1// SPDX-License-Identifier: GPL-2.0-or-later
   2/*
   3 * zswap.c - zswap driver file
   4 *
   5 * zswap is a cache that takes pages that are in the process
   6 * of being swapped out and attempts to compress and store them in a
   7 * RAM-based memory pool.  This can result in a significant I/O reduction on
   8 * the swap device and, in the case where decompressing from RAM is faster
   9 * than reading from the swap device, can also improve workload performance.
  10 *
  11 * Copyright (C) 2012  Seth Jennings <sjenning@linux.vnet.ibm.com>
  12*/
  13
  14#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
  15
  16#include <linux/module.h>
  17#include <linux/cpu.h>
  18#include <linux/highmem.h>
  19#include <linux/slab.h>
  20#include <linux/spinlock.h>
  21#include <linux/types.h>
  22#include <linux/atomic.h>
 
 
  23#include <linux/swap.h>
  24#include <linux/crypto.h>
  25#include <linux/scatterlist.h>
  26#include <linux/mempolicy.h>
  27#include <linux/mempool.h>
  28#include <linux/zpool.h>
  29#include <crypto/acompress.h>
  30#include <linux/zswap.h>
  31#include <linux/mm_types.h>
  32#include <linux/page-flags.h>
  33#include <linux/swapops.h>
  34#include <linux/writeback.h>
  35#include <linux/pagemap.h>
  36#include <linux/workqueue.h>
  37#include <linux/list_lru.h>
  38
  39#include "swap.h"
  40#include "internal.h"
  41
  42/*********************************
  43* statistics
  44**********************************/
 
 
  45/* The number of compressed pages currently stored in zswap */
  46atomic_long_t zswap_stored_pages = ATOMIC_INIT(0);
 
 
  47
  48/*
  49 * The statistics below are not protected from concurrent access for
  50 * performance reasons so they may not be a 100% accurate.  However,
  51 * they do provide useful information on roughly how many times a
  52 * certain event is occurring.
  53*/
  54
  55/* Pool limit was hit (see zswap_max_pool_percent) */
  56static u64 zswap_pool_limit_hit;
  57/* Pages written back when pool limit was reached */
  58static u64 zswap_written_back_pages;
  59/* Store failed due to a reclaim failure after pool limit was reached */
  60static u64 zswap_reject_reclaim_fail;
  61/* Store failed due to compression algorithm failure */
  62static u64 zswap_reject_compress_fail;
  63/* Compressed page was too big for the allocator to (optimally) store */
  64static u64 zswap_reject_compress_poor;
  65/* Store failed because underlying allocator could not get memory */
  66static u64 zswap_reject_alloc_fail;
  67/* Store failed because the entry metadata could not be allocated (rare) */
  68static u64 zswap_reject_kmemcache_fail;
 
 
  69
  70/* Shrinker work queue */
  71static struct workqueue_struct *shrink_wq;
  72/* Pool limit was hit, we need to calm down */
  73static bool zswap_pool_reached_full;
  74
  75/*********************************
  76* tunables
  77**********************************/
  78
  79#define ZSWAP_PARAM_UNSET ""
  80
  81static int zswap_setup(void);
  82
  83/* Enable/disable zswap */
  84static DEFINE_STATIC_KEY_MAYBE(CONFIG_ZSWAP_DEFAULT_ON, zswap_ever_enabled);
  85static bool zswap_enabled = IS_ENABLED(CONFIG_ZSWAP_DEFAULT_ON);
  86static int zswap_enabled_param_set(const char *,
  87				   const struct kernel_param *);
  88static const struct kernel_param_ops zswap_enabled_param_ops = {
  89	.set =		zswap_enabled_param_set,
  90	.get =		param_get_bool,
  91};
  92module_param_cb(enabled, &zswap_enabled_param_ops, &zswap_enabled, 0644);
  93
  94/* Crypto compressor to use */
  95static char *zswap_compressor = CONFIG_ZSWAP_COMPRESSOR_DEFAULT;
  96static int zswap_compressor_param_set(const char *,
  97				      const struct kernel_param *);
  98static const struct kernel_param_ops zswap_compressor_param_ops = {
  99	.set =		zswap_compressor_param_set,
 100	.get =		param_get_charp,
 101	.free =		param_free_charp,
 102};
 103module_param_cb(compressor, &zswap_compressor_param_ops,
 104		&zswap_compressor, 0644);
 105
 106/* Compressed storage zpool to use */
 107static char *zswap_zpool_type = CONFIG_ZSWAP_ZPOOL_DEFAULT;
 108static int zswap_zpool_param_set(const char *, const struct kernel_param *);
 109static const struct kernel_param_ops zswap_zpool_param_ops = {
 110	.set =		zswap_zpool_param_set,
 111	.get =		param_get_charp,
 112	.free =		param_free_charp,
 113};
 114module_param_cb(zpool, &zswap_zpool_param_ops, &zswap_zpool_type, 0644);
 115
 116/* The maximum percentage of memory that the compressed pool can occupy */
 117static unsigned int zswap_max_pool_percent = 20;
 118module_param_named(max_pool_percent, zswap_max_pool_percent, uint, 0644);
 119
 120/* The threshold for accepting new pages after the max_pool_percent was hit */
 121static unsigned int zswap_accept_thr_percent = 90; /* of max pool size */
 122module_param_named(accept_threshold_percent, zswap_accept_thr_percent,
 123		   uint, 0644);
 124
 125/* Enable/disable memory pressure-based shrinker. */
 126static bool zswap_shrinker_enabled = IS_ENABLED(
 127		CONFIG_ZSWAP_SHRINKER_DEFAULT_ON);
 128module_param_named(shrinker_enabled, zswap_shrinker_enabled, bool, 0644);
 129
 130bool zswap_is_enabled(void)
 131{
 132	return zswap_enabled;
 133}
 134
 135bool zswap_never_enabled(void)
 136{
 137	return !static_branch_maybe(CONFIG_ZSWAP_DEFAULT_ON, &zswap_ever_enabled);
 138}
 139
 140/*********************************
 141* data structures
 142**********************************/
 143
 144struct crypto_acomp_ctx {
 145	struct crypto_acomp *acomp;
 146	struct acomp_req *req;
 147	struct crypto_wait wait;
 148	u8 *buffer;
 149	struct mutex mutex;
 150	bool is_sleepable;
 151};
 152
 153/*
 154 * The lock ordering is zswap_tree.lock -> zswap_pool.lru_lock.
 155 * The only case where lru_lock is not acquired while holding tree.lock is
 156 * when a zswap_entry is taken off the lru for writeback, in that case it
 157 * needs to be verified that it's still valid in the tree.
 158 */
 159struct zswap_pool {
 160	struct zpool *zpool;
 161	struct crypto_acomp_ctx __percpu *acomp_ctx;
 162	struct percpu_ref ref;
 163	struct list_head list;
 164	struct work_struct release_work;
 
 165	struct hlist_node node;
 166	char tfm_name[CRYPTO_MAX_ALG_NAME];
 167};
 168
 169/* Global LRU lists shared by all zswap pools. */
 170static struct list_lru zswap_list_lru;
 171
 172/* The lock protects zswap_next_shrink updates. */
 173static DEFINE_SPINLOCK(zswap_shrink_lock);
 174static struct mem_cgroup *zswap_next_shrink;
 175static struct work_struct zswap_shrink_work;
 176static struct shrinker *zswap_shrinker;
 177
 178/*
 179 * struct zswap_entry
 180 *
 181 * This structure contains the metadata for tracking a single compressed
 182 * page within zswap.
 183 *
 184 * swpentry - associated swap entry, the offset indexes into the red-black tree
 
 
 
 
 
 
 
 185 * length - the length in bytes of the compressed page data.  Needed during
 186 *          decompression.
 187 * referenced - true if the entry recently entered the zswap pool. Unset by the
 188 *              writeback logic. The entry is only reclaimed by the writeback
 189 *              logic if referenced is unset. See comments in the shrinker
 190 *              section for context.
 191 * pool - the zswap_pool the entry's data is in
 192 * handle - zpool allocation handle that stores the compressed page data
 193 * objcg - the obj_cgroup that the compressed memory is charged to
 194 * lru - handle to the pool's lru used to evict pages.
 195 */
 196struct zswap_entry {
 197	swp_entry_t swpentry;
 
