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TOMOYO Linux Cross Reference
Linux/mm/zswap.c

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  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/zpool.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 /* Total bytes used by the compressed storage */
 49 static u64 zswap_pool_total_size;
 50 /* The number of compressed pages currently stored in zswap */
 51 static 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) */
 61 static u64 zswap_pool_limit_hit;
 62 /* Pages written back when pool limit was reached */
 63 static u64 zswap_written_back_pages;
 64 /* Store failed due to a reclaim failure after pool limit was reached */
 65 static u64 zswap_reject_reclaim_fail;
 66 /* Compressed page was too big for the allocator to (optimally) store */
 67 static u64 zswap_reject_compress_poor;
 68 /* Store failed because underlying allocator could not get memory */
 69 static u64 zswap_reject_alloc_fail;
 70 /* Store failed because the entry metadata could not be allocated (rare) */
 71 static u64 zswap_reject_kmemcache_fail;
 72 /* Duplicate store was encountered (rare) */
 73 static u64 zswap_duplicate_entry;
 74 
 75 /*********************************
 76 * tunables
 77 **********************************/
 78 /* Enable/disable zswap (disabled by default, fixed at boot for now) */
 79 static bool zswap_enabled __read_mostly;
 80 module_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"
 84 static char *zswap_compressor = ZSWAP_COMPRESSOR_DEFAULT;
 85 module_param_named(compressor, zswap_compressor, charp, 0444);
 86 
 87 /* The maximum percentage of memory that the compressed pool can occupy */
 88 static unsigned int zswap_max_pool_percent = 20;
 89 module_param_named(max_pool_percent,
 90                         zswap_max_pool_percent, uint, 0644);
 91 
 92 /* Compressed storage to use */
 93 #define ZSWAP_ZPOOL_DEFAULT "zbud"
 94 static char *zswap_zpool_type = ZSWAP_ZPOOL_DEFAULT;
 95 module_param_named(zpool, zswap_zpool_type, charp, 0444);
 96 
 97 /* zpool is shared by all of zswap backend  */
 98 static struct zpool *zswap_pool;
 99 
100 /*********************************
101 * compression functions
102 **********************************/
103 /* per-cpu compression transforms */
104 static struct crypto_comp * __percpu *zswap_comp_pcpu_tfms;
105 
106 enum comp_op {
107         ZSWAP_COMPOP_COMPRESS,
108         ZSWAP_COMPOP_DECOMPRESS
109 };
110 
111 static int zswap_comp_op(enum comp_op op, const u8 *src, unsigned int slen,
112                                 u8 *dst, unsigned int *dlen)
113 {
114         struct crypto_comp *tfm;
115         int ret;
116 
117         tfm = *per_cpu_ptr(zswap_comp_pcpu_tfms, get_cpu());
118         switch (op) {
119         case ZSWAP_COMPOP_COMPRESS:
120                 ret = crypto_comp_compress(tfm, src, slen, dst, dlen);
121                 break;
122         case ZSWAP_COMPOP_DECOMPRESS:
123                 ret = crypto_comp_decompress(tfm, src, slen, dst, dlen);
124                 break;
125         default:
126                 ret = -EINVAL;
127         }
128 
129         put_cpu();
130         return ret;
131 }
132 
133 static int __init zswap_comp_init(void)
134 {
135         if (!crypto_has_comp(zswap_compressor, 0, 0)) {
136                 pr_info("%s compressor not available\n", zswap_compressor);
137                 /* fall back to default compressor */
138                 zswap_compressor = ZSWAP_COMPRESSOR_DEFAULT;
139                 if (!crypto_has_comp(zswap_compressor, 0, 0))
140                         /* can't even load the default compressor */
141                         return -ENODEV;
142         }
143         pr_info("using %s compressor\n", zswap_compressor);
144 
145         /* alloc percpu transforms */
146         zswap_comp_pcpu_tfms = alloc_percpu(struct crypto_comp *);
147         if (!zswap_comp_pcpu_tfms)
148                 return -ENOMEM;
149         return 0;
150 }
151 
152 static void zswap_comp_exit(void)
153 {
154         /* free percpu transforms */
155         if (zswap_comp_pcpu_tfms)
156                 free_percpu(zswap_comp_pcpu_tfms);
157 }
158 
159 /*********************************
160 * data structures
161 **********************************/
162 /*
163  * struct zswap_entry
164  *
165  * This structure contains the metadata for tracking a single compressed
166  * page within zswap.
