[linux.git] / mm / swap_slots.c

// SPDX-License-Identifier: GPL-2.0
/*
 * Manage cache of swap slots to be used for and returned from
 * swap.
 *
 * Copyright(c) 2016 Intel Corporation.
 *
 * Author: Tim Chen <[email protected]>
 *
 * We allocate the swap slots from the global pool and put
 * it into local per cpu caches.  This has the advantage
 * of no needing to acquire the swap_info lock every time
 * we need a new slot.
 *
 * There is also opportunity to simply return the slot
 * to local caches without needing to acquire swap_info
 * lock.  We do not reuse the returned slots directly but
 * move them back to the global pool in a batch.  This
 * allows the slots to coaellesce and reduce fragmentation.
 *
 * The swap entry allocated is marked with SWAP_HAS_CACHE
 * flag in map_count that prevents it from being allocated
 * again from the global pool.
 *
 * The swap slots cache is protected by a mutex instead of
 * a spin lock as when we search for slots with scan_swap_map,
 * we can possibly sleep.
 */

#include <linux/swap_slots.h>
#include <linux/cpu.h>
#include <linux/cpumask.h>
#include <linux/vmalloc.h>
#include <linux/mutex.h>
#include <linux/mm.h>

static DEFINE_PER_CPU(struct swap_slots_cache, swp_slots);
static bool	swap_slot_cache_active;
bool	swap_slot_cache_enabled;
static bool	swap_slot_cache_initialized;
static DEFINE_MUTEX(swap_slots_cache_mutex);
/* Serialize swap slots cache enable/disable operations */
static DEFINE_MUTEX(swap_slots_cache_enable_mutex);

static void __drain_swap_slots_cache(unsigned int type);
static void deactivate_swap_slots_cache(void);
static void reactivate_swap_slots_cache(void);

#define use_swap_slot_cache (swap_slot_cache_active && swap_slot_cache_enabled)
#define SLOTS_CACHE 0x1
#define SLOTS_CACHE_RET 0x2

static void deactivate_swap_slots_cache(void)
{
	mutex_lock(&swap_slots_cache_mutex);
	swap_slot_cache_active = false;
	__drain_swap_slots_cache(SLOTS_CACHE|SLOTS_CACHE_RET);
	mutex_unlock(&swap_slots_cache_mutex);
}

static void reactivate_swap_slots_cache(void)
{
	mutex_lock(&swap_slots_cache_mutex);
	swap_slot_cache_active = true;
	mutex_unlock(&swap_slots_cache_mutex);
}

/* Must not be called with cpu hot plug lock */
void disable_swap_slots_cache_lock(void)
{
	mutex_lock(&swap_slots_cache_enable_mutex);
	swap_slot_cache_enabled = false;
	if (swap_slot_cache_initialized) {
		/* serialize with cpu hotplug operations */
		get_online_cpus();
		__drain_swap_slots_cache(SLOTS_CACHE|SLOTS_CACHE_RET);
		put_online_cpus();
	}
}

static void __reenable_swap_slots_cache(void)
{
	swap_slot_cache_enabled = has_usable_swap();
}

void reenable_swap_slots_cache_unlock(void)
{
	__reenable_swap_slots_cache();
	mutex_unlock(&swap_slots_cache_enable_mutex);
}

static bool check_cache_active(void)
{
	long pages;

	if (!swap_slot_cache_enabled)
		return false;

	pages = get_nr_swap_pages();
	if (!swap_slot_cache_active) {
		if (pages > num_online_cpus() *
		    THRESHOLD_ACTIVATE_SWAP_SLOTS_CACHE)
			reactivate_swap_slots_cache();
		goto out;
	}

	/* if global pool of slot caches too low, deactivate cache */
	if (pages < num_online_cpus() * THRESHOLD_DEACTIVATE_SWAP_SLOTS_CACHE)
		deactivate_swap_slots_cache();
out:
	return swap_slot_cache_active;
}

static int alloc_swap_slot_cache(unsigned int cpu)
{
	struct swap_slots_cache *cache;
	swp_entry_t *slots, *slots_ret;

