[mirror_ubuntu-bionic-kernel.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 <tim.c.chen@linux.intel.com>
 *
 * 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>

#ifdef CONFIG_SWAP

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;
DEFINE_MUTEX(swap_slots_cache_mutex);
/* Serialize swap slots cache enable/disable operations */
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 && swap_slot_cache_initialized)
#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 || !swap_slot_cache_initialized)
		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 = kvzalloc(sizeof(swp_entry_t) * SWAP_SLOTS_CACHE_SIZE,
			 GFP_KERNEL);
	if (!slots)
		return -ENOMEM;

	slots_ret = kvzalloc(sizeof(swp_entry_t) * SWAP_SLOTS_CACHE_SIZE,
			     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 */
		goto out;
	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;
	slots = NULL;
	cache->slots_ret = slots_ret;
	slots_ret = NULL;
out:
	mutex_unlock(&swap_slots_cache_mutex);
	if (slots)
		kvfree(slots);
	if (slots_ret)
		kvfree(slots_ret);
	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;
}

int enable_swap_slots_cache(void)
{
	int ret = 0;

	mutex_lock(&swap_slots_cache_enable_mutex);
	if (swap_slot_cache_initialized) {
		__reenable_swap_slots_cache();
		goto out_unlock;
	}

	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);
	return 0;
}

/* 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, false,
					   cache->slots);

	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, *pentry;
	struct swap_slots_cache *cache;

	entry.val = 0;

	if (PageTransHuge(page)) {
		if (IS_ENABLED(CONFIG_THP_SWAP))
			get_swap_pages(1, true, &entry);
		return entry;
	}

	/*
	 * 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) {
				pentry = &cache->slots[cache->cur++];
				entry = *pentry;
				pentry->val = 0;
				cache->nr--;
			} else {
				if (refill_swap_slots_cache(cache))
					goto repeat;
			}
		}
		mutex_unlock(&cache->alloc_lock);
		if (entry.val)
			return entry;
	}

	get_swap_pages(1, false, &entry);