167  *
168  * rbnode - links the entry into red-black tree for the appropriate swap type
169  * refcount - the number of outstanding reference to the entry. This is needed
170  *            to protect against premature freeing of the entry by code
171  *            concurrent calls to load, invalidate, and writeback.  The lock
172  *            for the zswap_tree structure that contains the entry must
173  *            be held while changing the refcount.  Since the lock must
174  *            be held, there is no reason to also make refcount atomic.
175  * offset - the swap offset for the entry.  Index into the red-black tree.
176  * handle - zpool allocation handle that stores the compressed page data
177  * length - the length in bytes of the compressed page data.  Needed during
178  *          decompression
179  */
180 struct zswap_entry {
181         struct rb_node rbnode;
182         pgoff_t offset;
183         int refcount;
184         unsigned int length;
185         unsigned long handle;
186 };
187 
188 struct zswap_header {
189         swp_entry_t swpentry;
190 };
191 
192 /*
193  * The tree lock in the zswap_tree struct protects a few things:
194  * - the rbtree
195  * - the refcount field of each entry in the tree
196  */
197 struct zswap_tree {
198         struct rb_root rbroot;
199         spinlock_t lock;
200 };
201 
202 static struct zswap_tree *zswap_trees[MAX_SWAPFILES];
203 
204 /*********************************
205 * zswap entry functions
206 **********************************/
207 static struct kmem_cache *zswap_entry_cache;
208 
209 static int zswap_entry_cache_create(void)
210 {
211         zswap_entry_cache = KMEM_CACHE(zswap_entry, 0);
212         return zswap_entry_cache == NULL;
213 }
214 
215 static void __init zswap_entry_cache_destroy(void)
216 {
217         kmem_cache_destroy(zswap_entry_cache);
218 }
219 
220 static struct zswap_entry *zswap_entry_cache_alloc(gfp_t gfp)
221 {
222         struct zswap_entry *entry;
223         entry = kmem_cache_alloc(zswap_entry_cache, gfp);
224         if (!entry)
225                 return NULL;
226         entry->refcount = 1;
227         RB_CLEAR_NODE(&entry->rbnode);
228         return entry;
229 }
230 
231 static void zswap_entry_cache_free(struct zswap_entry *entry)
232 {
233         kmem_cache_free(zswap_entry_cache, entry);
234 }
235 
236 /*********************************
237 * rbtree functions
238 **********************************/
239 static struct zswap_entry *zswap_rb_search(struct rb_root *root, pgoff_t offset)
240 {
241         struct rb_node *node = root->rb_node;
242         struct zswap_entry *entry;
243 
244         while (node) {
245                 entry = rb_entry(node, struct zswap_entry, rbnode);
246                 if (entry->offset > offset)
247                         node = node->rb_left;
248                 else if (entry->offset < offset)
249                         node = node->rb_right;
250                 else
251                         return entry;
252         }
253         return NULL;
254 }
255 
256 /*
257  * In the case that a entry with the same offset is found, a pointer to
258  * the existing entry is stored in dupentry and the function returns -EEXIST
259  */
260 static int zswap_rb_insert(struct rb_root *root, struct zswap_entry *entry,
261                         struct zswap_entry **dupentry)
262 {
263         struct rb_node **link = &root->rb_node, *parent = NULL;
264         struct zswap_entry *myentry;
265 
266         while (*link) {
267                 parent = *link;
268                 myentry = rb_entry(parent, struct zswap_entry, rbnode);
269                 if (myentry->offset > entry->offset)
270                         link = &(*link)->rb_left;
271                 else if (myentry->offset < entry->offset)
272                         link = &(*link)->rb_right;
273                 else {
274                         *dupentry = myentry;
275                         return -EEXIST;
276                 }
277         }
278         rb_link_node(&entry->rbnode, parent, link);
279         rb_insert_color(&entry->rbnode, root);
280         return 0;
281 }
282 
283 static void zswap_rb_erase(struct rb_root *root, struct zswap_entry *entry)
284 {
285         if (!RB_EMPTY_NODE(&entry->rbnode)) {
286                 rb_erase(&entry->rbnode, root);
287                 RB_CLEAR_NODE(&entry->rbnode);
288         }
289 }
290 
291 /*
292  * Carries out the common pattern of freeing and entry's zpool allocation,
293  * freeing the entry itself, and decrementing the number of stored pages.
