if (myentry->offset < entry->offset)
267            link = &(*link)->rb_right;
268        else {
269            *dupentry = myentry;
270            return -EEXIST;
271        }
272    }
273    rb_link_node(&entry->rbnode, parent, link);
274    rb_insert_color(&entry->rbnode, root);
275    return 0;
276}
277
278static void zswap_rb_erase(struct rb_root *root, struct zswap_entry *entry)
279{
280    if (!RB_EMPTY_NODE(&entry->rbnode)) {
281        rb_erase(&entry->rbnode, root);
282        RB_CLEAR_NODE(&entry->rbnode);
283    }
284}
285
286/*
287 * Carries out the common pattern of freeing and entry's zbud allocation,
288 * freeing the entry itself, and decrementing the number of stored pages.
289 */
290static void zswap_free_entry(struct zswap_entry *entry)
291{
292    zbud_free(zswap_pool, entry->handle);
293    zswap_entry_cache_free(entry);
294    atomic_dec(&zswap_stored_pages);
295    zswap_pool_pages = zbud_get_pool_size(zswap_pool);
296}
297
298/* caller must hold the tree lock */
299static void zswap_entry_get(struct zswap_entry *entry)
300{
301    entry->refcount++;
302}
303
304/* caller must hold the tree lock
305* remove from the tree and free it, if nobody reference the entry
306*/
307static void zswap_entry_put(struct zswap_tree *tree,
308            struct zswap_entry *entry)
309{
310    int refcount = --entry->refcount;
311
312    BUG_ON(refcount < 0);
313    if (refcount == 0) {
314        zswap_rb_erase(&tree->rbroot, entry);
315        zswap_free_entry(entry);
316    }
317}
318
319/* caller must hold the tree lock */
320static struct zswap_entry *zswap_entry_find_get(struct rb_root *root,
321                pgoff_t offset)
322{
323    struct zswap_entry *entry = NULL;
324
325    entry = zswap_rb_search(root, offset);
326    if (entry)
327        zswap_entry_get(entry);
328
329    return entry;
330}
331
332/*********************************
333* per-cpu code
334**********************************/
335static DEFINE_PER_CPU(u8 *, zswap_dstmem);
336
337static int __zswap_cpu_notifier(unsigned long action, unsigned long cpu)
338{
339    struct crypto_comp *tfm;
340    u8 *dst;
341
342    switch (action) {
343    case CPU_UP_PREPARE:
344        tfm = crypto_alloc_comp(zswap_compressor, 0, 0);
345        if (IS_ERR(tfm)) {
346            pr_err("can't allocate compressor transform\n");
347            return NOTIFY_BAD;
348        }
349        *per_cpu_ptr(zswap_comp_pcpu_tfms, cpu) = tfm;
350        dst = kmalloc_node(PAGE_SIZE * 2, GFP_KERNEL, cpu_to_node(cpu));
351        if (!dst) {
352            pr_err("can't allocate compressor buffer\n");
353            crypto_free_comp(tfm);
354            *per_cpu_ptr(zswap_comp_pcpu_tfms, cpu) = NULL;
355            return NOTIFY_BAD;
356        }
357        per_cpu(zswap_dstmem, cpu) = dst;
358        break;
359    case CPU_DEAD:
360    case CPU_UP_CANCELED:
361        tfm = *per_cpu_ptr(zswap_comp_pcpu_tfms, cpu);
362        if (tfm) {
363            crypto_free_comp(tfm);
364            *per_cpu_ptr(zswap_comp_pcpu_tfms, cpu) = NULL;
365        }
366        dst = per_cpu(zswap_dstmem, cpu);
367        kfree(dst);
368        per_cpu(zswap_dstmem, cpu) = NULL;
369        break;
370    default:
371        break;
372    }
373    return NOTIFY_OK;
374}
375
376static int zswap_cpu_notifier(struct notifier_block *nb,
377                unsigned long action, void *pcpu)
378{
379    unsigned long cpu = (unsigned long)pcpu;
380    return __zswap_cpu_notifier(action, cpu);
381}
382
383static struct notifier_block zswap_cpu_notifier_block = {
384    .notifier_call = zswap_cpu_notifier
385};
386
387static int zswap_cpu_init(void)
388{
389    unsigned long cpu;
390
391    cpu_notifier_register_begin();
392    for_each_online_cpu(cpu)
393        if (__zswap_cpu_notifier(CPU_UP_PREPARE, cpu) != NOTIFY_OK)
394            goto cleanup;
395    __register_cpu_notifier(&zswap_cpu_notifier_block);
396    cpu_notifier_register_done();
397    return 0;
398
399cleanup:
400    for_each_online_cpu(cpu)
401        __zswap_cpu_notifier(CPU_UP_CANCELED, cpu);
402    cpu_notifier_register_done();
403    return -ENOMEM;
404}
405
406/*********************************
407* helpers
408**********************************/
409static bool zswap_is_full(void)
410{
411    return totalram_pages * zswap_max_pool_percent / 100 <
412        zswap_pool_pages;
413}
414
415/*********************************
416* writeback code
417**********************************/
418/* return enum for zswap_get_swap_cache_page */
419enum zswap_get_swap_ret {
420    ZSWAP_SWAPCACHE_NEW,
421    ZSWAP_SWAPCACHE_EXIST,
422    ZSWAP_SWAPCACHE_FAIL,
423};
424
425/*
426 * zswap_get_swap_cache_page
427 *
428 * This is an adaption of read_swap_cache_async()
429 *
430 * This function tries to find a page with the given swap entry
431 * in the swapper_space address space (the swap cache). If the page
432 * is found, it is returned in retpage. Otherwise, a page is allocated,
433 * added to the swap cache, and returned in retpage.