	return entry;
}

#endif /* CONFIG_SWAP */
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 <tim.c.chen@linux.intel.com>
	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 TC	36
	37	#ifdef CONFIG_SWAP
	38
	39	static DEFINE_PER_CPU(struct swap_slots_cache, swp_slots);
	40	static bool swap_slot_cache_active;
ba81f838	41	bool swap_slot_cache_enabled;
67afa38e TC	42	static bool swap_slot_cache_initialized;
	43	DEFINE_MUTEX(swap_slots_cache_mutex);
	44	/* Serialize swap slots cache enable/disable operations */
	45	DEFINE_MUTEX(swap_slots_cache_enable_mutex);
	46
	47	static void __drain_swap_slots_cache(unsigned int type);
	48	static void deactivate_swap_slots_cache(void);
	49	static void reactivate_swap_slots_cache(void);
	50
	51	#define use_swap_slot_cache (swap_slot_cache_active && \
	52	swap_slot_cache_enabled && swap_slot_cache_initialized)
	53	#define SLOTS_CACHE 0x1
	54	#define SLOTS_CACHE_RET 0x2
	55
	56	static void deactivate_swap_slots_cache(void)
	57	{
	58	mutex_lock(&swap_slots_cache_mutex);
	59	swap_slot_cache_active = false;
	60	__drain_swap_slots_cache(SLOTS_CACHE\|SLOTS_CACHE_RET);
	61	mutex_unlock(&swap_slots_cache_mutex);
	62	}
	63
	64	static void reactivate_swap_slots_cache(void)
	65	{
	66	mutex_lock(&swap_slots_cache_mutex);
	67	swap_slot_cache_active = true;
	68	mutex_unlock(&swap_slots_cache_mutex);
	69	}
	70
	71	/* Must not be called with cpu hot plug lock */
	72	void disable_swap_slots_cache_lock(void)
	73	{
	74	mutex_lock(&swap_slots_cache_enable_mutex);
	75	swap_slot_cache_enabled = false;
	76	if (swap_slot_cache_initialized) {
	77	/* serialize with cpu hotplug operations */
	78	get_online_cpus();
	79	__drain_swap_slots_cache(SLOTS_CACHE\|SLOTS_CACHE_RET);
	80	put_online_cpus();
	81	}
	82	}
	83
	84	static void __reenable_swap_slots_cache(void)
	85	{
	86	swap_slot_cache_enabled = has_usable_swap();
	87	}
	88
	89	void reenable_swap_slots_cache_unlock(void)
	90	{
	91	__reenable_swap_slots_cache();
	92	mutex_unlock(&swap_slots_cache_enable_mutex);
	93	}
	94
	95	static bool check_cache_active(void)
	96	{
	97	long pages;
	98
	99	if (!swap_slot_cache_enabled \|\| !swap_slot_cache_initialized)
	100	return false;
	101
	102	pages = get_nr_swap_pages();
	103	if (!swap_slot_cache_active) {
	104	if (pages > num_online_cpus() *
	105	THRESHOLD_ACTIVATE_SWAP_SLOTS_CACHE)
106	reactivate_swap_slots_cache();
107	goto out;
108	}
109
110	/* if global pool of slot caches too low, deactivate cache */
111	if (pages < num_online_cpus() * THRESHOLD_DEACTIVATE_SWAP_SLOTS_CACHE)
112	deactivate_swap_slots_cache();
113	out:
114	return swap_slot_cache_active;
115	}
116
117	static int alloc_swap_slot_cache(unsigned int cpu)
118	{
119	struct swap_slots_cache *cache;
120	swp_entry_t slots, slots_ret;
121
122	/*
123	* Do allocation outside swap_slots_cache_mutex
54f180d3	124	* as kvzalloc could trigger reclaim and get_swap_page,
67afa38e TC	125	* which can lock swap_slots_cache_mutex.
67afa38e TC	126	*/
54f180d3 HY	127	slots = kvzalloc(sizeof(swp_entry_t) * SWAP_SLOTS_CACHE_SIZE,
54f180d3 HY	128	GFP_KERNEL);
67afa38e TC	129	if (!slots)
	130	return -ENOMEM;
	131
54f180d3 HY	132	slots_ret = kvzalloc(sizeof(swp_entry_t) * SWAP_SLOTS_CACHE_SIZE,
54f180d3 HY	133	GFP_KERNEL);
67afa38e	134	if (!slots_ret) {
54f180d3	135	kvfree(slots);
67afa38e TC	136	return -ENOMEM;
	137	}
	138
	139	mutex_lock(&swap_slots_cache_mutex);
	140	cache = &per_cpu(swp_slots, cpu);