 
 198	unsigned int length;
 199	bool referenced;
 200	struct zswap_pool *pool;
 201	unsigned long handle;
 202	struct obj_cgroup *objcg;
 203	struct list_head lru;
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 204};
 205
 206static struct xarray *zswap_trees[MAX_SWAPFILES];
 207static unsigned int nr_zswap_trees[MAX_SWAPFILES];
 208
 209/* RCU-protected iteration */
 210static LIST_HEAD(zswap_pools);
 211/* protects zswap_pools list modification */
 212static DEFINE_SPINLOCK(zswap_pools_lock);
 213/* pool counter to provide unique names to zpool */
 214static atomic_t zswap_pools_count = ATOMIC_INIT(0);
 215
 216enum zswap_init_type {
 217	ZSWAP_UNINIT,
 218	ZSWAP_INIT_SUCCEED,
 219	ZSWAP_INIT_FAILED
 220};
 221
 222static enum zswap_init_type zswap_init_state;
 223
 224/* used to ensure the integrity of initialization */
 225static DEFINE_MUTEX(zswap_init_lock);
 226
 227/* init completed, but couldn't create the initial pool */
 228static bool zswap_has_pool;
 229
 230/*********************************
 231* helpers and fwd declarations
 232**********************************/
 233
 234static inline struct xarray *swap_zswap_tree(swp_entry_t swp)
 235{
 236	return &zswap_trees[swp_type(swp)][swp_offset(swp)
 237		>> SWAP_ADDRESS_SPACE_SHIFT];
 238}
 239
 240#define zswap_pool_debug(msg, p)				\
 241	pr_debug("%s pool %s/%s\n", msg, (p)->tfm_name,		\
 242		 zpool_get_type((p)->zpool))
 243
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 244/*********************************
 245* pool functions
 246**********************************/
 247static void __zswap_pool_empty(struct percpu_ref *ref);
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 248
 249static struct zswap_pool *zswap_pool_create(char *type, char *compressor)
 250{
 251	struct zswap_pool *pool;
 252	char name[38]; /* 'zswap' + 32 char (max) num + \0 */
 253	gfp_t gfp = __GFP_NORETRY | __GFP_NOWARN | __GFP_KSWAPD_RECLAIM;
 254	int ret, cpu;
 255
 256	if (!zswap_has_pool) {
 257		/* if either are unset, pool initialization failed, and we
 258		 * need both params to be set correctly before trying to
 259		 * create a pool.
 260		 */
 261		if (!strcmp(type, ZSWAP_PARAM_UNSET))
 262			return NULL;
 263		if (!strcmp(compressor, ZSWAP_PARAM_UNSET))
 264			return NULL;
 265	}
 266
 267	pool = kzalloc(sizeof(*pool), GFP_KERNEL);
 268	if (!pool)
 269		return NULL;
 270
 271	/* unique name for each pool specifically required by zsmalloc */
 272	snprintf(name, 38, "zswap%x", atomic_inc_return(&zswap_pools_count));
 273	pool->zpool = zpool_create_pool(type, name, gfp);
 
 274	if (!pool->zpool) {
 275		pr_err("%s zpool not available\n", type);
 276		goto error;
 277	}
 278	pr_debug("using %s zpool\n", zpool_get_type(pool->zpool));
 279
 280	strscpy(pool->tfm_name, compressor, sizeof(pool->tfm_name));
 281
 282	pool->acomp_ctx = alloc_percpu(*pool->acomp_ctx);
 283	if (!pool->acomp_ctx) {
 284		pr_err("percpu alloc failed\n");
 285		goto error;
 286	}
 287
 288	for_each_possible_cpu(cpu)
 289		mutex_init(&per_cpu_ptr(pool->acomp_ctx, cpu)->mutex);
 290
 291	ret = cpuhp_state_add_instance(CPUHP_MM_ZSWP_POOL_PREPARE,
 292				       &pool->node);
 293	if (ret)
 294		goto error;
 
 295
 296	/* being the current pool takes 1 ref; this func expects the
 297	 * caller to always add the new pool as the current pool
 298	 */
 299	ret = percpu_ref_init(&pool->ref, __zswap_pool_empty,
 300			      PERCPU_REF_ALLOW_REINIT, GFP_KERNEL);
 301	if (ret)
 302		goto ref_fail;
 303	INIT_LIST_HEAD(&pool->list);
 
 304
 305	zswap_pool_debug("created", pool);
 306
 307	return pool;
 308
 309ref_fail:
 310	cpuhp_state_remove_instance(CPUHP_MM_ZSWP_POOL_PREPARE, &pool->node);
 311error:
 312	if (pool->acomp_ctx)
 313		free_percpu(pool->acomp_ctx);
 314	if (pool->zpool)
 315		zpool_destroy_pool(pool->zpool);
 316	kfree(pool);
 317	return NULL;
 318}
 319
 320static struct zswap_pool *__zswap_pool_create_fallback(void)
 321{
 322	bool has_comp, has_zpool;
 323
 324	has_comp = crypto_has_acomp(zswap_compressor, 0, 0);
 325	if (!has_comp && strcmp(zswap_compressor,
 326				CONFIG_ZSWAP_COMPRESSOR_DEFAULT)) {
 327		pr_err("compressor %s not available, using default %s\n",
 328		       zswap_compressor, CONFIG_ZSWAP_COMPRESSOR_DEFAULT);
 329		param_free_charp(&zswap_compressor);
 330		zswap_compressor = CONFIG_ZSWAP_COMPRESSOR_DEFAULT;
 331		has_comp = crypto_has_acomp(zswap_compressor, 0, 0);
 332	}
 333	if (!has_comp) {
 334		pr_err("default compressor %s not available\n",
 335		       zswap_compressor);
 336		param_free_charp(&zswap_compressor);
 337		zswap_compressor = ZSWAP_PARAM_UNSET;
 338	}
 339
 340	has_zpool = zpool_has_pool(zswap_zpool_type);
 341	if (!has_zpool && strcmp(zswap_zpool_type,
 342				 CONFIG_ZSWAP_ZPOOL_DEFAULT)) {
 343		pr_err("zpool %s not available, using default %s\n",
 344		       zswap_zpool_type, CONFIG_ZSWAP_ZPOOL_DEFAULT);
 345		param_free_charp(&zswap_zpool_type);
 346		zswap_zpool_type = CONFIG_ZSWAP_ZPOOL_DEFAULT;
 347		has_zpool = zpool_has_pool(zswap_zpool_type);
 348	}
 349	if (!has_zpool) {
 350		pr_err("default zpool %s not available\n",
 351		       zswap_zpool_type);
 352		param_free_charp(&zswap_zpool_type);
 353		zswap_zpool_type = ZSWAP_PARAM_UNSET;
 354	}
 355
 356	if (!has_comp || !has_zpool)
 357		return NULL;
 358
 359	return zswap_pool_create(zswap_zpool_type, zswap_compressor);
 360}
 361
 362static void zswap_pool_destroy(struct zswap_pool *pool)
 363{
 364	zswap_pool_debug("destroying", pool);
 365
 366	cpuhp_state_remove_instance(CPUHP_MM_ZSWP_POOL_PREPARE, &pool->node);
 367	free_percpu(pool->acomp_ctx);
 368
 369	zpool_destroy_pool(pool->zpool);
 370	kfree(pool);
 371}
 372
 
 
 
 
 
 
 