434 *
435 * If success, the swap cache page is returned in retpage
436 * Returns ZSWAP_SWAPCACHE_EXIST if page was already in the swap cache
437 * Returns ZSWAP_SWAPCACHE_NEW if the new page needs to be populated,
438 * the new page is added to swapcache and locked
439 * Returns ZSWAP_SWAPCACHE_FAIL on error
440 */
441static int zswap_get_swap_cache_page(swp_entry_t entry,
442                struct page **retpage)
443{
444    struct page *found_page, *new_page = NULL;
445    struct address_space *swapper_space = swap_address_space(entry);
446    int err;
447
448    *retpage = NULL;
449    do {
450        /*
451         * First check the swap cache. Since this is normally
452         * called after lookup_swap_cache() failed, re-calling
453         * that would confuse statistics.
454         */
455        found_page = find_get_page(swapper_space, entry.val);
456        if (found_page)
457            break;
458
459        /*
460         * Get a new page to read into from swap.
461         */
462        if (!new_page) {
463            new_page = alloc_page(GFP_KERNEL);
464            if (!new_page)
465                break; /* Out of memory */
466        }
467
468        /*
469         * call radix_tree_preload() while we can wait.
470         */
471        err = radix_tree_preload(GFP_KERNEL);
472        if (err)
473            break;
474
475        /*
476         * Swap entry may have been freed since our caller observed it.
477         */
478        err = swapcache_prepare(entry);
479        if (err == -EEXIST) { /* seems racy */
480            radix_tree_preload_end();
481            continue;
482        }
483        if (err) { /* swp entry is obsolete ? */
484            radix_tree_preload_end();
485            break;
486        }
487
488        /* May fail (-ENOMEM) if radix-tree node allocation failed. */
489        __set_page_locked(new_page);
490        SetPageSwapBacked(new_page);
491        err = __add_to_swap_cache(new_page, entry);
492        if (likely(!err)) {
493            radix_tree_preload_end();
494            lru_cache_add_anon(new_page);
495            *retpage = new_page;
496            return ZSWAP_SWAPCACHE_NEW;
497        }
498        radix_tree_preload_end();
499        ClearPageSwapBacked(new_page);
500        __clear_page_locked(new_page);
501        /*
502         * add_to_swap_cache() doesn't return -EEXIST, so we can safely
503         * clear SWAP_HAS_CACHE flag.
504         */
505        swapcache_free(entry, NULL);
506    } while (err != -ENOMEM);
507
508    if (new_page)
509        page_cache_release(new_page);
510    if (!found_page)
511        return ZSWAP_SWAPCACHE_FAIL;
512    *retpage = found_page;
513    return ZSWAP_SWAPCACHE_EXIST;
514}
515
516/*
517 * Attempts to free an entry by adding a page to the swap cache,
518 * decompressing the entry data into the page, and issuing a
519 * bio write to write the page back to the swap device.
520 *
521 * This can be thought of as a "resumed writeback" of the page
522 * to the swap device. We are basically resuming the same swap
523 * writeback path that was intercepted with the frontswap_store()
524 * in the first place. After the page has been decompressed into
525 * the swap cache, the compressed version stored by zswap can be
526 * freed.