	141	if (cache->slots \|\| cache->slots_ret)
	142	/* cache already allocated */
	143	goto out;
	144	if (!cache->lock_initialized) {
	145	mutex_init(&cache->alloc_lock);
	146	spin_lock_init(&cache->free_lock);
	147	cache->lock_initialized = true;
	148	}
	149	cache->nr = 0;
	150	cache->cur = 0;
	151	cache->n_ret = 0;
a2e16731 TC	152	/*
	153	* We initialized alloc_lock and free_lock earlier. We use
	154	* !cache->slots or !cache->slots_ret to know if it is safe to acquire
	155	* the corresponding lock and use the cache. Memory barrier below
	156	* ensures the assumption.
	157	*/
	158	mb();
67afa38e TC	159	cache->slots = slots;
	160	slots = NULL;
	161	cache->slots_ret = slots_ret;
	162	slots_ret = NULL;
	163	out:
	164	mutex_unlock(&swap_slots_cache_mutex);
	165	if (slots)
54f180d3	166	kvfree(slots);
67afa38e	167	if (slots_ret)
54f180d3	168	kvfree(slots_ret);
67afa38e TC	169	return 0;
	170	}
	171
	172	static void drain_slots_cache_cpu(unsigned int cpu, unsigned int type,
	173	bool free_slots)
	174	{
	175	struct swap_slots_cache *cache;
	176	swp_entry_t *slots = NULL;
	177
	178	cache = &per_cpu(swp_slots, cpu);
	179	if ((type & SLOTS_CACHE) && cache->slots) {
	180	mutex_lock(&cache->alloc_lock);
	181	swapcache_free_entries(cache->slots + cache->cur, cache->nr);
	182	cache->cur = 0;
	183	cache->nr = 0;
	184	if (free_slots && cache->slots) {
54f180d3	185	kvfree(cache->slots);
67afa38e TC	186	cache->slots = NULL;
	187	}
	188	mutex_unlock(&cache->alloc_lock);
	189	}
	190	if ((type & SLOTS_CACHE_RET) && cache->slots_ret) {
	191	spin_lock_irq(&cache->free_lock);
	192	swapcache_free_entries(cache->slots_ret, cache->n_ret);
	193	cache->n_ret = 0;
	194	if (free_slots && cache->slots_ret) {
	195	slots = cache->slots_ret;
	196	cache->slots_ret = NULL;
	197	}
	198	spin_unlock_irq(&cache->free_lock);
	199	if (slots)
54f180d3	200	kvfree(slots);
67afa38e TC	201	}
	202	}
	203
	204	static void __drain_swap_slots_cache(unsigned int type)
	205	{
	206	unsigned int cpu;
	207
	208	/*
	209	* This function is called during
	210	* 1) swapoff, when we have to make sure no
	211	* left over slots are in cache when we remove
	212	* a swap device;
	213	* 2) disabling of swap slot cache, when we run low
	214	* on swap slots when allocating memory and need
	215	* to return swap slots to global pool.
	216	*
	217	* We cannot acquire cpu hot plug lock here as
	218	* this function can be invoked in the cpu
	219	* hot plug path:
	220	* cpu_up -> lock cpu_hotplug -> cpu hotplug state callback
	221	* -> memory allocation -> direct reclaim -> get_swap_page
	222	* -> drain_swap_slots_cache
	223	*
	224	* Hence the loop over current online cpu below could miss cpu that
	225	* is being brought online but not yet marked as online.
	226	* That is okay as we do not schedule and run anything on a
	227	* cpu before it has been marked online. Hence, we will not
	228	* fill any swap slots in slots cache of such cpu.
	229	* There are no slots on such cpu that need to be drained.
	230	*/
	231	for_each_online_cpu(cpu)
	232	drain_slots_cache_cpu(cpu, type, false);
	233	}
	234
	235	static int free_slot_cache(unsigned int cpu)
	236	{
	237	mutex_lock(&swap_slots_cache_mutex);
	238	drain_slots_cache_cpu(cpu, SLOTS_CACHE \| SLOTS_CACHE_RET, true);
	239	mutex_unlock(&swap_slots_cache_mutex);
	240	return 0;
	241	}
	242
	243	int enable_swap_slots_cache(void)
	244	{
	245	int ret = 0;