	/*
	 * Do allocation outside swap_slots_cache_mutex
	 * as kvzalloc could trigger reclaim and get_swap_page,
	 * which can lock swap_slots_cache_mutex.
	 */
	slots = kvcalloc(SWAP_SLOTS_CACHE_SIZE, sizeof(swp_entry_t),
			 GFP_KERNEL);
	if (!slots)
		return -ENOMEM;

	slots_ret = kvcalloc(SWAP_SLOTS_CACHE_SIZE, sizeof(swp_entry_t),
			     GFP_KERNEL);
	if (!slots_ret) {
		kvfree(slots);
		return -ENOMEM;
	}

	mutex_lock(&swap_slots_cache_mutex);
	cache = &per_cpu(swp_slots, cpu);
	if (cache->slots || cache->slots_ret) {
		/* cache already allocated */
		mutex_unlock(&swap_slots_cache_mutex);

		kvfree(slots);
		kvfree(slots_ret);

		return 0;
	}

	if (!cache->lock_initialized) {
		mutex_init(&cache->alloc_lock);
		spin_lock_init(&cache->free_lock);
		cache->lock_initialized = true;
	}
	cache->nr = 0;
	cache->cur = 0;
	cache->n_ret = 0;
	/*
	 * We initialized alloc_lock and free_lock earlier.  We use
	 * !cache->slots or !cache->slots_ret to know if it is safe to acquire
	 * the corresponding lock and use the cache.  Memory barrier below
	 * ensures the assumption.
	 */
	mb();
	cache->slots = slots;
	cache->slots_ret = slots_ret;
	mutex_unlock(&swap_slots_cache_mutex);
	return 0;
}

static void drain_slots_cache_cpu(unsigned int cpu, unsigned int type,
				  bool free_slots)
{
	struct swap_slots_cache *cache;
	swp_entry_t *slots = NULL;

	cache = &per_cpu(swp_slots, cpu);
	if ((type & SLOTS_CACHE) && cache->slots) {
		mutex_lock(&cache->alloc_lock);
		swapcache_free_entries(cache->slots + cache->cur, cache->nr);
		cache->cur = 0;
		cache->nr = 0;
		if (free_slots && cache->slots) {
			kvfree(cache->slots);
			cache->slots = NULL;
		}
		mutex_unlock(&cache->alloc_lock);
	}
	if ((type & SLOTS_CACHE_RET) && cache->slots_ret) {
		spin_lock_irq(&cache->free_lock);
		swapcache_free_entries(cache->slots_ret, cache->n_ret);
		cache->n_ret = 0;
		if (free_slots && cache->slots_ret) {
			slots = cache->slots_ret;
			cache->slots_ret = NULL;
		}
		spin_unlock_irq(&cache->free_lock);
		if (slots)
			kvfree(slots);
	}
}

static void __drain_swap_slots_cache(unsigned int type)
{
	unsigned int cpu;

	/*
	 * This function is called during
	 *	1) swapoff, when we have to make sure no
	 *	   left over slots are in cache when we remove
	 *	   a swap device;
	 *      2) disabling of swap slot cache, when we run low
	 *	   on swap slots when allocating memory and need
	 *	   to return swap slots to global pool.
	 *
	 * We cannot acquire cpu hot plug lock here as
	 * this function can be invoked in the cpu
	 * hot plug path:
	 * cpu_up -> lock cpu_hotplug -> cpu hotplug state callback
	 *   -> memory allocation -> direct reclaim -> get_swap_page
	 *   -> drain_swap_slots_cache
	 *
	 * Hence the loop over current online cpu below could miss cpu that
	 * is being brought online but not yet marked as online.
	 * That is okay as we do not schedule and run anything on a
	 * cpu before it has been marked online. Hence, we will not
	 * fill any swap slots in slots cache of such cpu.
	 * There are no slots on such cpu that need to be drained.
	 */
	for_each_online_cpu(cpu)
		drain_slots_cache_cpu(cpu, type, false);
}