 
 373static void __zswap_pool_release(struct work_struct *work)
 374{
 375	struct zswap_pool *pool = container_of(work, typeof(*pool),
 376						release_work);
 377
 378	synchronize_rcu();
 379
 380	/* nobody should have been able to get a ref... */
 381	WARN_ON(!percpu_ref_is_zero(&pool->ref));
 382	percpu_ref_exit(&pool->ref);
 383
 384	/* pool is now off zswap_pools list and has no references. */
 385	zswap_pool_destroy(pool);
 386}
 387
 388static struct zswap_pool *zswap_pool_current(void);
 389
 390static void __zswap_pool_empty(struct percpu_ref *ref)
 391{
 392	struct zswap_pool *pool;
 393
 394	pool = container_of(ref, typeof(*pool), ref);
 395
 396	spin_lock_bh(&zswap_pools_lock);
 397
 398	WARN_ON(pool == zswap_pool_current());
 399
 400	list_del_rcu(&pool->list);
 401
 402	INIT_WORK(&pool->release_work, __zswap_pool_release);
 403	schedule_work(&pool->release_work);
 404
 405	spin_unlock_bh(&zswap_pools_lock);
 406}
 407
 408static int __must_check zswap_pool_tryget(struct zswap_pool *pool)
 409{
 410	if (!pool)
 411		return 0;
 412
 413	return percpu_ref_tryget(&pool->ref);
 414}
 415
 416/* The caller must already have a reference. */
 417static void zswap_pool_get(struct zswap_pool *pool)
 418{
 419	percpu_ref_get(&pool->ref);
 420}
 421
 422static void zswap_pool_put(struct zswap_pool *pool)
 423{
 424	percpu_ref_put(&pool->ref);
 425}
 426
 427static struct zswap_pool *__zswap_pool_current(void)
 428{
 429	struct zswap_pool *pool;
 430
 431	pool = list_first_or_null_rcu(&zswap_pools, typeof(*pool), list);
 432	WARN_ONCE(!pool && zswap_has_pool,
 433		  "%s: no page storage pool!\n", __func__);
 434
 435	return pool;
 436}
 437
 438static struct zswap_pool *zswap_pool_current(void)
 439{
 440	assert_spin_locked(&zswap_pools_lock);
 441
 442	return __zswap_pool_current();
 443}
 444
 445static struct zswap_pool *zswap_pool_current_get(void)
 446{
 447	struct zswap_pool *pool;
 448
 449	rcu_read_lock();
 450
 451	pool = __zswap_pool_current();
 452	if (!zswap_pool_tryget(pool))
 453		pool = NULL;
 454
 455	rcu_read_unlock();
 456
 457	return pool;
 458}
 459
 460/* type and compressor must be null-terminated */
 461static struct zswap_pool *zswap_pool_find_get(char *type, char *compressor)
 462{
 463	struct zswap_pool *pool;
 464
 465	assert_spin_locked(&zswap_pools_lock);
 466
 467	list_for_each_entry_rcu(pool, &zswap_pools, list) {
 468		if (strcmp(pool->tfm_name, compressor))
 469			continue;
 470		if (strcmp(zpool_get_type(pool->zpool), type))
 471			continue;
 472		/* if we can't get it, it's about to be destroyed */
 473		if (!zswap_pool_tryget(pool))
 474			continue;
 475		return pool;
 476	}
 477
 478	return NULL;
 479}
 480
 481static unsigned long zswap_max_pages(void)
 482{
 483	return totalram_pages() * zswap_max_pool_percent / 100;
 484}
 485
 486static unsigned long zswap_accept_thr_pages(void)
 487{
 488	return zswap_max_pages() * zswap_accept_thr_percent / 100;
 489}
 490
 491unsigned long zswap_total_pages(void)
 492{
 493	struct zswap_pool *pool;
 494	unsigned long total = 0;
 495
 496	rcu_read_lock();
 497	list_for_each_entry_rcu(pool, &zswap_pools, list)
 498		total += zpool_get_total_pages(pool->zpool);
 499	rcu_read_unlock();
 500
 501	return total;
 502}
 503
 504static bool zswap_check_limits(void)
 505{
 506	unsigned long cur_pages = zswap_total_pages();
 507	unsigned long max_pages = zswap_max_pages();
 508
 509	if (cur_pages >= max_pages) {
 510		zswap_pool_limit_hit++;
 511		zswap_pool_reached_full = true;
 512	} else if (zswap_pool_reached_full &&
 513		   cur_pages <= zswap_accept_thr_pages()) {
 514			zswap_pool_reached_full = false;
 515	}
 516	return zswap_pool_reached_full;
 517}
 518
 519/*********************************
 520* param callbacks
 521**********************************/
 522
 523static bool zswap_pool_changed(const char *s, const struct kernel_param *kp)
 524{
 525	/* no change required */
 526	if (!strcmp(s, *(char **)kp->arg) && zswap_has_pool)
 527		return false;
 528	return true;
 529}
 530
 531/* val must be a null-terminated string */
 532static int __zswap_param_set(const char *val, const struct kernel_param *kp,
 533			     char *type, char *compressor)
 534{
 535	struct zswap_pool *pool, *put_pool = NULL;
 536	char *s = strstrip((char *)val);
 537	int ret = 0;
 538	bool new_pool = false;
 539
 540	mutex_lock(&zswap_init_lock);
 541	switch (zswap_init_state) {
 542	case ZSWAP_UNINIT:
 543		/* if this is load-time (pre-init) param setting,
 544		 * don't create a pool; that's done during init.
 545		 */
 546		ret = param_set_charp(s, kp);
 547		break;
 548	case ZSWAP_INIT_SUCCEED:
 549		new_pool = zswap_pool_changed(s, kp);
 550		break;
 551	case ZSWAP_INIT_FAILED:
 552		pr_err("can't set param, initialization failed\n");
 553		ret = -ENODEV;
 554	}
 555	mutex_unlock(&zswap_init_lock);
 556
 557	/* no need to create a new pool, return directly */
 558	if (!new_pool)
 559		return ret;
 
 
 
 
 
 
 560
 561	if (!type) {
 562		if (!zpool_has_pool(s)) {
 563			pr_err("zpool %s not available\n", s);
 564			return -ENOENT;
 565		}
 566		type = s;
 567	} else if (!compressor) {
 568		if (!crypto_has_acomp(s, 0, 0)) {
 569			pr_err("compressor %s not available\n", s);
 570			return -ENOENT;
 571		}
 572		compressor = s;
 573	} else {
 574		WARN_ON(1);
 575		return -EINVAL;
 576	}
 577
 578	spin_lock_bh(&zswap_pools_lock);
 579
 580	pool = zswap_pool_find_get(type, compressor);
 581	if (pool) {
 582		zswap_pool_debug("using existing", pool);
 583		WARN_ON(pool == zswap_pool_current());
 584		list_del_rcu(&pool->list);
 585	}
 586
 587	spin_unlock_bh(&zswap_pools_lock);
 588
 589	if (!pool)
 590		pool = zswap_pool_create(type, compressor);
 591	else {
 592		/*
 593		 * Restore the initial ref dropped by percpu_ref_kill()
 594		 * when the pool was decommissioned and switch it again
 595		 * to percpu mode.
 596		 */
 597		percpu_ref_resurrect(&pool->ref);
 598
 599		/* Drop the ref from zswap_pool_find_get(). */
 600		zswap_pool_put(pool);
 601	}
 602
 603	if (pool)
 604		ret = param_set_charp(s, kp);
 605	else
 606		ret = -EINVAL;
 607
 608	spin_lock_bh(&zswap_pools_lock);
 609
 610	if (!ret) {
 611		put_pool = zswap_pool_current();
 612		list_add_rcu(&pool->list, &zswap_pools);
 613		zswap_has_pool = true;
 614	} else if (pool) {
 615		/* add the possibly pre-existing pool to the end of the pools
 616		 * list; if it's new (and empty) then it'll be removed and
 617		 * destroyed by the put after we drop the lock
 618		 */
 619		list_add_tail_rcu(&pool->list, &zswap_pools);
 620		put_pool = pool;
 621	}
 622
 623	spin_unlock_bh(&zswap_pools_lock);
 624
 625	if (!zswap_has_pool && !pool) {
 626		/* if initial pool creation failed, and this pool creation also
 627		 * failed, maybe both compressor and zpool params were bad.
 628		 * Allow changing this param, so pool creation will succeed
 629		 * when the other param is changed. We already verified this
 630		 * param is ok in the zpool_has_pool() or crypto_has_acomp()
 631		 * checks above.
 632		 */
 633		ret = param_set_charp(s, kp);
 634	}
 635
 636	/* drop the ref from either the old current pool,
 637	 * or the new pool we failed to add
 638	 */
 639	if (put_pool)
 640		percpu_ref_kill(&put_pool->ref);
 641
 642	return ret;
 643}
 644
 645static int zswap_compressor_param_set(const char *val,
 646				      const struct kernel_param *kp)
 647{
 648	return __zswap_param_set(val, kp, zswap_zpool_type, NULL);
 649}
 650
 651static int zswap_zpool_param_set(const char *val,
 652				 const struct kernel_param *kp)
 653{
 654	return __zswap_param_set(val, kp, NULL, zswap_compressor);
 655}
 656
 657static int zswap_enabled_param_set(const char *val,
 658				   const struct kernel_param *kp)
 659{
 660	int ret = -ENODEV;
 661
 662	/* if this is load-time (pre-init) param setting, only set param. */
 663	if (system_state != SYSTEM_RUNNING)
 664		return param_set_bool(val, kp);
 665
 666	mutex_lock(&zswap_init_lock);
 667	switch (zswap_init_state) {
 668	case ZSWAP_UNINIT:
 669		if (zswap_setup())
 670			break;
 671		fallthrough;
 672	case ZSWAP_INIT_SUCCEED:
 673		if (!zswap_has_pool)
 674			pr_err("can't enable, no pool configured\n");
 675		else
 676			ret = param_set_bool(val, kp);
 677		break;
 678	case ZSWAP_INIT_FAILED:
 679		pr_err("can't enable, initialization failed\n");
 
 
 
 
 