	246
	247	mutex_lock(&swap_slots_cache_enable_mutex);
	248	if (swap_slot_cache_initialized) {
	249	__reenable_swap_slots_cache();
	250	goto out_unlock;
	251	}
	252
	253	ret = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "swap_slots_cache",
	254	alloc_swap_slot_cache, free_slot_cache);
9b7a8143 TC	255	if (WARN_ONCE(ret < 0, "Cache allocation failed (%s), operating "
9b7a8143 TC	256	"without swap slots cache.\n", __func__))
67afa38e	257	goto out_unlock;
9b7a8143	258
67afa38e TC	259	swap_slot_cache_initialized = true;
	260	__reenable_swap_slots_cache();
	261	out_unlock:
	262	mutex_unlock(&swap_slots_cache_enable_mutex);
	263	return 0;
	264	}
	265
	266	/* called with swap slot cache's alloc lock held */
	267	static int refill_swap_slots_cache(struct swap_slots_cache *cache)
	268	{
	269	if (!use_swap_slot_cache \|\| cache->nr)
	270	return 0;
	271
	272	cache->cur = 0;
	273	if (swap_slot_cache_active)
38d8b4e6 HY	274	cache->nr = get_swap_pages(SWAP_SLOTS_CACHE_SIZE, false,
38d8b4e6 HY	275	cache->slots);
67afa38e TC	276
	277	return cache->nr;
	278	}
	279
	280	int free_swap_slot(swp_entry_t entry)
	281	{
	282	struct swap_slots_cache *cache;
	283
f07e0f84	284	cache = raw_cpu_ptr(&swp_slots);
a2e16731	285	if (likely(use_swap_slot_cache && cache->slots_ret)) {
67afa38e TC	286	spin_lock_irq(&cache->free_lock);
67afa38e TC	287	/* Swap slots cache may be deactivated before acquiring lock */
f07e0f84	288	if (!use_swap_slot_cache \|\| !cache->slots_ret) {
67afa38e TC	289	spin_unlock_irq(&cache->free_lock);
	290	goto direct_free;
	291	}
	292	if (cache->n_ret >= SWAP_SLOTS_CACHE_SIZE) {
	293	/*
	294	* Return slots to global pool.
	295	* The current swap_map value is SWAP_HAS_CACHE.
	296	* Set it to 0 to indicate it is available for
	297	* allocation in global pool
	298	*/
	299	swapcache_free_entries(cache->slots_ret, cache->n_ret);
	300	cache->n_ret = 0;
	301	}
	302	cache->slots_ret[cache->n_ret++] = entry;
	303	spin_unlock_irq(&cache->free_lock);
	304	} else {
	305	direct_free:
	306	swapcache_free_entries(&entry, 1);
	307	}
67afa38e TC	308
	309	return 0;
	310	}
	311
38d8b4e6	312	swp_entry_t get_swap_page(struct page *page)
67afa38e TC	313	{
	314	swp_entry_t entry, *pentry;
	315	struct swap_slots_cache *cache;
	316
38d8b4e6 HY	317	entry.val = 0;
	318
	319	if (PageTransHuge(page)) {
	320	if (IS_ENABLED(CONFIG_THP_SWAP))
	321	get_swap_pages(1, true, &entry);
	322	return entry;
	323	}
	324
67afa38e TC	325	/*
	326	* Preemption is allowed here, because we may sleep
	327	* in refill_swap_slots_cache(). But it is safe, because
	328	* accesses to the per-CPU data structure are protected by the
	329	* mutex cache->alloc_lock.
	330	*
	331	* The alloc path here does not touch cache->slots_ret
	332	* so cache->free_lock is not taken.
	333	*/
	334	cache = raw_cpu_ptr(&swp_slots);
	335
a2e16731	336	if (likely(check_cache_active() && cache->slots)) {
67afa38e TC	337	mutex_lock(&cache->alloc_lock);
	338	if (cache->slots) {
	339	repeat:
	340	if (cache->nr) {
	341	pentry = &cache->slots[cache->cur++];
	342	entry = *pentry;
	343	pentry->val = 0;
	344	cache->nr--;
	345	} else {
	346	if (refill_swap_slots_cache(cache))
	347	goto repeat;
	348	}
	349	}
	350	mutex_unlock(&cache->alloc_lock);
	351	if (entry.val)
	352	return entry;
	353	}
	354
38d8b4e6	355	get_swap_pages(1, false, &entry);
67afa38e TC	356
	357	return entry;
	358	}
	359
	360	#endif /* CONFIG_SWAP */