294  */
295 static void zswap_free_entry(struct zswap_entry *entry)
296 {
297         zpool_free(zswap_pool, entry->handle);
298         zswap_entry_cache_free(entry);
299         atomic_dec(&zswap_stored_pages);
300         zswap_pool_total_size = zpool_get_total_size(zswap_pool);
301 }
302 
303 /* caller must hold the tree lock */
304 static void zswap_entry_get(struct zswap_entry *entry)
305 {
306         entry->refcount++;
307 }
308 
309 /* caller must hold the tree lock
310 * remove from the tree and free it, if nobody reference the entry
311 */
312 static void zswap_entry_put(struct zswap_tree *tree,
313                         struct zswap_entry *entry)
314 {
315         int refcount = --entry->refcount;
316 
317         BUG_ON(refcount < 0);
318         if (refcount == 0) {
319                 zswap_rb_erase(&tree->rbroot, entry);
320                 zswap_free_entry(entry);
321         }
322 }
323 
324 /* caller must hold the tree lock */
325 static struct zswap_entry *zswap_entry_find_get(struct rb_root *root,
326                                 pgoff_t offset)
327 {
328         struct zswap_entry *entry = NULL;
329 
330         entry = zswap_rb_search(root, offset);
331         if (entry)
332                 zswap_entry_get(entry);
333 
334         return entry;
335 }
336 
337 /*********************************
338 * per-cpu code
339 **********************************/
340 static DEFINE_PER_CPU(u8 *, zswap_dstmem);
341 
342 static int __zswap_cpu_notifier(unsigned long action, unsigned long cpu)
343 {
344         struct crypto_comp *tfm;
345         u8 *dst;
346 
347         switch (action) {
348         case CPU_UP_PREPARE:
349                 tfm = crypto_alloc_comp(zswap_compressor, 0, 0);
350                 if (IS_ERR(tfm)) {
351                         pr_err("can't allocate compressor transform\n");
352                         return NOTIFY_BAD;
353                 }
354                 *per_cpu_ptr(zswap_comp_pcpu_tfms, cpu) = tfm;
355                 dst = kmalloc_node(PAGE_SIZE * 2, GFP_KERNEL, cpu_to_node(cpu));
356                 if (!dst) {
357                         pr_err("can't allocate compressor buffer\n");
358                         crypto_free_comp(tfm);
359                         *per_cpu_ptr(zswap_comp_pcpu_tfms, cpu) = NULL;
360                         return NOTIFY_BAD;
361                 }
362                 per_cpu(zswap_dstmem, cpu) = dst;
363                 break;
364         case CPU_DEAD:
365         case CPU_UP_CANCELED:
366                 tfm = *per_cpu_ptr(zswap_comp_pcpu_tfms, cpu);
367                 if (tfm) {
368                         crypto_free_comp(tfm);
369                         *per_cpu_ptr(zswap_comp_pcpu_tfms, cpu) = NULL;
370                 }
371                 dst = per_cpu(zswap_dstmem, cpu);
372                 kfree(dst);
373                 per_cpu(zswap_dstmem, cpu) = NULL;
374                 break;
375         default:
376                 break;
377         }
378         return NOTIFY_OK;
379 }
380 
381 static int zswap_cpu_notifier(struct notifier_block *nb,
382                                 unsigned long action, void *pcpu)
383 {
384         unsigned long cpu = (unsigned long)pcpu;
385         return __zswap_cpu_notifier(action, cpu);
386 }
387 
388 static struct notifier_block zswap_cpu_notifier_block = {
389         .notifier_call = zswap_cpu_notifier
390 };
391 
392 static int zswap_cpu_init(void)
393 {
394         unsigned long cpu;
395 
396         cpu_notifier_register_begin();
397         for_each_online_cpu(cpu)
398                 if (__zswap_cpu_notifier(CPU_UP_PREPARE, cpu) != NOTIFY_OK)
399                         goto cleanup;
400         __register_cpu_notifier(&zswap_cpu_notifier_block);
401         cpu_notifier_register_done();
402         return 0;
403 
404 cleanup:
405         for_each_online_cpu(cpu)
406                 __zswap_cpu_notifier(CPU_UP_CANCELED, cpu);
407         cpu_notifier_register_done();