 680	}
 681	mutex_unlock(&zswap_init_lock);
 682
 683	return ret;
 684}
 685
 686/*********************************
 687* lru functions
 688**********************************/
 689
 690/* should be called under RCU */
 691#ifdef CONFIG_MEMCG
 692static inline struct mem_cgroup *mem_cgroup_from_entry(struct zswap_entry *entry)
 693{
 694	return entry->objcg ? obj_cgroup_memcg(entry->objcg) : NULL;
 695}
 696#else
 697static inline struct mem_cgroup *mem_cgroup_from_entry(struct zswap_entry *entry)
 698{
 699	return NULL;
 700}
 701#endif
 702
 703static inline int entry_to_nid(struct zswap_entry *entry)
 704{
 705	return page_to_nid(virt_to_page(entry));
 706}
 707
 708static void zswap_lru_add(struct list_lru *list_lru, struct zswap_entry *entry)
 709{
 710	int nid = entry_to_nid(entry);
 711	struct mem_cgroup *memcg;
 712
 713	/*
 714	 * Note that it is safe to use rcu_read_lock() here, even in the face of
 715	 * concurrent memcg offlining:
 716	 *
 717	 * 1. list_lru_add() is called before list_lru_one is dead. The
 718	 *    new entry will be reparented to memcg's parent's list_lru.
 719	 * 2. list_lru_add() is called after list_lru_one is dead. The
 720	 *    new entry will be added directly to memcg's parent's list_lru.
 721	 *
 722	 * Similar reasoning holds for list_lru_del().
 723	 */
 724	rcu_read_lock();
 725	memcg = mem_cgroup_from_entry(entry);
 726	/* will always succeed */
 727	list_lru_add(list_lru, &entry->lru, nid, memcg);
 728	rcu_read_unlock();
 729}
 730
 731static void zswap_lru_del(struct list_lru *list_lru, struct zswap_entry *entry)
 732{
 733	int nid = entry_to_nid(entry);
 734	struct mem_cgroup *memcg;
 735
 736	rcu_read_lock();
 737	memcg = mem_cgroup_from_entry(entry);
 738	/* will always succeed */
 739	list_lru_del(list_lru, &entry->lru, nid, memcg);
 740	rcu_read_unlock();
 741}
 742
 743void zswap_lruvec_state_init(struct lruvec *lruvec)
 744{
 745	atomic_long_set(&lruvec->zswap_lruvec_state.nr_disk_swapins, 0);
 746}
 747
 748void zswap_folio_swapin(struct folio *folio)
 749{
 750	struct lruvec *lruvec;
 751
 752	if (folio) {
 753		lruvec = folio_lruvec(folio);
 754		atomic_long_inc(&lruvec->zswap_lruvec_state.nr_disk_swapins);
 755	}
 756}
 757
 758/*
 759 * This function should be called when a memcg is being offlined.
 760 *
 761 * Since the global shrinker shrink_worker() may hold a reference
 762 * of the memcg, we must check and release the reference in
 763 * zswap_next_shrink.
 764 *
 765 * shrink_worker() must handle the case where this function releases
 766 * the reference of memcg being shrunk.
 767 */
 768void zswap_memcg_offline_cleanup(struct mem_cgroup *memcg)
 769{
 770	/* lock out zswap shrinker walking memcg tree */
 771	spin_lock(&zswap_shrink_lock);
 772	if (zswap_next_shrink == memcg) {
 773		do {
 774			zswap_next_shrink = mem_cgroup_iter(NULL, zswap_next_shrink, NULL);
 775		} while (zswap_next_shrink && !mem_cgroup_online(zswap_next_shrink));
 776	}
 777	spin_unlock(&zswap_shrink_lock);
 778}
 779
 780/*********************************
 781* zswap entry functions
 782**********************************/
 783static struct kmem_cache *zswap_entry_cache;
 784
 785static struct zswap_entry *zswap_entry_cache_alloc(gfp_t gfp, int nid)
 786{
 787	struct zswap_entry *entry;
 788	entry = kmem_cache_alloc_node(zswap_entry_cache, gfp, nid);
 789	if (!entry)
 790		return NULL;
 791	return entry;
 792}
 793
 794static void zswap_entry_cache_free(struct zswap_entry *entry)
 795{
 796	kmem_cache_free(zswap_entry_cache, entry);
 797}
 798
 799/*
 800 * Carries out the common pattern of freeing and entry's zpool allocation,
 801 * freeing the entry itself, and decrementing the number of stored pages.
 802 */
 803static void zswap_entry_free(struct zswap_entry *entry)
 804{
 805	zswap_lru_del(&zswap_list_lru, entry);
 806	zpool_free(entry->pool->zpool, entry->handle);
 807	zswap_pool_put(entry->pool);
 808	if (entry->objcg) {
 809		obj_cgroup_uncharge_zswap(entry->objcg, entry->length);
 810		obj_cgroup_put(entry->objcg);
 811	}
 812	zswap_entry_cache_free(entry);
 813	atomic_long_dec(&zswap_stored_pages);
 814}
 815
 816/*********************************
 817* compressed storage functions
 818**********************************/
 819static int zswap_cpu_comp_prepare(unsigned int cpu, struct hlist_node *node)
 820{
 821	struct zswap_pool *pool = hlist_entry(node, struct zswap_pool, node);
 822	struct crypto_acomp_ctx *acomp_ctx = per_cpu_ptr(pool->acomp_ctx, cpu);
 823	struct crypto_acomp *acomp = NULL;
 824	struct acomp_req *req = NULL;
 825	u8 *buffer = NULL;
 826	int ret;
 827
 828	buffer = kmalloc_node(PAGE_SIZE * 2, GFP_KERNEL, cpu_to_node(cpu));
 829	if (!buffer) {
 830		ret = -ENOMEM;
 831		goto fail;
 832	}
 833
 834	acomp = crypto_alloc_acomp_node(pool->tfm_name, 0, 0, cpu_to_node(cpu));
 835	if (IS_ERR(acomp)) {
 836		pr_err("could not alloc crypto acomp %s : %ld\n",
 837				pool->tfm_name, PTR_ERR(acomp));
 838		ret = PTR_ERR(acomp);
 839		goto fail;
 840	}
 841
 842	req = acomp_request_alloc(acomp);
 843	if (!req) {
 844		pr_err("could not alloc crypto acomp_request %s\n",
 845		       pool->tfm_name);
 846		ret = -ENOMEM;
 847		goto fail;
 848	}
 849
 850	/*
 851	 * Only hold the mutex after completing allocations, otherwise we may
 852	 * recurse into zswap through reclaim and attempt to hold the mutex
 853	 * again resulting in a deadlock.
 854	 */
 855	mutex_lock(&acomp_ctx->mutex);
 856	crypto_init_wait(&acomp_ctx->wait);
 857
 858	/*
 859	 * if the backend of acomp is async zip, crypto_req_done() will wakeup
 860	 * crypto_wait_req(); if the backend of acomp is scomp, the callback
 861	 * won't be called, crypto_wait_req() will return without blocking.
 862	 */
 863	acomp_request_set_callback(req, CRYPTO_TFM_REQ_MAY_BACKLOG,
 864				   crypto_req_done, &acomp_ctx->wait);
 865
 866	acomp_ctx->buffer = buffer;
 867	acomp_ctx->acomp = acomp;
 868	acomp_ctx->is_sleepable = acomp_is_async(acomp);
 869	acomp_ctx->req = req;
 870	mutex_unlock(&acomp_ctx->mutex);
 871	return 0;
 872
 873fail:
 874	if (acomp)
 875		crypto_free_acomp(acomp);
 876	kfree(buffer);
 877	return ret;
 878}
 879
 880static int zswap_cpu_comp_dead(unsigned int cpu, struct hlist_node *node)
 881{
 882	struct zswap_pool *pool = hlist_entry(node, struct zswap_pool, node);
 883	struct crypto_acomp_ctx *acomp_ctx = per_cpu_ptr(pool->acomp_ctx, cpu);
 884
 885	mutex_lock(&acomp_ctx->mutex);
 886	if (!IS_ERR_OR_NULL(acomp_ctx)) {
 887		if (!IS_ERR_OR_NULL(acomp_ctx->req))
 888			acomp_request_free(acomp_ctx->req);
 889		acomp_ctx->req = NULL;
 890		if (!IS_ERR_OR_NULL(acomp_ctx->acomp))
 891			crypto_free_acomp(acomp_ctx->acomp);
 892		kfree(acomp_ctx->buffer);
 893	}
 894	mutex_unlock(&acomp_ctx->mutex);
 895
 896	return 0;
 897}
 898
 899static struct crypto_acomp_ctx *acomp_ctx_get_cpu_lock(struct zswap_pool *pool)
 900{
 901	struct crypto_acomp_ctx *acomp_ctx;
 902
 903	for (;;) {
 904		acomp_ctx = raw_cpu_ptr(pool->acomp_ctx);
 905		mutex_lock(&acomp_ctx->mutex);
 906		if (likely(acomp_ctx->req))
 907			return acomp_ctx;
 908		/*
 909		 * It is possible that we were migrated to a different CPU after
 910		 * getting the per-CPU ctx but before the mutex was acquired. If
 911		 * the old CPU got offlined, zswap_cpu_comp_dead() could have
 912		 * already freed ctx->req (among other things) and set it to
 913		 * NULL. Just try again on the new CPU that we ended up on.
 914		 */
 915		mutex_unlock(&acomp_ctx->mutex);
 916	}
 917}
 918
 919static void acomp_ctx_put_unlock(struct crypto_acomp_ctx *acomp_ctx)
 920{
 921	mutex_unlock(&acomp_ctx->mutex);
 922}
 923
 924static bool zswap_compress(struct page *page, struct zswap_entry *entry,
 925			   struct zswap_pool *pool)
 926{
 927	struct crypto_acomp_ctx *acomp_ctx;
 928	struct scatterlist input, output;
 929	int comp_ret = 0, alloc_ret = 0;
 930	unsigned int dlen = PAGE_SIZE;
 931	unsigned long handle;
 932	struct zpool *zpool;
 933	char *buf;
 934	gfp_t gfp;
 935	u8 *dst;
 936
 937	acomp_ctx = acomp_ctx_get_cpu_lock(pool);
 938	dst = acomp_ctx->buffer;
 939	sg_init_table(&input, 1);
 940	sg_set_page(&input, page, PAGE_SIZE, 0);
 941
 942	/*
 943	 * We need PAGE_SIZE * 2 here since there maybe over-compression case,
 944	 * and hardware-accelerators may won't check the dst buffer size, so
 945	 * giving the dst buffer with enough length to avoid buffer overflow.
 946	 */
 947	sg_init_one(&output, dst, PAGE_SIZE * 2);
 948	acomp_request_set_params(acomp_ctx->req, &input, &output, PAGE_SIZE, dlen);
 949
 950	/*
 951	 * it maybe looks a little bit silly that we send an asynchronous request,
 952	 * then wait for its completion synchronously. This makes the process look
 953	 * synchronous in fact.
 954	 * Theoretically, acomp supports users send multiple acomp requests in one
 955	 * acomp instance, then get those requests done simultaneously. but in this
 956	 * case, zswap actually does store and load page by page, there is no
 957	 * existing method to send the second page before the first page is done
 958	 * in one thread doing zwap.
 959	 * but in different threads running on different cpu, we have different
 960	 * acomp instance, so multiple threads can do (de)compression in parallel.
 961	 */
 962	comp_ret = crypto_wait_req(crypto_acomp_compress(acomp_ctx->req), &acomp_ctx->wait);
 963	dlen = acomp_ctx->req->dlen;
 964	if (comp_ret)
 965		goto unlock;
 966
 967	zpool = pool->zpool;
 968	gfp = __GFP_NORETRY | __GFP_NOWARN | __GFP_KSWAPD_RECLAIM;
 969	if (zpool_malloc_support_movable(zpool))
 970		gfp |= __GFP_HIGHMEM | __GFP_MOVABLE;
 971	alloc_ret = zpool_malloc(zpool, dlen, gfp, &handle);
 972	if (alloc_ret)
 973		goto unlock;
 974
 975	buf = zpool_map_handle(zpool, handle, ZPOOL_MM_WO);
 976	memcpy(buf, dst, dlen);
 977	zpool_unmap_handle(zpool, handle);
 978
 979	entry->handle = handle;
 980	entry->length = dlen;
 981
 982unlock:
 983	if (comp_ret == -ENOSPC || alloc_ret == -ENOSPC)
 984		zswap_reject_compress_poor++;
 985	else if (comp_ret)
 986		zswap_reject_compress_fail++;
 987	else if (alloc_ret)
 988		zswap_reject_alloc_fail++;
 989
 990	acomp_ctx_put_unlock(acomp_ctx);
 991	return comp_ret == 0 && alloc_ret == 0;
 992}
 993
 994static void zswap_decompress(struct zswap_entry *entry, struct folio *folio)
 995{
 996	struct zpool *zpool = entry->pool->zpool;
 997	struct scatterlist input, output;
 998	struct crypto_acomp_ctx *acomp_ctx;
 999	u8 *src;
1000
1001	acomp_ctx = acomp_ctx_get_cpu_lock(entry->pool);
1002	src = zpool_map_handle(zpool, entry->handle, ZPOOL_MM_RO);
1003	/*
1004	 * If zpool_map_handle is atomic, we cannot reliably utilize its mapped buffer
1005	 * to do crypto_acomp_decompress() which might sleep. In such cases, we must
1006	 * resort to copying the buffer to a temporary one.
1007	 * Meanwhile, zpool_map_handle() might return a non-linearly mapped buffer,
1008	 * such as a kmap address of high memory or even ever a vmap address.
1009	 * However, sg_init_one is only equipped to handle linearly mapped low memory.
1010	 * In such cases, we also must copy the buffer to a temporary and lowmem one.
1011	 */
1012	if ((acomp_ctx->is_sleepable && !zpool_can_sleep_mapped(zpool)) ||
1013	    !virt_addr_valid(src)) {
1014		memcpy(acomp_ctx->buffer, src, entry->length);
1015		src = acomp_ctx->buffer;
1016		zpool_unmap_handle(zpool, entry->handle);
1017	}
1018
1019	sg_init_one(&input, src, entry->length);
1020	sg_init_table(&output, 1);
1021	sg_set_folio(&output, folio, PAGE_SIZE, 0);
1022	acomp_request_set_params(acomp_ctx->req, &input, &output, entry->length, PAGE_SIZE);
1023	BUG_ON(crypto_wait_req(crypto_acomp_decompress(acomp_ctx->req), &acomp_ctx->wait));
1024	BUG_ON(acomp_ctx->req->dlen != PAGE_SIZE);
1025
1026	if (src != acomp_ctx->buffer)
1027		zpool_unmap_handle(zpool, entry->handle);
1028	acomp_ctx_put_unlock(acomp_ctx);
1029}
1030
1031/*********************************
1032* writeback code
1033**********************************/
1034/*
1035 * Attempts to free an entry by adding a folio to the swap cache,
1036 * decompressing the entry data into the folio, and issuing a
1037 * bio write to write the folio back to the swap device.
1038 *
1039 * This can be thought of as a "resumed writeback" of the folio
1040 * to the swap device.  We are basically resuming the same swap
1041 * writeback path that was intercepted with the zswap_store()
1042 * in the first place.  After the folio has been decompressed into
1043 * the swap cache, the compressed version stored by zswap can be
1044 * freed.
1045 */
1046static int zswap_writeback_entry(struct zswap_entry *entry,
1047				 swp_entry_t swpentry)
1048{
1049	struct xarray *tree;
1050	pgoff_t offset = swp_offset(swpentry);
1051	struct folio *folio;
1052	struct mempolicy *mpol;
1053	bool folio_was_allocated;
 