static int free_slot_cache(unsigned int cpu)
{
	mutex_lock(&swap_slots_cache_mutex);
	drain_slots_cache_cpu(cpu, SLOTS_CACHE | SLOTS_CACHE_RET, true);
	mutex_unlock(&swap_slots_cache_mutex);
	return 0;
}

void enable_swap_slots_cache(void)
{
	mutex_lock(&swap_slots_cache_enable_mutex);
	if (!swap_slot_cache_initialized) {
		int ret;

		ret = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "swap_slots_cache",
					alloc_swap_slot_cache, free_slot_cache);
		if (WARN_ONCE(ret < 0, "Cache allocation failed (%s), operating "
				       "without swap slots cache.\n", __func__))
			goto out_unlock;

		swap_slot_cache_initialized = true;
	}

	__reenable_swap_slots_cache();
out_unlock:
	mutex_unlock(&swap_slots_cache_enable_mutex);
}

/* called with swap slot cache's alloc lock held */
static int refill_swap_slots_cache(struct swap_slots_cache *cache)
{
	if (!use_swap_slot_cache || cache->nr)
		return 0;

	cache->cur = 0;
	if (swap_slot_cache_active)
		cache->nr = get_swap_pages(SWAP_SLOTS_CACHE_SIZE,
					   cache->slots, 1);

	return cache->nr;
}

int free_swap_slot(swp_entry_t entry)
{
	struct swap_slots_cache *cache;

	cache = raw_cpu_ptr(&swp_slots);
	if (likely(use_swap_slot_cache && cache->slots_ret)) {
		spin_lock_irq(&cache->free_lock);
		/* Swap slots cache may be deactivated before acquiring lock */
		if (!use_swap_slot_cache || !cache->slots_ret) {
			spin_unlock_irq(&cache->free_lock);
			goto direct_free;
		}
		if (cache->n_ret >= SWAP_SLOTS_CACHE_SIZE) {
			/*
			 * Return slots to global pool.
			 * The current swap_map value is SWAP_HAS_CACHE.
			 * Set it to 0 to indicate it is available for
			 * allocation in global pool
			 */
			swapcache_free_entries(cache->slots_ret, cache->n_ret);
			cache->n_ret = 0;
		}
		cache->slots_ret[cache->n_ret++] = entry;
		spin_unlock_irq(&cache->free_lock);
	} else {
direct_free:
		swapcache_free_entries(&entry, 1);
	}

	return 0;
}

swp_entry_t get_swap_page(struct page *page)
{
	swp_entry_t entry;
	struct swap_slots_cache *cache;

	entry.val = 0;

	if (PageTransHuge(page)) {
		if (IS_ENABLED(CONFIG_THP_SWAP))
			get_swap_pages(1, &entry, HPAGE_PMD_NR);
		goto out;
	}

	/*
	 * Preemption is allowed here, because we may sleep
	 * in refill_swap_slots_cache().  But it is safe, because
	 * accesses to the per-CPU data structure are protected by the
	 * mutex cache->alloc_lock.
	 *
	 * The alloc path here does not touch cache->slots_ret
	 * so cache->free_lock is not taken.
	 */
	cache = raw_cpu_ptr(&swp_slots);

	if (likely(check_cache_active() && cache->slots)) {
		mutex_lock(&cache->alloc_lock);
		if (cache->slots) {
repeat:
			if (cache->nr) {
				entry = cache->slots[cache->cur];
				cache->slots[cache->cur++].val = 0;
				cache->nr--;
			} else if (refill_swap_slots_cache(cache)) {
				goto repeat;
			}
		}
		mutex_unlock(&cache->alloc_lock);
		if (entry.val)
			goto out;
	}