408         return -ENOMEM;
409 }
410 
411 /*********************************
412 * helpers
413 **********************************/
414 static bool zswap_is_full(void)
415 {
416         return totalram_pages * zswap_max_pool_percent / 100 <
417                 DIV_ROUND_UP(zswap_pool_total_size, PAGE_SIZE);
418 }
419 
420 /*********************************
421 * writeback code
422 **********************************/
423 /* return enum for zswap_get_swap_cache_page */
424 enum zswap_get_swap_ret {
425         ZSWAP_SWAPCACHE_NEW,
426         ZSWAP_SWAPCACHE_EXIST,
427         ZSWAP_SWAPCACHE_FAIL,
428 };
429 
430 /*
431  * zswap_get_swap_cache_page
432  *
433  * This is an adaption of read_swap_cache_async()
434  *
435  * This function tries to find a page with the given swap entry
436  * in the swapper_space address space (the swap cache).  If the page
437  * is found, it is returned in retpage.  Otherwise, a page is allocated,
438  * added to the swap cache, and returned in retpage.
439  *
440  * If success, the swap cache page is returned in retpage
441  * Returns ZSWAP_SWAPCACHE_EXIST if page was already in the swap cache
442  * Returns ZSWAP_SWAPCACHE_NEW if the new page needs to be populated,
443  *     the new page is added to swapcache and locked
444  * Returns ZSWAP_SWAPCACHE_FAIL on error
445  */
446 static int zswap_get_swap_cache_page(swp_entry_t entry,
447                                 struct page **retpage)
448 {
449         struct page *found_page, *new_page = NULL;
450         struct address_space *swapper_space = swap_address_space(entry);
451         int err;
452 
453         *retpage = NULL;
454         do {
455                 /*
456                  * First check the swap cache.  Since this is normally
457                  * called after lookup_swap_cache() failed, re-calling
458                  * that would confuse statistics.
459                  */
460                 found_page = find_get_page(swapper_space, entry.val);
461                 if (found_page)
462                         break;
463 
464                 /*
465                  * Get a new page to read into from swap.
466                  */
467                 if (!new_page) {
468                         new_page = alloc_page(GFP_KERNEL);
469                         if (!new_page)
470                                 break; /* Out of memory */
471                 }
472 
473                 /*
474                  * call radix_tree_preload() while we can wait.
475                  */
476                 err = radix_tree_preload(GFP_KERNEL);
477                 if (err)
478                         break;
479 
480                 /*
481                  * Swap entry may have been freed since our caller observed it.
482                  */
483                 err = swapcache_prepare(entry);
484                 if (err == -EEXIST) { /* seems racy */
485                         radix_tree_preload_end();
486                         continue;
487                 }
488                 if (err) { /* swp entry is obsolete ? */
489                         radix_tree_preload_end();
490                         break;
491                 }
492 
493                 /* May fail (-ENOMEM) if radix-tree node allocation failed. */
494                 __set_page_locked(new_page);
495                 SetPageSwapBacked(new_page);
496                 err = __add_to_swap_cache(new_page, entry);
497                 if (likely(!err)) {
498                         radix_tree_preload_end();
499                         lru_cache_add_anon(new_page);
500                         *retpage = new_page;
501                         return ZSWAP_SWAPCACHE_NEW;
502                 }
503                 radix_tree_preload_end();
504                 ClearPageSwapBacked(new_page);
505                 __clear_page_locked(new_page);
506                 /*
507                  * add_to_swap_cache() doesn't return -EEXIST, so we can safely
508                  * clear SWAP_HAS_CACHE flag.