527 */
528static int zswap_writeback_entry(struct zbud_pool *pool, unsigned long handle)
529{
530    struct zswap_header *zhdr;
531    swp_entry_t swpentry;
532    struct zswap_tree *tree;
533    pgoff_t offset;
534    struct zswap_entry *entry;
535    struct page *page;
536    u8 *src, *dst;
537    unsigned int dlen;
538    int ret;
539    struct writeback_control wbc = {
540        .sync_mode = WB_SYNC_NONE,
541    };
542
543    /* extract swpentry from data */
544    zhdr = zbud_map(pool, handle);
545    swpentry = zhdr->swpentry; /* here */
546    zbud_unmap(pool, handle);
547    tree = zswap_trees[swp_type(swpentry)];
548    offset = swp_offset(swpentry);
549
550    /* find and ref zswap entry */
551    spin_lock(&tree->lock);
552    entry = zswap_entry_find_get(&tree->rbroot, offset);
553    if (!entry) {
554        /* entry was invalidated */
555        spin_unlock(&tree->lock);
556        return 0;
557    }
558    spin_unlock(&tree->lock);
559    BUG_ON(offset != entry->offset);
560
561    /* try to allocate swap cache page */
562    switch (zswap_get_swap_cache_page(swpentry, &page)) {
563    case ZSWAP_SWAPCACHE_FAIL: /* no memory or invalidate happened */
564        ret = -ENOMEM;
565        goto fail;
566
567    case ZSWAP_SWAPCACHE_EXIST:
568        /* page is already in the swap cache, ignore for now */
569        page_cache_release(page);
570        ret = -EEXIST;
571        goto fail;
572
573    case ZSWAP_SWAPCACHE_NEW: /* page is locked */
574        /* decompress */
575        dlen = PAGE_SIZE;
576        src = (u8 *)zbud_map(zswap_pool, entry->handle) +
577            sizeof(struct zswap_header);
578        dst = kmap_atomic(page);
579        ret = zswap_comp_op(ZSWAP_COMPOP_DECOMPRESS, src,
580                entry->length, dst, &dlen);
581        kunmap_atomic(dst);
582        zbud_unmap(zswap_pool, entry->handle);
583        BUG_ON(ret);
584        BUG_ON(dlen != PAGE_SIZE);
585
586        /* page is up to date */
587        SetPageUptodate(page);
588    }
589
590    /* move it to the tail of the inactive list after end_writeback */
591    SetPageReclaim(page);
592
593    /* start writeback */
594    __swap_writepage(page, &wbc, end_swap_bio_write);
595    page_cache_release(page);
596    zswap_written_back_pages++;
597
598    spin_lock(&tree->lock);
599    /* drop local reference */
600    zswap_entry_put(tree, entry);
601
602    /*
603    * There are two possible situations for entry here:
604    * (1) refcount is 1(normal case), entry is valid and on the tree
605    * (2) refcount is 0, entry is freed and not on the tree
606    * because invalidate happened during writeback
607    * search the tree and free the entry if find entry
608    */
609    if (entry == zswap_rb_search(&tree->rbroot, offset))
610        zswap_entry_put(tree, entry);
611    spin_unlock(&tree->lock);
612
613    goto end;
614
615    /*
616    * if we get here due to ZSWAP_SWAPCACHE_EXIST
617    * a load may happening concurrently
618    * it is safe and okay to not free the entry
619    * if we free the entry in the following put
620    * it it either okay to return !0
621    */
622fail:
623    spin_lock(&tree->lock);
624    zswap_entry_put(tree, entry);
625    spin_unlock(&tree->lock);
626
627end:
628    return ret;
629}
630
631/*********************************
632* frontswap hooks
633**********************************/
634/* attempts to compress and store an single page */
635static int zswap_frontswap_store(unsigned type, pgoff_t offset,
636                struct page *page)
637{
638    struct zswap_tree *tree = zswap_trees[type];
639    struct zswap_entry *entry, *dupentry;
640    int ret;
641    unsigned int dlen = PAGE_SIZE, len;
642    unsigned long handle;
643    char *buf;
644    u8 *src, *dst;
645    struct zswap_header *zhdr;
646
647    if (!tree) {
648        ret = -ENODEV;
649        goto reject;
650    }
651
652    /* reclaim space if needed */
653    if (zswap_is_full()) {
654        zswap_pool_limit_hit++;
655        if (zbud_reclaim_page(zswap_pool, 8)) {
656            zswap_reject_reclaim_fail++;
657            ret = -ENOMEM;
658            goto reject;
659        }