	get_swap_pages(1, &entry, 1);
out:
	if (mem_cgroup_try_charge_swap(page, entry)) {
		put_swap_page(page, entry);
		entry.val = 0;
	}
	return entry;
}
Commit	Line	Data
b2441318	1	// SPDX-License-Identifier: GPL-2.0
67afa38e TC	2	/*
	3	* Manage cache of swap slots to be used for and returned from
	4	* swap.
	5	*
	6	* Copyright(c) 2016 Intel Corporation.
	7	*
	8	* Author: Tim Chen <[email protected]>
	9	*
	10	* We allocate the swap slots from the global pool and put
	11	* it into local per cpu caches. This has the advantage
	12	* of no needing to acquire the swap_info lock every time
	13	* we need a new slot.
	14	*
	15	* There is also opportunity to simply return the slot
	16	* to local caches without needing to acquire swap_info
	17	* lock. We do not reuse the returned slots directly but
	18	* move them back to the global pool in a batch. This
	19	* allows the slots to coaellesce and reduce fragmentation.
	20	*
	21	* The swap entry allocated is marked with SWAP_HAS_CACHE
	22	* flag in map_count that prevents it from being allocated
	23	* again from the global pool.
	24	*
	25	* The swap slots cache is protected by a mutex instead of
	26	* a spin lock as when we search for slots with scan_swap_map,
	27	* we can possibly sleep.
	28	*/
	29
	30	#include <linux/swap_slots.h>
	31	#include <linux/cpu.h>
	32	#include <linux/cpumask.h>
	33	#include <linux/vmalloc.h>
	34	#include <linux/mutex.h>
54f180d3	35	#include <linux/mm.h>
67afa38e	36
67afa38e TC	37	static DEFINE_PER_CPU(struct swap_slots_cache, swp_slots);
67afa38e TC	38	static bool swap_slot_cache_active;
ba81f838	39	bool swap_slot_cache_enabled;
67afa38e	40	static bool swap_slot_cache_initialized;
31f21da1	41	static DEFINE_MUTEX(swap_slots_cache_mutex);
67afa38e	42	/* Serialize swap slots cache enable/disable operations */
31f21da1	43	static DEFINE_MUTEX(swap_slots_cache_enable_mutex);
67afa38e TC	44
	45	static void __drain_swap_slots_cache(unsigned int type);
	46	static void deactivate_swap_slots_cache(void);
	47	static void reactivate_swap_slots_cache(void);
	48
e0f3ebba	49	#define use_swap_slot_cache (swap_slot_cache_active && swap_slot_cache_enabled)
67afa38e TC	50	#define SLOTS_CACHE 0x1
	51	#define SLOTS_CACHE_RET 0x2
	52
	53	static void deactivate_swap_slots_cache(void)
	54	{
	55	mutex_lock(&swap_slots_cache_mutex);
	56	swap_slot_cache_active = false;
	57	__drain_swap_slots_cache(SLOTS_CACHE\|SLOTS_CACHE_RET);
	58	mutex_unlock(&swap_slots_cache_mutex);
	59	}
	60
	61	static void reactivate_swap_slots_cache(void)
	62	{
	63	mutex_lock(&swap_slots_cache_mutex);
	64	swap_slot_cache_active = true;
	65	mutex_unlock(&swap_slots_cache_mutex);
	66	}
	67
	68	/* Must not be called with cpu hot plug lock */
	69	void disable_swap_slots_cache_lock(void)
	70	{
	71	mutex_lock(&swap_slots_cache_enable_mutex);
	72	swap_slot_cache_enabled = false;
	73	if (swap_slot_cache_initialized) {
	74	/* serialize with cpu hotplug operations */