509                  */
510                 swapcache_free(entry);
511         } while (err != -ENOMEM);
512 
513         if (new_page)
514                 page_cache_release(new_page);
515         if (!found_page)
516                 return ZSWAP_SWAPCACHE_FAIL;
517         *retpage = found_page;
518         return ZSWAP_SWAPCACHE_EXIST;
519 }
520 
521 /*
522  * Attempts to free an entry by adding a page to the swap cache,
523  * decompressing the entry data into the page, and issuing a
524  * bio write to write the page back to the swap device.
525  *
526  * This can be thought of as a "resumed writeback" of the page
527  * to the swap device.  We are basically resuming the same swap
528  * writeback path that was intercepted with the frontswap_store()
529  * in the first place.  After the page has been decompressed into
530  * the swap cache, the compressed version stored by zswap can be
531  * freed.
532  */
533 static int zswap_writeback_entry(struct zpool *pool, unsigned long handle)
534 {
535         struct zswap_header *zhdr;
536         swp_entry_t swpentry;
537         struct zswap_tree *tree;
538         pgoff_t offset;
539         struct zswap_entry *entry;
540         struct page *page;
541         u8 *src, *dst;
542         unsigned int dlen;
543         int ret;
544         struct writeback_control wbc = {
545                 .sync_mode = WB_SYNC_NONE,
546         };
547 
548         /* extract swpentry from data */
549         zhdr = zpool_map_handle(pool, handle, ZPOOL_MM_RO);
550         swpentry = zhdr->swpentry; /* here */
551         zpool_unmap_handle(pool, handle);
552         tree = zswap_trees[swp_type(swpentry)];
553         offset = swp_offset(swpentry);
554 
555         /* find and ref zswap entry */
556         spin_lock(&tree->lock);
557         entry = zswap_entry_find_get(&tree->rbroot, offset);
558         if (!entry) {
559                 /* entry was invalidated */
560                 spin_unlock(&tree->lock);
561                 return 0;
562         }
563         spin_unlock(&tree->lock);
564         BUG_ON(offset != entry->offset);
565 
566         /* try to allocate swap cache page */
567         switch (zswap_get_swap_cache_page(swpentry, &page)) {
568         case ZSWAP_SWAPCACHE_FAIL: /* no memory or invalidate happened */
569                 ret = -ENOMEM;
570                 goto fail;
571 
572         case ZSWAP_SWAPCACHE_EXIST:
573                 /* page is already in the swap cache, ignore for now */
574                 page_cache_release(page);
575                 ret = -EEXIST;
576                 goto fail;
577 
578         case ZSWAP_SWAPCACHE_NEW: /* page is locked */
579                 /* decompress */
580                 dlen = PAGE_SIZE;
581                 src = (u8 *)zpool_map_handle(zswap_pool, entry->handle,
582                                 ZPOOL_MM_RO) + sizeof(struct zswap_header);
583                 dst = kmap_atomic(page);
584                 ret = zswap_comp_op(ZSWAP_COMPOP_DECOMPRESS, src,
585                                 entry->length, dst, &dlen);
586                 kunmap_atomic(dst);
587                 zpool_unmap_handle(zswap_pool, entry->handle);
588                 BUG_ON(ret);
589                 BUG_ON(dlen != PAGE_SIZE);
590 
591                 /* page is up to date */
592                 SetPageUptodate(page);
593         }
594 
595         /* move it to the tail of the inactive list after end_writeback */
596         SetPageReclaim(page);
597 
598         /* start writeback */
599         __swap_writepage(page, &wbc, end_swap_bio_write);
600         page_cache_release(page);
601         zswap_written_back_pages++;
602 
603         spin_lock(&tree->lock);
604         /* drop local reference */
605         zswap_entry_put(tree, entry);
606 
607         /*
608         * There are two possible situations for entry here:
609         * (1) refcount is 1(normal case),  entry is valid and on the tree
610         * (2) refcount is 0, entry is freed and not on the tree
611         *     because invalidate happened during writeback