 
 
 
 
1054	struct writeback_control wbc = {
1055		.sync_mode = WB_SYNC_NONE,
1056	};
1057
1058	/* try to allocate swap cache folio */
1059	mpol = get_task_policy(current);
1060	folio = __read_swap_cache_async(swpentry, GFP_KERNEL, mpol,
1061				NO_INTERLEAVE_INDEX, &folio_was_allocated, true);
1062	if (!folio)
1063		return -ENOMEM;
1064
1065	/*
1066	 * Found an existing folio, we raced with swapin or concurrent
1067	 * shrinker. We generally writeback cold folios from zswap, and
1068	 * swapin means the folio just became hot, so skip this folio.
1069	 * For unlikely concurrent shrinker case, it will be unlinked
1070	 * and freed when invalidated by the concurrent shrinker anyway.
1071	 */
1072	if (!folio_was_allocated) {
1073		folio_put(folio);
1074		return -EEXIST;
1075	}
1076
1077	/*
1078	 * folio is locked, and the swapcache is now secured against
1079	 * concurrent swapping to and from the slot, and concurrent
1080	 * swapoff so we can safely dereference the zswap tree here.
1081	 * Verify that the swap entry hasn't been invalidated and recycled
1082	 * behind our backs, to avoid overwriting a new swap folio with
1083	 * old compressed data. Only when this is successful can the entry
1084	 * be dereferenced.
1085	 */
1086	tree = swap_zswap_tree(swpentry);
1087	if (entry != xa_cmpxchg(tree, offset, entry, NULL, GFP_KERNEL)) {
1088		delete_from_swap_cache(folio);
1089		folio_unlock(folio);
1090		folio_put(folio);
1091		return -ENOMEM;
1092	}
 
 
1093
1094	zswap_decompress(entry, folio);
 
 
 
 
1095
1096	count_vm_event(ZSWPWB);
1097	if (entry->objcg)
1098		count_objcg_events(entry->objcg, ZSWPWB, 1);
 
 
1099
1100	zswap_entry_free(entry);
 
 
 
 
 
 
 
 
 
 
 
1101
1102	/* folio is up to date */
1103	folio_mark_uptodate(folio);
 