	75	get_online_cpus();
	76	__drain_swap_slots_cache(SLOTS_CACHE\|SLOTS_CACHE_RET);
	77	put_online_cpus();
	78	}
	79	}
	80
	81	static void __reenable_swap_slots_cache(void)
	82	{
	83	swap_slot_cache_enabled = has_usable_swap();
	84	}
	85
	86	void reenable_swap_slots_cache_unlock(void)
	87	{
	88	__reenable_swap_slots_cache();
	89	mutex_unlock(&swap_slots_cache_enable_mutex);
	90	}
	91
	92	static bool check_cache_active(void)
	93	{
	94	long pages;
	95
e0f3ebba	96	if (!swap_slot_cache_enabled)
67afa38e TC	97	return false;
	98
	99	pages = get_nr_swap_pages();
	100	if (!swap_slot_cache_active) {
	101	if (pages > num_online_cpus() *
	102	THRESHOLD_ACTIVATE_SWAP_SLOTS_CACHE)
	103	reactivate_swap_slots_cache();
	104	goto out;
	105	}
	106
	107	/* if global pool of slot caches too low, deactivate cache */
	108	if (pages < num_online_cpus() * THRESHOLD_DEACTIVATE_SWAP_SLOTS_CACHE)
	109	deactivate_swap_slots_cache();
	110	out:
	111	return swap_slot_cache_active;
	112	}
	113
	114	static int alloc_swap_slot_cache(unsigned int cpu)
	115	{
	116	struct swap_slots_cache *cache;
	117	swp_entry_t slots, slots_ret;
	118
	119	/*
	120	* Do allocation outside swap_slots_cache_mutex
54f180d3	121	* as kvzalloc could trigger reclaim and get_swap_page,
67afa38e TC	122	* which can lock swap_slots_cache_mutex.
67afa38e TC	123	*/
778e1cdd	124	slots = kvcalloc(SWAP_SLOTS_CACHE_SIZE, sizeof(swp_entry_t),
54f180d3	125	GFP_KERNEL);
67afa38e TC	126	if (!slots)
	127	return -ENOMEM;
	128
778e1cdd	129	slots_ret = kvcalloc(SWAP_SLOTS_CACHE_SIZE, sizeof(swp_entry_t),
54f180d3	130	GFP_KERNEL);
67afa38e	131	if (!slots_ret) {
54f180d3	132	kvfree(slots);
67afa38e TC	133	return -ENOMEM;
	134	}
	135
	136	mutex_lock(&swap_slots_cache_mutex);
	137	cache = &per_cpu(swp_slots, cpu);
f90eae2a	138	if (cache->slots \|\| cache->slots_ret) {
67afa38e	139	/* cache already allocated */
f90eae2a ZL	140	mutex_unlock(&swap_slots_cache_mutex);
	141
	142	kvfree(slots);
	143	kvfree(slots_ret);
	144
	145	return 0;
	146	}
	147
67afa38e TC	148	if (!cache->lock_initialized) {
	149	mutex_init(&cache->alloc_lock);
	150	spin_lock_init(&cache->free_lock);
	151	cache->lock_initialized = true;
	152	}
	153	cache->nr = 0;
	154	cache->cur = 0;
	155	cache->n_ret = 0;
a2e16731 TC	156	/*
	157	* We initialized alloc_lock and free_lock earlier. We use
	158	* !cache->slots or !cache->slots_ret to know if it is safe to acquire
	159	* the corresponding lock and use the cache. Memory barrier below
	160	* ensures the assumption.
	161	*/
	162	mb();
67afa38e	163	cache->slots = slots;
67afa38e	164	cache->slots_ret = slots_ret;
67afa38e	165	mutex_unlock(&swap_slots_cache_mutex);
67afa38e TC	166	return 0;
	167	}
	168
	169	static void drain_slots_cache_cpu(unsigned int cpu, unsigned int type,
	170	bool free_slots)
	171	{
	172	struct swap_slots_cache *cache;
	173	swp_entry_t *slots = NULL;
	174
	175	cache = &per_cpu(swp_slots, cpu);