612         *  search the tree and free the entry if find entry
613         */
614         if (entry == zswap_rb_search(&tree->rbroot, offset))
615                 zswap_entry_put(tree, entry);
616         spin_unlock(&tree->lock);
617 
618         goto end;
619 
620         /*
621         * if we get here due to ZSWAP_SWAPCACHE_EXIST
622         * a load may happening concurrently
623         * it is safe and okay to not free the entry
624         * if we free the entry in the following put
625         * it it either okay to return !0
626         */
627 fail:
628         spin_lock(&tree->lock);
629         zswap_entry_put(tree, entry);
630         spin_unlock(&tree->lock);
631 
632 end:
633         return ret;
634 }
635 
636 /*********************************
637 * frontswap hooks
638 **********************************/
639 /* attempts to compress and store an single page */
640 static int zswap_frontswap_store(unsigned type, pgoff_t offset,
641                                 struct page *page)
642 {
643         struct zswap_tree *tree = zswap_trees[type];
644         struct zswap_entry *entry, *dupentry;
645         int ret;
646         unsigned int dlen = PAGE_SIZE, len;
647         unsigned long handle;
648         char *buf;
649         u8 *src, *dst;
650         struct zswap_header *zhdr;
651 
652         if (!tree) {
653                 ret = -ENODEV;
654                 goto reject;
655         }
656 
657         /* reclaim space if needed */
658         if (zswap_is_full()) {
659                 zswap_pool_limit_hit++;
660                 if (zpool_shrink(zswap_pool, 1, NULL)) {
661                         zswap_reject_reclaim_fail++;
662                         ret = -ENOMEM;
663                         goto reject;
664                 }
665 
666                 /* A second zswap_is_full() check after
667                  * zswap_shrink() to make sure it's now
668                  * under the max_pool_percent
669                  */
670                 if (zswap_is_full()) {
671                         ret = -ENOMEM;
672                         goto reject;
673                 }
674         }
675 
676         /* allocate entry */
677         entry = zswap_entry_cache_alloc(GFP_KERNEL);
678         if (!entry) {
679                 zswap_reject_kmemcache_fail++;
680                 ret = -ENOMEM;
681                 goto reject;
682         }
683 
684         /* compress */
685         dst = get_cpu_var(zswap_dstmem);
686         src = kmap_atomic(page);
687         ret = zswap_comp_op(ZSWAP_COMPOP_COMPRESS, src, PAGE_SIZE, dst, &dlen);
688         kunmap_atomic(src);
689         if (ret) {
690                 ret = -EINVAL;
691                 goto freepage;
692         }
693 
694         /* store */
695         len = dlen + sizeof(struct zswap_header);
696         ret = zpool_malloc(zswap_pool, len, __GFP_NORETRY | __GFP_NOWARN,
697                 &handle);
698         if (ret == -ENOSPC) {
699                 zswap_reject_compress_poor++;
700                 goto freepage;
701         }
702         if (ret) {
703                 zswap_reject_alloc_fail++;
704                 goto freepage;
705         }
706         zhdr = zpool_map_handle(zswap_pool, handle, ZPOOL_MM_RW);
707         zhdr->swpentry = swp_entry(type, offset);
708         buf = (u8 *)(zhdr + 1);
709         memcpy(buf, dst, dlen);
710         zpool_unmap_handle(zswap_pool, handle);
711         put_cpu_var(zswap_dstmem);
712 
713         /* populate entry */
714         entry->offset = offset;
715         entry->handle = handle;
716         entry->length = dlen;
717 
718         /* map */
719         spin_lock(&tree->lock);
720         do {
721                 ret = zswap_rb_insert(&tree->rbroot, entry, &dupentry);
722                 if (ret == -EEXIST) {
723                         zswap_duplicate_entry++;
724                         /* remove from rbtree */
725                         zswap_rb_erase(&tree->rbroot, dupentry);
726                         zswap_entry_put(tree, dupentry);
727                 }
728         } while (ret == -EEXIST);
729         spin_unlock(&tree->lock);