1104
1105	/* move it to the tail of the inactive list after end_writeback */
1106	folio_set_reclaim(folio);
1107
1108	/* start writeback */
1109	__swap_writepage(folio, &wbc);
1110	folio_put(folio);
1111
1112	return 0;
1113}
1114
1115/*********************************
1116* shrinker functions
1117**********************************/
1118/*
1119 * The dynamic shrinker is modulated by the following factors:
1120 *
1121 * 1. Each zswap entry has a referenced bit, which the shrinker unsets (giving
1122 *    the entry a second chance) before rotating it in the LRU list. If the
1123 *    entry is considered again by the shrinker, with its referenced bit unset,
1124 *    it is written back. The writeback rate as a result is dynamically
1125 *    adjusted by the pool activities - if the pool is dominated by new entries
1126 *    (i.e lots of recent zswapouts), these entries will be protected and
1127 *    the writeback rate will slow down. On the other hand, if the pool has a
1128 *    lot of stagnant entries, these entries will be reclaimed immediately,
1129 *    effectively increasing the writeback rate.
1130 *
1131 * 2. Swapins counter: If we observe swapins, it is a sign that we are
1132 *    overshrinking and should slow down. We maintain a swapins counter, which
1133 *    is consumed and subtract from the number of eligible objects on the LRU
1134 *    in zswap_shrinker_count().
1135 *
1136 * 3. Compression ratio. The better the workload compresses, the less gains we
1137 *    can expect from writeback. We scale down the number of objects available
1138 *    for reclaim by this ratio.
1139 */
1140static enum lru_status shrink_memcg_cb(struct list_head *item, struct list_lru_one *l,
1141				       void *arg)
1142{
1143	struct zswap_entry *entry = container_of(item, struct zswap_entry, lru);
1144	bool *encountered_page_in_swapcache = (bool *)arg;
1145	swp_entry_t swpentry;
1146	enum lru_status ret = LRU_REMOVED_RETRY;
1147	int writeback_result;
1148
1149	/*
1150	 * Second chance algorithm: if the entry has its referenced bit set, give it
1151	 * a second chance. Only clear the referenced bit and rotate it in the
1152	 * zswap's LRU list.
1153	 */
1154	if (entry->referenced) {
1155		entry->referenced = false;
1156		return LRU_ROTATE;
1157	}
1158
1159	/*
1160	 * As soon as we drop the LRU lock, the entry can be freed by
1161	 * a concurrent invalidation. This means the following:
1162	 *
1163	 * 1. We extract the swp_entry_t to the stack, allowing
1164	 *    zswap_writeback_entry() to pin the swap entry and
1165	 *    then validate the zwap entry against that swap entry's
1166	 *    tree using pointer value comparison. Only when that
1167	 *    is successful can the entry be dereferenced.
1168	 *
1169	 * 2. Usually, objects are taken off the LRU for reclaim. In
1170	 *    this case this isn't possible, because if reclaim fails
1171	 *    for whatever reason, we have no means of knowing if the
1172	 *    entry is alive to put it back on the LRU.
1173	 *
1174	 *    So rotate it before dropping the lock. If the entry is
1175	 *    written back or invalidated, the free path will unlink
1176	 *    it. For failures, rotation is the right thing as well.
1177	 *
1178	 *    Temporary failures, where the same entry should be tried
1179	 *    again immediately, almost never happen for this shrinker.
1180	 *    We don't do any trylocking; -ENOMEM comes closest,
1181	 *    but that's extremely rare and doesn't happen spuriously
1182	 *    either. Don't bother distinguishing this case.
1183	 */
1184	list_move_tail(item, &l->list);
1185
1186	/*
1187	 * Once the lru lock is dropped, the entry might get freed. The
1188	 * swpentry is copied to the stack, and entry isn't deref'd again
1189	 * until the entry is verified to still be alive in the tree.
1190	 */
1191	swpentry = entry->swpentry;
1192
1193	/*
1194	 * It's safe to drop the lock here because we return either
1195	 * LRU_REMOVED_RETRY or LRU_RETRY.
1196	 */
1197	spin_unlock(&l->lock);
1198
1199	writeback_result = zswap_writeback_entry(entry, swpentry);
1200
1201	if (writeback_result) {
1202		zswap_reject_reclaim_fail++;
1203		ret = LRU_RETRY;
1204
1205		/*
1206		 * Encountering a page already in swap cache is a sign that we are shrinking
1207		 * into the warmer region. We should terminate shrinking (if we're in the dynamic
1208		 * shrinker context).
1209		 */
1210		if (writeback_result == -EEXIST && encountered_page_in_swapcache) {
1211			ret = LRU_STOP;
1212			*encountered_page_in_swapcache = true;
1213		}
1214	} else {
1215		zswap_written_back_pages++;
1216	}
1217
 
 
1218	return ret;
1219}
1220
1221static unsigned long zswap_shrinker_scan(struct shrinker *shrinker,
1222		struct shrink_control *sc)
1223{
1224	unsigned long shrink_ret;
1225	bool encountered_page_in_swapcache = false;
1226
1227	if (!zswap_shrinker_enabled ||
1228			!mem_cgroup_zswap_writeback_enabled(sc->memcg)) {
1229		sc->nr_scanned = 0;
1230		return SHRINK_STOP;
1231	}
1232
1233	shrink_ret = list_lru_shrink_walk(&zswap_list_lru, sc, &shrink_memcg_cb,
1234		&encountered_page_in_swapcache);
1235
1236	if (encountered_page_in_swapcache)
1237		return SHRINK_STOP;
1238
1239	return shrink_ret ? shrink_ret : SHRINK_STOP;
1240}
1241
1242static unsigned long zswap_shrinker_count(struct shrinker *shrinker,
1243		struct shrink_control *sc)
1244{
1245	struct mem_cgroup *memcg = sc->memcg;
1246	struct lruvec *lruvec = mem_cgroup_lruvec(memcg, NODE_DATA(sc->nid));
1247	atomic_long_t *nr_disk_swapins =
1248		&lruvec->zswap_lruvec_state.nr_disk_swapins;
1249	unsigned long nr_backing, nr_stored, nr_freeable, nr_disk_swapins_cur,
1250		nr_remain;
1251
1252	if (!zswap_shrinker_enabled || !mem_cgroup_zswap_writeback_enabled(memcg))
1253		return 0;
1254
1255	/*
1256	 * The shrinker resumes swap writeback, which will enter block
1257	 * and may enter fs. XXX: Harmonize with vmscan.c __GFP_FS
1258	 * rules (may_enter_fs()), which apply on a per-folio basis.
1259	 */
1260	if (!gfp_has_io_fs(sc->gfp_mask))
1261		return 0;
1262
1263	/*
1264	 * For memcg, use the cgroup-wide ZSWAP stats since we don't
1265	 * have them per-node and thus per-lruvec. Careful if memcg is
1266	 * runtime-disabled: we can get sc->memcg == NULL, which is ok
1267	 * for the lruvec, but not for memcg_page_state().
1268	 *
1269	 * Without memcg, use the zswap pool-wide metrics.
1270	 */
1271	if (!mem_cgroup_disabled()) {
1272		mem_cgroup_flush_stats(memcg);
1273		nr_backing = memcg_page_state(memcg, MEMCG_ZSWAP_B) >> PAGE_SHIFT;
1274		nr_stored = memcg_page_state(memcg, MEMCG_ZSWAPPED);
1275	} else {
1276		nr_backing = zswap_total_pages();
1277		nr_stored = atomic_long_read(&zswap_stored_pages);
1278	}
1279
1280	if (!nr_stored)
1281		return 0;
1282
1283	nr_freeable = list_lru_shrink_count(&zswap_list_lru, sc);
1284	if (!nr_freeable)
1285		return 0;
1286
1287	/*
1288	 * Subtract from the lru size the number of pages that are recently swapped
1289	 * in from disk. The idea is that had we protect the zswap's LRU by this
1290	 * amount of pages, these disk swapins would not have happened.
1291	 */
1292	nr_disk_swapins_cur = atomic_long_read(nr_disk_swapins);
1293	do {
1294		if (nr_freeable >= nr_disk_swapins_cur)
1295			nr_remain = 0;
1296		else
1297			nr_remain = nr_disk_swapins_cur - nr_freeable;
1298	} while (!atomic_long_try_cmpxchg(
1299		nr_disk_swapins, &nr_disk_swapins_cur, nr_remain));
1300
1301	nr_freeable -= nr_disk_swapins_cur - nr_remain;
1302	if (!nr_freeable)
1303		return 0;
1304
1305	/*
1306	 * Scale the number of freeable pages by the memory saving factor.
1307	 * This ensures that the better zswap compresses memory, the fewer
1308	 * pages we will evict to swap (as it will otherwise incur IO for
1309	 * relatively small memory saving).
1310	 */
1311	return mult_frac(nr_freeable, nr_backing, nr_stored);
1312}
1313
1314static struct shrinker *zswap_alloc_shrinker(void)
1315{
1316	struct shrinker *shrinker;
1317
1318	shrinker =
1319		shrinker_alloc(SHRINKER_NUMA_AWARE | SHRINKER_MEMCG_AWARE, "mm-zswap");
1320	if (!shrinker)
1321		return NULL;
1322
1323	shrinker->scan_objects = zswap_shrinker_scan;
1324	shrinker->count_objects = zswap_shrinker_count;
1325	shrinker->batch = 0;
1326	shrinker->seeks = DEFAULT_SEEKS;
1327	return shrinker;
1328}
1329
1330static int shrink_memcg(struct mem_cgroup *memcg)
1331{
1332	int nid, shrunk = 0, scanned = 0;
1333
1334	if (!mem_cgroup_zswap_writeback_enabled(memcg))
1335		return -ENOENT;
1336
1337	/*
1338	 * Skip zombies because their LRUs are reparented and we would be
1339	 * reclaiming from the parent instead of the dead memcg.
1340	 */
1341	if (memcg && !mem_cgroup_online(memcg))
1342		return -ENOENT;
1343
1344	for_each_node_state(nid, N_NORMAL_MEMORY) {
1345		unsigned long nr_to_walk = 1;
1346
1347		shrunk += list_lru_walk_one(&zswap_list_lru, nid, memcg,
1348					    &shrink_memcg_cb, NULL, &nr_to_walk);
1349		scanned += 1 - nr_to_walk;
1350	}
1351
1352	if (!scanned)
1353		return -ENOENT;
1354
1355	return shrunk ? 0 : -EAGAIN;
1356}
1357
1358static void shrink_worker(struct work_struct *w)
1359{
1360	struct mem_cgroup *memcg;
1361	int ret, failures = 0, attempts = 0;
1362	unsigned long thr;
1363
1364	/* Reclaim down to the accept threshold */
1365	thr = zswap_accept_thr_pages();
1366
1367	/*
1368	 * Global reclaim will select cgroup in a round-robin fashion from all
1369	 * online memcgs, but memcgs that have no pages in zswap and
1370	 * writeback-disabled memcgs (memory.zswap.writeback=0) are not
1371	 * candidates for shrinking.
1372	 *
1373	 * Shrinking will be aborted if we encounter the following
1374	 * MAX_RECLAIM_RETRIES times:
1375	 * - No writeback-candidate memcgs found in a memcg tree walk.
1376	 * - Shrinking a writeback-candidate memcg failed.
1377	 *
1378	 * We save iteration cursor memcg into zswap_next_shrink,
1379	 * which can be modified by the offline memcg cleaner
1380	 * zswap_memcg_offline_cleanup().
1381	 *
1382	 * Since the offline cleaner is called only once, we cannot leave an
1383	 * offline memcg reference in zswap_next_shrink.
1384	 * We can rely on the cleaner only if we get online memcg under lock.
1385	 *
1386	 * If we get an offline memcg, we cannot determine if the cleaner has
1387	 * already been called or will be called later. We must put back the
1388	 * reference before returning from this function. Otherwise, the
1389	 * offline memcg left in zswap_next_shrink will hold the reference
1390	 * until the next run of shrink_worker().
1391	 */
1392	do {
1393		/*
1394		 * Start shrinking from the next memcg after zswap_next_shrink.
1395		 * When the offline cleaner has already advanced the cursor,
1396		 * advancing the cursor here overlooks one memcg, but this
1397		 * should be negligibly rare.
1398		 *
1399		 * If we get an online memcg, keep the extra reference in case
1400		 * the original one obtained by mem_cgroup_iter() is dropped by
1401		 * zswap_memcg_offline_cleanup() while we are shrinking the
1402		 * memcg.
1403		 */
1404		spin_lock(&zswap_shrink_lock);
1405		do {
1406			memcg = mem_cgroup_iter(NULL, zswap_next_shrink, NULL);
1407			zswap_next_shrink = memcg;
1408		} while (memcg && !mem_cgroup_tryget_online(memcg));
1409		spin_unlock(&zswap_shrink_lock);
1410
1411		if (!memcg) {
1412			/*
1413			 * Continue shrinking without incrementing failures if
1414			 * we found candidate memcgs in the last tree walk.
1415			 */
1416			if (!attempts && ++failures == MAX_RECLAIM_RETRIES)
1417				break;
1418
1419			attempts = 0;
1420			goto resched;
1421		}
1422
1423		ret = shrink_memcg(memcg);
1424		/* drop the extra reference */
1425		mem_cgroup_put(memcg);
1426
1427		/*
1428		 * There are no writeback-candidate pages in the memcg.
1429		 * This is not an issue as long as we can find another memcg
1430		 * with pages in zswap. Skip this without incrementing attempts
1431		 * and failures.
1432		 */
1433		if (ret == -ENOENT)
1434			continue;
1435		++attempts;
1436
1437		if (ret && ++failures == MAX_RECLAIM_RETRIES)
1438			break;
1439resched:
1440		cond_resched();
1441	} while (zswap_total_pages() > thr);
1442}
1443
1444/*********************************
1445* main API
1446**********************************/
 