	176	if ((type & SLOTS_CACHE) && cache->slots) {
	177	mutex_lock(&cache->alloc_lock);
	178	swapcache_free_entries(cache->slots + cache->cur, cache->nr);
	179	cache->cur = 0;
	180	cache->nr = 0;
	181	if (free_slots && cache->slots) {
54f180d3	182	kvfree(cache->slots);
67afa38e TC	183	cache->slots = NULL;
	184	}
	185	mutex_unlock(&cache->alloc_lock);
	186	}
	187	if ((type & SLOTS_CACHE_RET) && cache->slots_ret) {
	188	spin_lock_irq(&cache->free_lock);
	189	swapcache_free_entries(cache->slots_ret, cache->n_ret);
	190	cache->n_ret = 0;
	191	if (free_slots && cache->slots_ret) {
	192	slots = cache->slots_ret;
	193	cache->slots_ret = NULL;
	194	}
	195	spin_unlock_irq(&cache->free_lock);
	196	if (slots)
54f180d3	197	kvfree(slots);
67afa38e TC	198	}
	199	}
	200
	201	static void __drain_swap_slots_cache(unsigned int type)
	202	{
	203	unsigned int cpu;
	204
	205	/*
	206	* This function is called during
	207	* 1) swapoff, when we have to make sure no
	208	* left over slots are in cache when we remove
	209	* a swap device;
	210	* 2) disabling of swap slot cache, when we run low
	211	* on swap slots when allocating memory and need
	212	* to return swap slots to global pool.
	213	*
	214	* We cannot acquire cpu hot plug lock here as
	215	* this function can be invoked in the cpu
	216	* hot plug path:
	217	* cpu_up -> lock cpu_hotplug -> cpu hotplug state callback
	218	* -> memory allocation -> direct reclaim -> get_swap_page
	219	* -> drain_swap_slots_cache
	220	*
	221	* Hence the loop over current online cpu below could miss cpu that
	222	* is being brought online but not yet marked as online.
	223	* That is okay as we do not schedule and run anything on a
	224	* cpu before it has been marked online. Hence, we will not
	225	* fill any swap slots in slots cache of such cpu.
	226	* There are no slots on such cpu that need to be drained.
	227	*/
	228	for_each_online_cpu(cpu)
	229	drain_slots_cache_cpu(cpu, type, false);
	230	}
	231
	232	static int free_slot_cache(unsigned int cpu)
	233	{
	234	mutex_lock(&swap_slots_cache_mutex);
	235	drain_slots_cache_cpu(cpu, SLOTS_CACHE \| SLOTS_CACHE_RET, true);
	236	mutex_unlock(&swap_slots_cache_mutex);
	237	return 0;
	238	}
	239
f3bc52cb	240	void enable_swap_slots_cache(void)
67afa38e	241	{
67afa38e	242	mutex_lock(&swap_slots_cache_enable_mutex);
d69a9575 ZL	243	if (!swap_slot_cache_initialized) {
d69a9575 ZL	244	int ret;
67afa38e	245
d69a9575 ZL	246	ret = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "swap_slots_cache",
	247	alloc_swap_slot_cache, free_slot_cache);
	248	if (WARN_ONCE(ret < 0, "Cache allocation failed (%s), operating "
	249	"without swap slots cache.\n", __func__))
	250	goto out_unlock;
	251
	252	swap_slot_cache_initialized = true;
	253	}
9b7a8143	254
67afa38e TC	255	__reenable_swap_slots_cache();
	256	out_unlock:
	257	mutex_unlock(&swap_slots_cache_enable_mutex);
67afa38e TC	258	}
	259
	260	/* called with swap slot cache's alloc lock held */