730 
731         /* update stats */
732         atomic_inc(&zswap_stored_pages);
733         zswap_pool_total_size = zpool_get_total_size(zswap_pool);
734 
735         return 0;
736 
737 freepage:
738         put_cpu_var(zswap_dstmem);
739         zswap_entry_cache_free(entry);
740 reject:
741         return ret;
742 }
743 
744 /*
745  * returns 0 if the page was successfully decompressed
746  * return -1 on entry not found or error
747 */
748 static int zswap_frontswap_load(unsigned type, pgoff_t offset,
749                                 struct page *page)
750 {
751         struct zswap_tree *tree = zswap_trees[type];
752         struct zswap_entry *entry;
753         u8 *src, *dst;
754         unsigned int dlen;
755         int ret;
756 
757         /* find */
758         spin_lock(&tree->lock);
759         entry = zswap_entry_find_get(&tree->rbroot, offset);
760         if (!entry) {
761                 /* entry was written back */
762                 spin_unlock(&tree->lock);
763                 return -1;
764         }
765         spin_unlock(&tree->lock);
766 
767         /* decompress */
768         dlen = PAGE_SIZE;
769         src = (u8 *)zpool_map_handle(zswap_pool, entry->handle,
770                         ZPOOL_MM_RO) + sizeof(struct zswap_header);
771         dst = kmap_atomic(page);
772         ret = zswap_comp_op(ZSWAP_COMPOP_DECOMPRESS, src, entry->length,
773                 dst, &dlen);
774         kunmap_atomic(dst);
775         zpool_unmap_handle(zswap_pool, entry->handle);
776         BUG_ON(ret);
777 
778         spin_lock(&tree->lock);
779         zswap_entry_put(tree, entry);
780         spin_unlock(&tree->lock);
781 
782         return 0;
783 }
784 
785 /* frees an entry in zswap */
786 static void zswap_frontswap_invalidate_page(unsigned type, pgoff_t offset)
787 {
788         struct zswap_tree *tree = zswap_trees[type];
789         struct zswap_entry *entry;
790 
791         /* find */
792         spin_lock(&tree->lock);
793         entry = zswap_rb_search(&tree->rbroot, offset);
794         if (!entry) {
795                 /* entry was written back */
796                 spin_unlock(&tree->lock);
797                 return;
798         }
799 
800         /* remove from rbtree */
801         zswap_rb_erase(&tree->rbroot, entry);
802 
803         /* drop the initial reference from entry creation */
804         zswap_entry_put(tree, entry);
805 
806         spin_unlock(&tree->lock);
807 }
808 
809 /* frees all zswap entries for the given swap type */
810 static void zswap_frontswap_invalidate_area(unsigned type)
811 {
812         struct zswap_tree *tree = zswap_trees[type];
813         struct zswap_entry *entry, *n;
814 
815         if (!tree)
816                 return;
817 
818         /* walk the tree and free everything */
819         spin_lock(&tree->lock);
820         rbtree_postorder_for_each_entry_safe(entry, n, &tree->rbroot, rbnode)
821                 zswap_free_entry(entry);
822         tree->rbroot = RB_ROOT;
823         spin_unlock(&tree->lock);
824         kfree(tree);
825         zswap_trees[type] = NULL;
826 }
827 
828 static struct zpool_ops zswap_zpool_ops = {
829         .evict = zswap_writeback_entry
830 };
831 
832 static void zswap_frontswap_init(unsigned type)
833 {
834         struct zswap_tree *tree;
835 
836         tree = kzalloc(sizeof(struct zswap_tree), GFP_KERNEL);
837         if (!tree) {
838                 pr_err("alloc failed, zswap disabled for swap type %d\n", type);
839                 return;
840         }
841 
842         tree->rbroot = RB_ROOT;
843         spin_lock_init(&tree->lock);
844         zswap_trees[type] = tree;
845 }
846 
847 static struct frontswap_ops zswap_frontswap_ops = {
848         .store = zswap_frontswap_store,
849         .load = zswap_frontswap_load,
850         .invalidate_page = zswap_frontswap_invalidate_page,
851         .invalidate_area = zswap_frontswap_invalidate_area,
852         .init = zswap_frontswap_init
853 };
854 
855 /*********************************
856 * debugfs functions
857 **********************************/
858 #ifdef CONFIG_DEBUG_FS