 
 
 
 
 
 
 
 
 
 
 
 
 
1447
1448static bool zswap_store_page(struct page *page,
1449			     struct obj_cgroup *objcg,
1450			     struct zswap_pool *pool)
1451{
1452	swp_entry_t page_swpentry = page_swap_entry(page);
1453	struct zswap_entry *entry, *old;
1454
1455	/* allocate entry */
1456	entry = zswap_entry_cache_alloc(GFP_KERNEL, page_to_nid(page));
1457	if (!entry) {
1458		zswap_reject_kmemcache_fail++;
1459		return false;
1460	}
1461
1462	if (!zswap_compress(page, entry, pool))
1463		goto compress_failed;
1464
1465	old = xa_store(swap_zswap_tree(page_swpentry),
1466		       swp_offset(page_swpentry),
1467		       entry, GFP_KERNEL);
1468	if (xa_is_err(old)) {
1469		int err = xa_err(old);
1470
1471		WARN_ONCE(err != -ENOMEM, "unexpected xarray error: %d\n", err);
1472		zswap_reject_alloc_fail++;
1473		goto store_failed;
1474	}
1475
1476	/*
1477	 * We may have had an existing entry that became stale when
1478	 * the folio was redirtied and now the new version is being
1479	 * swapped out. Get rid of the old.
1480	 */
1481	if (old)
1482		zswap_entry_free(old);
1483
1484	/*
1485	 * The entry is successfully compressed and stored in the tree, there is
1486	 * no further possibility of failure. Grab refs to the pool and objcg,
1487	 * charge zswap memory, and increment zswap_stored_pages.
1488	 * The opposite actions will be performed by zswap_entry_free()
1489	 * when the entry is removed from the tree.
1490	 */
1491	zswap_pool_get(pool);
1492	if (objcg) {
1493		obj_cgroup_get(objcg);
1494		obj_cgroup_charge_zswap(objcg, entry->length);
1495	}
1496	atomic_long_inc(&zswap_stored_pages);
1497
1498	/*
1499	 * We finish initializing the entry while it's already in xarray.
1500	 * This is safe because:
1501	 *
1502	 * 1. Concurrent stores and invalidations are excluded by folio lock.
1503	 *
1504	 * 2. Writeback is excluded by the entry not being on the LRU yet.
1505	 *    The publishing order matters to prevent writeback from seeing
1506	 *    an incoherent entry.
1507	 */
1508	entry->pool = pool;
1509	entry->swpentry = page_swpentry;
1510	entry->objcg = objcg;
1511	entry->referenced = true;
1512	if (entry->length) {
1513		INIT_LIST_HEAD(&entry->lru);
1514		zswap_lru_add(&zswap_list_lru, entry);
1515	}
1516
1517	return true;
1518
1519store_failed:
1520	zpool_free(pool->zpool, entry->handle);
1521compress_failed:
1522	zswap_entry_cache_free(entry);
1523	return false;
1524}
1525
1526bool zswap_store(struct folio *folio)
1527{
1528	long nr_pages = folio_nr_pages(folio);
1529	swp_entry_t swp = folio->swap;
1530	struct obj_cgroup *objcg = NULL;
1531	struct mem_cgroup *memcg = NULL;
1532	struct zswap_pool *pool;
1533	bool ret = false;
1534	long index;
1535
1536	VM_WARN_ON_ONCE(!folio_test_locked(folio));
1537	VM_WARN_ON_ONCE(!folio_test_swapcache(folio));
1538
1539	if (!zswap_enabled)
1540		goto check_old;
1541
1542	objcg = get_obj_cgroup_from_folio(folio);
1543	if (objcg && !obj_cgroup_may_zswap(objcg)) {
1544		memcg = get_mem_cgroup_from_objcg(objcg);
1545		if (shrink_memcg(memcg)) {
1546			mem_cgroup_put(memcg);
1547			goto put_objcg;
 
 
 
1548		}
1549		mem_cgroup_put(memcg);
1550	}
1551
1552	if (zswap_check_limits())
1553		goto put_objcg;
1554
1555	pool = zswap_pool_current_get();
1556	if (!pool)
1557		goto put_objcg;
1558
1559	if (objcg) {
1560		memcg = get_mem_cgroup_from_objcg(objcg);
1561		if (memcg_list_lru_alloc(memcg, &zswap_list_lru, GFP_KERNEL)) {
1562			mem_cgroup_put(memcg);
1563			goto put_pool;
1564		}
1565		mem_cgroup_put(memcg);
1566	}
1567
1568	for (index = 0; index < nr_pages; ++index) {
1569		struct page *page = folio_page(folio, index);
 
 
 
 
 
 
 
 
 
1570
1571		if (!zswap_store_page(page, objcg, pool))
1572			goto put_pool;
 
 
 
 
 
 
 
 
 
 
 
1573	}
 
 
 
 
 
1574
1575	if (objcg)
1576		count_objcg_events(objcg, ZSWPOUT, nr_pages);
 
 
1577
1578	count_vm_events(ZSWPOUT, nr_pages);
 
 
 
 
 
 
 
 
 
 
 
 
1579
1580	ret = true;
 
 
1581
1582put_pool:
1583	zswap_pool_put(pool);
1584put_objcg:
1585	obj_cgroup_put(objcg);
1586	if (!ret && zswap_pool_reached_full)
1587		queue_work(shrink_wq, &zswap_shrink_work);
1588check_old:
1589	/*
1590	 * If the zswap store fails or zswap is disabled, we must invalidate
1591	 * the possibly stale entries which were previously stored at the
1592	 * offsets corresponding to each page of the folio. Otherwise,
1593	 * writeback could overwrite the new data in the swapfile.
1594	 */
1595	if (!ret) {
1596		unsigned type = swp_type(swp);
1597		pgoff_t offset = swp_offset(swp);
1598		struct zswap_entry *entry;
1599		struct xarray *tree;
1600
1601		for (index = 0; index < nr_pages; ++index) {
1602			tree = swap_zswap_tree(swp_entry(type, offset + index));
1603			entry = xa_erase(tree, offset + index);
1604			if (entry)
1605				zswap_entry_free(entry);
1606		}
1607	}
1608
 
 
 
 
 
 
1609	return ret;
1610}
1611
1612bool zswap_load(struct folio *folio)
 
 
 
 
 
1613{
1614	swp_entry_t swp = folio->swap;
1615	pgoff_t offset = swp_offset(swp);
1616	bool swapcache = folio_test_swapcache(folio);
1617	struct xarray *tree = swap_zswap_tree(swp);
1618	struct zswap_entry *entry;
 
 
 