	261	static int refill_swap_slots_cache(struct swap_slots_cache *cache)
	262	{
	263	if (!use_swap_slot_cache \|\| cache->nr)
	264	return 0;
	265
	266	cache->cur = 0;
	267	if (swap_slot_cache_active)
5d5e8f19 YH	268	cache->nr = get_swap_pages(SWAP_SLOTS_CACHE_SIZE,
5d5e8f19 YH	269	cache->slots, 1);
67afa38e TC	270
	271	return cache->nr;
	272	}
	273
	274	int free_swap_slot(swp_entry_t entry)
	275	{
	276	struct swap_slots_cache *cache;
	277
f07e0f84	278	cache = raw_cpu_ptr(&swp_slots);
a2e16731	279	if (likely(use_swap_slot_cache && cache->slots_ret)) {
67afa38e TC	280	spin_lock_irq(&cache->free_lock);
67afa38e TC	281	/* Swap slots cache may be deactivated before acquiring lock */
f07e0f84	282	if (!use_swap_slot_cache \|\| !cache->slots_ret) {
67afa38e TC	283	spin_unlock_irq(&cache->free_lock);
	284	goto direct_free;
	285	}
	286	if (cache->n_ret >= SWAP_SLOTS_CACHE_SIZE) {
	287	/*
	288	* Return slots to global pool.
	289	* The current swap_map value is SWAP_HAS_CACHE.
	290	* Set it to 0 to indicate it is available for
	291	* allocation in global pool
	292	*/
	293	swapcache_free_entries(cache->slots_ret, cache->n_ret);
	294	cache->n_ret = 0;
	295	}
	296	cache->slots_ret[cache->n_ret++] = entry;
	297	spin_unlock_irq(&cache->free_lock);
	298	} else {
	299	direct_free:
	300	swapcache_free_entries(&entry, 1);
	301	}
67afa38e TC	302
	303	return 0;
	304	}
	305
38d8b4e6	306	swp_entry_t get_swap_page(struct page *page)
67afa38e	307	{
2406b76f	308	swp_entry_t entry;
67afa38e TC	309	struct swap_slots_cache *cache;
67afa38e TC	310
38d8b4e6 YH	311	entry.val = 0;
	312
	313	if (PageTransHuge(page)) {
	314	if (IS_ENABLED(CONFIG_THP_SWAP))
5d5e8f19	315	get_swap_pages(1, &entry, HPAGE_PMD_NR);
bb98f2c5	316	goto out;
38d8b4e6 YH	317	}
38d8b4e6 YH	318
67afa38e TC	319	/*
	320	* Preemption is allowed here, because we may sleep
	321	* in refill_swap_slots_cache(). But it is safe, because
	322	* accesses to the per-CPU data structure are protected by the
	323	* mutex cache->alloc_lock.
	324	*
	325	* The alloc path here does not touch cache->slots_ret
	326	* so cache->free_lock is not taken.
	327	*/
	328	cache = raw_cpu_ptr(&swp_slots);
	329
a2e16731	330	if (likely(check_cache_active() && cache->slots)) {
67afa38e TC	331	mutex_lock(&cache->alloc_lock);
	332	if (cache->slots) {
	333	repeat:
	334	if (cache->nr) {
2406b76f WY	335	entry = cache->slots[cache->cur];
2406b76f WY	336	cache->slots[cache->cur++].val = 0;
67afa38e	337	cache->nr--;
2406b76f WY	338	} else if (refill_swap_slots_cache(cache)) {
2406b76f WY	339	goto repeat;
67afa38e TC	340	}
	341	}
	342	mutex_unlock(&cache->alloc_lock);
	343	if (entry.val)
bb98f2c5	344	goto out;
67afa38e TC	345	}
67afa38e TC	346
5d5e8f19	347	get_swap_pages(1, &entry, 1);
bb98f2c5 TH	348	out:
	349	if (mem_cgroup_try_charge_swap(page, entry)) {
	350	put_swap_page(page, entry);
	351	entry.val = 0;
	352	}
67afa38e TC	353	return entry;
67afa38e TC	354	}