660    }
661
662    /* allocate entry */
663    entry = zswap_entry_cache_alloc(GFP_KERNEL);
664    if (!entry) {
665        zswap_reject_kmemcache_fail++;
666        ret = -ENOMEM;
667        goto reject;
668    }
669
670    /* compress */
671    dst = get_cpu_var(zswap_dstmem);
672    src = kmap_atomic(page);
673    ret = zswap_comp_op(ZSWAP_COMPOP_COMPRESS, src, PAGE_SIZE, dst, &dlen);
674    kunmap_atomic(src);
675    if (ret) {
676        ret = -EINVAL;
677        goto freepage;
678    }
679
680    /* store */
681    len = dlen + sizeof(struct zswap_header);
682    ret = zbud_alloc(zswap_pool, len, __GFP_NORETRY | __GFP_NOWARN,
683        &handle);
684    if (ret == -ENOSPC) {
685        zswap_reject_compress_poor++;
686        goto freepage;
687    }
688    if (ret) {
689        zswap_reject_alloc_fail++;
690        goto freepage;
691    }
692    zhdr = zbud_map(zswap_pool, handle);
693    zhdr->swpentry = swp_entry(type, offset);
694    buf = (u8 *)(zhdr + 1);
695    memcpy(buf, dst, dlen);
696    zbud_unmap(zswap_pool, handle);
697    put_cpu_var(zswap_dstmem);
698
699    /* populate entry */
700    entry->offset = offset;
701    entry->handle = handle;
702    entry->length = dlen;
703
704    /* map */
705    spin_lock(&tree->lock);
706    do {
707        ret = zswap_rb_insert(&tree->rbroot, entry, &dupentry);
708        if (ret == -EEXIST) {
709            zswap_duplicate_entry++;
710            /* remove from rbtree */
711            zswap_rb_erase(&tree->rbroot, dupentry);
712            zswap_entry_put(tree, dupentry);
713        }
714    } while (ret == -EEXIST);
715    spin_unlock(&tree->lock);
716
717    /* update stats */
718    atomic_inc(&zswap_stored_pages);
719    zswap_pool_pages = zbud_get_pool_size(zswap_pool);
720
721    return 0;
722
723freepage:
724    put_cpu_var(zswap_dstmem);
725    zswap_entry_cache_free(entry);
726reject:
727    return ret;
728}
729
730/*
731 * returns 0 if the page was successfully decompressed
732 * return -1 on entry not found or error
733*/
734static int zswap_frontswap_load(unsigned type, pgoff_t offset,
735                struct page *page)
736{
737    struct zswap_tree *tree = zswap_trees[type];
738    struct zswap_entry *entry;
739    u8 *src, *dst;
740    unsigned int dlen;
741    int ret;
742
743    /* find */
744    spin_lock(&tree->lock);
745    entry = zswap_entry_find_get(&tree->rbroot, offset);
746    if (!entry) {
747        /* entry was written back */
748        spin_unlock(&tree->lock);
749        return -1;
750    }
751    spin_unlock(&tree->lock);
752
753    /* decompress */
754    dlen = PAGE_SIZE;
755    src = (u8 *)zbud_map(zswap_pool, entry->handle) +
756            sizeof(struct zswap_header);
757    dst = kmap_atomic(page);
758    ret = zswap_comp_op(ZSWAP_COMPOP_DECOMPRESS, src, entry->length,
759        dst, &dlen);
760    kunmap_atomic(dst);
761    zbud_unmap(zswap_pool, entry->handle);
762    BUG_ON(ret);
763
764    spin_lock(&tree->lock);
765    zswap_entry_put(tree, entry);
766    spin_unlock(&tree->lock);
767
768    return 0;
769}
770
771/* frees an entry in zswap */
772static void zswap_frontswap_invalidate_page(unsigned type, pgoff_t offset)
773{
774    struct zswap_tree *tree = zswap_trees[type];
775    struct zswap_entry *entry;
776
777    /* find */
778    spin_lock(&tree->lock);
779    entry = zswap_rb_search(&tree->rbroot, offset);
780    if (!entry) {
781        /* entry was written back */
782        spin_unlock(&tree->lock);
783        return;
784    }
785
786    /* remove from rbtree */
787    zswap_rb_erase(&tree->rbroot, entry);
788
789    /* drop the initial reference from entry creation */
790    zswap_entry_put(tree, entry);
791
792    spin_unlock(&tree->lock);
793}
794
795/* frees all zswap entries for the given swap type */
796static void zswap_frontswap_invalidate_area(unsigned type)
797{
798    struct zswap_tree *tree = zswap_trees[type];
799    struct zswap_entry *entry, *n;
800
801    if (!tree)
802        return;
803
804    /* walk the tree and free everything */
805    spin_lock(&tree->lock);
806    rbtree_postorder_for_each_entry_safe(entry, n, &tree->rbroot, rbnode)