859 #include <linux/debugfs.h>
860 
861 static struct dentry *zswap_debugfs_root;
862 
863 static int __init zswap_debugfs_init(void)
864 {
865         if (!debugfs_initialized())
866                 return -ENODEV;
867 
868         zswap_debugfs_root = debugfs_create_dir("zswap", NULL);
869         if (!zswap_debugfs_root)
870                 return -ENOMEM;
871 
872         debugfs_create_u64("pool_limit_hit", S_IRUGO,
873                         zswap_debugfs_root, &zswap_pool_limit_hit);
874         debugfs_create_u64("reject_reclaim_fail", S_IRUGO,
875                         zswap_debugfs_root, &zswap_reject_reclaim_fail);
876         debugfs_create_u64("reject_alloc_fail", S_IRUGO,
877                         zswap_debugfs_root, &zswap_reject_alloc_fail);
878         debugfs_create_u64("reject_kmemcache_fail", S_IRUGO,
879                         zswap_debugfs_root, &zswap_reject_kmemcache_fail);
880         debugfs_create_u64("reject_compress_poor", S_IRUGO,
881                         zswap_debugfs_root, &zswap_reject_compress_poor);
882         debugfs_create_u64("written_back_pages", S_IRUGO,
883                         zswap_debugfs_root, &zswap_written_back_pages);
884         debugfs_create_u64("duplicate_entry", S_IRUGO,
885                         zswap_debugfs_root, &zswap_duplicate_entry);
886         debugfs_create_u64("pool_total_size", S_IRUGO,
887                         zswap_debugfs_root, &zswap_pool_total_size);
888         debugfs_create_atomic_t("stored_pages", S_IRUGO,
889                         zswap_debugfs_root, &zswap_stored_pages);
890 
891         return 0;
892 }
893 
894 static void __exit zswap_debugfs_exit(void)
895 {
896         debugfs_remove_recursive(zswap_debugfs_root);
897 }
898 #else
899 static int __init zswap_debugfs_init(void)
900 {
901         return 0;
902 }
903 
904 static void __exit zswap_debugfs_exit(void) { }
905 #endif
906 
907 /*********************************
908 * module init and exit
909 **********************************/
910 static int __init init_zswap(void)
911 {
912         gfp_t gfp = __GFP_NORETRY | __GFP_NOWARN;
913 
914         if (!zswap_enabled)
915                 return 0;
916 
917         pr_info("loading zswap\n");
918 
919         zswap_pool = zpool_create_pool(zswap_zpool_type, gfp, &zswap_zpool_ops);
920         if (!zswap_pool && strcmp(zswap_zpool_type, ZSWAP_ZPOOL_DEFAULT)) {
921                 pr_info("%s zpool not available\n", zswap_zpool_type);
922                 zswap_zpool_type = ZSWAP_ZPOOL_DEFAULT;
923                 zswap_pool = zpool_create_pool(zswap_zpool_type, gfp,
924                                         &zswap_zpool_ops);
925         }
926         if (!zswap_pool) {
927                 pr_err("%s zpool not available\n", zswap_zpool_type);
928                 pr_err("zpool creation failed\n");
929                 goto error;
930         }
931         pr_info("using %s pool\n", zswap_zpool_type);
932 
933         if (zswap_entry_cache_create()) {
934                 pr_err("entry cache creation failed\n");
935                 goto cachefail;
936         }
937         if (zswap_comp_init()) {
938                 pr_err("compressor initialization failed\n");
939                 goto compfail;
940         }
941         if (zswap_cpu_init()) {
942                 pr_err("per-cpu initialization failed\n");
943                 goto pcpufail;
944         }
945 
946         frontswap_register_ops(&zswap_frontswap_ops);
947         if (zswap_debugfs_init())
948                 pr_warn("debugfs initialization failed\n");
949         return 0;
950 pcpufail:
951         zswap_comp_exit();
952 compfail:
953         zswap_entry_cache_destroy();
954 cachefail:
955         zpool_destroy_pool(zswap_pool);
956 error:
957         return -ENOMEM;
958 }
959 /* must be late so crypto has time to come up */
960 late_initcall(init_zswap);
961 
962 MODULE_LICENSE("GPL");
963 MODULE_AUTHOR("Seth Jennings <sjenning@linux.vnet.ibm.com>");
964 MODULE_DESCRIPTION("Compressed cache for swap pages");
965 

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