 
1619
1620	VM_WARN_ON_ONCE(!folio_test_locked(folio));
1621
1622	if (zswap_never_enabled())
1623		return false;
1624
1625	/*
1626	 * Large folios should not be swapped in while zswap is being used, as
1627	 * they are not properly handled. Zswap does not properly load large
1628	 * folios, and a large folio may only be partially in zswap.
1629	 *
1630	 * Return true without marking the folio uptodate so that an IO error is
1631	 * emitted (e.g. do_swap_page() will sigbus).
1632	 */
1633	if (WARN_ON_ONCE(folio_test_large(folio)))
1634		return true;
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
1635
1636	/*
1637	 * When reading into the swapcache, invalidate our entry. The
1638	 * swapcache can be the authoritative owner of the page and
1639	 * its mappings, and the pressure that results from having two
1640	 * in-memory copies outweighs any benefits of caching the
1641	 * compression work.
1642	 *
1643	 * (Most swapins go through the swapcache. The notable
1644	 * exception is the singleton fault on SWP_SYNCHRONOUS_IO
1645	 * files, which reads into a private page and may free it if
1646	 * the fault fails. We remain the primary owner of the entry.)
1647	 */
1648	if (swapcache)
1649		entry = xa_erase(tree, offset);
1650	else
1651		entry = xa_load(tree, offset);
1652
1653	if (!entry)
1654		return false;
 
 
 
1655
1656	zswap_decompress(entry, folio);
 
 
 
 
 
 
 
1657
1658	count_vm_event(ZSWPIN);
1659	if (entry->objcg)
1660		count_objcg_events(entry->objcg, ZSWPIN, 1);
1661
1662	if (swapcache) {
1663		zswap_entry_free(entry);
1664		folio_mark_dirty(folio);
1665	}
1666
1667	folio_mark_uptodate(folio);
1668	return true;
1669}
1670
1671void zswap_invalidate(swp_entry_t swp)
 
1672{
1673	pgoff_t offset = swp_offset(swp);
1674	struct xarray *tree = swap_zswap_tree(swp);
1675	struct zswap_entry *entry;
1676
1677	if (xa_empty(tree))
1678		return;
1679
1680	entry = xa_erase(tree, offset);
1681	if (entry)
1682		zswap_entry_free(entry);
 
 
 
 
 
1683}
1684
1685int zswap_swapon(int type, unsigned long nr_pages)
1686{
1687	struct xarray *trees, *tree;
1688	unsigned int nr, i;
1689
1690	nr = DIV_ROUND_UP(nr_pages, SWAP_ADDRESS_SPACE_PAGES);
1691	trees = kvcalloc(nr, sizeof(*tree), GFP_KERNEL);
1692	if (!trees) {
1693		pr_err("alloc failed, zswap disabled for swap type %d\n", type);
1694		return -ENOMEM;
1695	}
1696
1697	for (i = 0; i < nr; i++)
1698		xa_init(trees + i);
1699
1700	nr_zswap_trees[type] = nr;
1701	zswap_trees[type] = trees;
1702	return 0;
1703}
1704
1705void zswap_swapoff(int type)
1706{
1707	struct xarray *trees = zswap_trees[type];
1708	unsigned int i;
1709
1710	if (!trees)
1711		return;
1712
1713	/* try_to_unuse() invalidated all the entries already */
1714	for (i = 0; i < nr_zswap_trees[type]; i++)
1715		WARN_ON_ONCE(!xa_empty(trees + i));
1716
1717	kvfree(trees);
1718	nr_zswap_trees[type] = 0;
1719	zswap_trees[type] = NULL;
1720}
1721
1722/*********************************
1723* debugfs functions
1724**********************************/
1725#ifdef CONFIG_DEBUG_FS
1726#include <linux/debugfs.h>
1727
1728static struct dentry *zswap_debugfs_root;
1729
1730static int debugfs_get_total_size(void *data, u64 *val)
1731{
1732	*val = zswap_total_pages() * PAGE_SIZE;
1733	return 0;
1734}
1735DEFINE_DEBUGFS_ATTRIBUTE(total_size_fops, debugfs_get_total_size, NULL, "%llu\n");
1736
1737static int debugfs_get_stored_pages(void *data, u64 *val)
1738{
1739	*val = atomic_long_read(&zswap_stored_pages);
1740	return 0;
1741}
1742DEFINE_DEBUGFS_ATTRIBUTE(stored_pages_fops, debugfs_get_stored_pages, NULL, "%llu\n");
1743
1744static int zswap_debugfs_init(void)
1745{
1746	if (!debugfs_initialized())
1747		return -ENODEV;
1748
1749	zswap_debugfs_root = debugfs_create_dir("zswap", NULL);
1750
1751	debugfs_create_u64("pool_limit_hit", 0444,
1752			   zswap_debugfs_root, &zswap_pool_limit_hit);
1753	debugfs_create_u64("reject_reclaim_fail", 0444,
1754			   zswap_debugfs_root, &zswap_reject_reclaim_fail);
1755	debugfs_create_u64("reject_alloc_fail", 0444,
1756			   zswap_debugfs_root, &zswap_reject_alloc_fail);
1757	debugfs_create_u64("reject_kmemcache_fail", 0444,
1758			   zswap_debugfs_root, &zswap_reject_kmemcache_fail);
1759	debugfs_create_u64("reject_compress_fail", 0444,
1760			   zswap_debugfs_root, &zswap_reject_compress_fail);
1761	debugfs_create_u64("reject_compress_poor", 0444,
1762			   zswap_debugfs_root, &zswap_reject_compress_poor);
1763	debugfs_create_u64("written_back_pages", 0444,
1764			   zswap_debugfs_root, &zswap_written_back_pages);
1765	debugfs_create_file("pool_total_size", 0444,
1766			    zswap_debugfs_root, NULL, &total_size_fops);
1767	debugfs_create_file("stored_pages", 0444,
1768			    zswap_debugfs_root, NULL, &stored_pages_fops);
 
 
 
 
1769
1770	return 0;
1771}
 
 
 
 
 
1772#else
1773static int zswap_debugfs_init(void)
1774{
1775	return 0;
1776}
 
 
1777#endif
1778
1779/*********************************
1780* module init and exit
1781**********************************/
1782static int zswap_setup(void)
1783{
1784	struct zswap_pool *pool;
1785	int ret;
1786
1787	zswap_entry_cache = KMEM_CACHE(zswap_entry, 0);
1788	if (!zswap_entry_cache) {
 
1789		pr_err("entry cache creation failed\n");
1790		goto cache_fail;
1791	}
1792
 
 
 
 
 
 
 
1793	ret = cpuhp_setup_state_multi(CPUHP_MM_ZSWP_POOL_PREPARE,
1794				      "mm/zswap_pool:prepare",
1795				      zswap_cpu_comp_prepare,
1796				      zswap_cpu_comp_dead);
1797	if (ret)
1798		goto hp_fail;
1799
1800	shrink_wq = alloc_workqueue("zswap-shrink",
1801			WQ_UNBOUND|WQ_MEM_RECLAIM, 1);
1802	if (!shrink_wq)
1803		goto shrink_wq_fail;
1804
1805	zswap_shrinker = zswap_alloc_shrinker();
1806	if (!zswap_shrinker)
1807		goto shrinker_fail;
1808	if (list_lru_init_memcg(&zswap_list_lru, zswap_shrinker))
1809		goto lru_fail;
1810	shrinker_register(zswap_shrinker);
1811
1812	INIT_WORK(&zswap_shrink_work, shrink_worker);
1813
1814	pool = __zswap_pool_create_fallback();
1815	if (pool) {
1816		pr_info("loaded using pool %s/%s\n", pool->tfm_name,
1817			zpool_get_type(pool->zpool));
1818		list_add(&pool->list, &zswap_pools);
1819		zswap_has_pool = true;
1820		static_branch_enable(&zswap_ever_enabled);
1821	} else {
1822		pr_err("pool creation failed\n");
1823		zswap_enabled = false;
1824	}
1825
 
 
 
 
 
1826	if (zswap_debugfs_init())
1827		pr_warn("debugfs initialization failed\n");
1828	zswap_init_state = ZSWAP_INIT_SUCCEED;
1829	return 0;
1830
1831lru_fail:
1832	shrinker_free(zswap_shrinker);
1833shrinker_fail:
1834	destroy_workqueue(shrink_wq);
1835shrink_wq_fail:
1836	cpuhp_remove_multi_state(CPUHP_MM_ZSWP_POOL_PREPARE);
1837hp_fail:
1838	kmem_cache_destroy(zswap_entry_cache);
 
 
1839cache_fail:
1840	/* if built-in, we aren't unloaded on failure; don't allow use */
1841	zswap_init_state = ZSWAP_INIT_FAILED;
1842	zswap_enabled = false;
1843	return -ENOMEM;
1844}
1845
1846static int __init zswap_init(void)
1847{
1848	if (!zswap_enabled)
1849		return 0;
1850	return zswap_setup();
1851}
1852/* must be late so crypto has time to come up */
1853late_initcall(zswap_init);
1854
 
1855MODULE_AUTHOR("Seth Jennings <sjennings@variantweb.net>");
1856MODULE_DESCRIPTION("Compressed cache for swap pages");