807        zswap_free_entry(entry);
808    tree->rbroot = RB_ROOT;
809    spin_unlock(&tree->lock);
810    kfree(tree);
811    zswap_trees[type] = NULL;
812}
813
814static struct zbud_ops zswap_zbud_ops = {
815    .evict = zswap_writeback_entry
816};
817
818static void zswap_frontswap_init(unsigned type)
819{
820    struct zswap_tree *tree;
821
822    tree = kzalloc(sizeof(struct zswap_tree), GFP_KERNEL);
823    if (!tree) {
824        pr_err("alloc failed, zswap disabled for swap type %d\n", type);
825        return;
826    }
827
828    tree->rbroot = RB_ROOT;
829    spin_lock_init(&tree->lock);
830    zswap_trees[type] = tree;
831}
832
833static struct frontswap_ops zswap_frontswap_ops = {
834    .store = zswap_frontswap_store,
835    .load = zswap_frontswap_load,
836    .invalidate_page = zswap_frontswap_invalidate_page,
837    .invalidate_area = zswap_frontswap_invalidate_area,
838    .init = zswap_frontswap_init
839};
840
841/*********************************
842* debugfs functions
843**********************************/
844#ifdef CONFIG_DEBUG_FS
845#include <linux/debugfs.h>
846
847static struct dentry *zswap_debugfs_root;
848
849static int __init zswap_debugfs_init(void)
850{
851    if (!debugfs_initialized())
852        return -ENODEV;
853
854    zswap_debugfs_root = debugfs_create_dir("zswap", NULL);
855    if (!zswap_debugfs_root)
856        return -ENOMEM;
857
858    debugfs_create_u64("pool_limit_hit", S_IRUGO,
859            zswap_debugfs_root, &zswap_pool_limit_hit);
860    debugfs_create_u64("reject_reclaim_fail", S_IRUGO,
861            zswap_debugfs_root, &zswap_reject_reclaim_fail);
862    debugfs_create_u64("reject_alloc_fail", S_IRUGO,
863            zswap_debugfs_root, &zswap_reject_alloc_fail);
864    debugfs_create_u64("reject_kmemcache_fail", S_IRUGO,
865            zswap_debugfs_root, &zswap_reject_kmemcache_fail);
866    debugfs_create_u64("reject_compress_poor", S_IRUGO,
867            zswap_debugfs_root, &zswap_reject_compress_poor);
868    debugfs_create_u64("written_back_pages", S_IRUGO,
869            zswap_debugfs_root, &zswap_written_back_pages);
870    debugfs_create_u64("duplicate_entry", S_IRUGO,
871            zswap_debugfs_root, &zswap_duplicate_entry);
872    debugfs_create_u64("pool_pages", S_IRUGO,
873            zswap_debugfs_root, &zswap_pool_pages);
874    debugfs_create_atomic_t("stored_pages", S_IRUGO,
875            zswap_debugfs_root, &zswap_stored_pages);
876
877    return 0;
878}
879
880static void __exit zswap_debugfs_exit(void)
881{
882    debugfs_remove_recursive(zswap_debugfs_root);
883}
884#else
885static int __init zswap_debugfs_init(void)
886{
887    return 0;
888}
889
890static void __exit zswap_debugfs_exit(void) { }
891#endif
892
893/*********************************
894* module init and exit
895**********************************/
896static int __init init_zswap(void)
897{
898    if (!zswap_enabled)
899        return 0;
900
901    pr_info("loading zswap\n");
902
903    zswap_pool = zbud_create_pool(GFP_KERNEL, &zswap_zbud_ops);
904    if (!zswap_pool) {
905        pr_err("zbud pool creation failed\n");
906        goto error;
907    }
908
909    if (zswap_entry_cache_create()) {
910        pr_err("entry cache creation failed\n");
911        goto cachefail;
912    }
913    if (zswap_comp_init()) {
914        pr_err("compressor initialization failed\n");
915        goto compfail;
916    }
917    if (zswap_cpu_init()) {
918        pr_err("per-cpu initialization failed\n");
919        goto pcpufail;
920    }
921
922    frontswap_register_ops(&zswap_frontswap_ops);
923    if (zswap_debugfs_init())
924        pr_warn("debugfs initialization failed\n");
925    return 0;
926pcpufail:
927    zswap_comp_exit();
928compfail:
929    zswap_entry_cache_destory();
930cachefail:
931    zbud_destroy_pool(zswap_pool);
932error:
933    return -ENOMEM;
934}
935/* must be late so crypto has time to come up */
936late_initcall(init_zswap);
937
938MODULE_LICENSE("GPL");
939MODULE_AUTHOR("Seth Jennings <sjenning@linux.vnet.ibm.com>");
940MODULE_DESCRIPTION("Compressed cache for swap pages");
941

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