[mirror_ubuntu-jammy-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 coalesce 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);

#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 */
		cpus_read_lock();
		__drain_swap_slots_cache(SLOTS_CACHE|SLOTS_CACHE_RET);
		cpus_read_unlock();
	}
}

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);
		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 <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
f0953a1b	19	* allows the slots to coalesce and reduce fragmentation.
67afa38e TC	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
67afa38e TC	45	static void __drain_swap_slots_cache(unsigned int type);
67afa38e	46
e0f3ebba	47	#define use_swap_slot_cache (swap_slot_cache_active && swap_slot_cache_enabled)
67afa38e TC	48	#define SLOTS_CACHE 0x1
	49	#define SLOTS_CACHE_RET 0x2
	50
	51	static void deactivate_swap_slots_cache(void)
	52	{
	53	mutex_lock(&swap_slots_cache_mutex);
	54	swap_slot_cache_active = false;
	55	__drain_swap_slots_cache(SLOTS_CACHE\|SLOTS_CACHE_RET);
	56	mutex_unlock(&swap_slots_cache_mutex);
	57	}
	58
	59	static void reactivate_swap_slots_cache(void)
	60	{
	61	mutex_lock(&swap_slots_cache_mutex);
	62	swap_slot_cache_active = true;
	63	mutex_unlock(&swap_slots_cache_mutex);
	64	}
	65
	66	/* Must not be called with cpu hot plug lock */
	67	void disable_swap_slots_cache_lock(void)
	68	{
	69	mutex_lock(&swap_slots_cache_enable_mutex);
	70	swap_slot_cache_enabled = false;
	71	if (swap_slot_cache_initialized) {
	72	/* serialize with cpu hotplug operations */
7625eccd	73	cpus_read_lock();
67afa38e	74	__drain_swap_slots_cache(SLOTS_CACHE\|SLOTS_CACHE_RET);
7625eccd	75	cpus_read_unlock();
67afa38e TC	76	}
	77	}
	78
	79	static void __reenable_swap_slots_cache(void)
	80	{
	81	swap_slot_cache_enabled = has_usable_swap();
	82	}
	83
	84	void reenable_swap_slots_cache_unlock(void)
	85	{
	86	__reenable_swap_slots_cache();
	87	mutex_unlock(&swap_slots_cache_enable_mutex);
	88	}
	89
	90	static bool check_cache_active(void)
	91	{
	92	long pages;
	93
e0f3ebba	94	if (!swap_slot_cache_enabled)
67afa38e TC	95	return false;
	96
	97	pages = get_nr_swap_pages();
	98	if (!swap_slot_cache_active) {
	99	if (pages > num_online_cpus() *
	100	THRESHOLD_ACTIVATE_SWAP_SLOTS_CACHE)
	101	reactivate_swap_slots_cache();
	102	goto out;
	103	}
	104
	105	/* if global pool of slot caches too low, deactivate cache */
	106	if (pages < num_online_cpus() * THRESHOLD_DEACTIVATE_SWAP_SLOTS_CACHE)
	107	deactivate_swap_slots_cache();
	108	out:
	109	return swap_slot_cache_active;
	110	}
	111
	112	static int alloc_swap_slot_cache(unsigned int cpu)
	113	{
	114	struct swap_slots_cache *cache;
	115	swp_entry_t slots, slots_ret;
	116
	117	/*
	118	* Do allocation outside swap_slots_cache_mutex
54f180d3	119	* as kvzalloc could trigger reclaim and get_swap_page,
67afa38e TC	120	* which can lock swap_slots_cache_mutex.
67afa38e TC	121	*/
778e1cdd	122	slots = kvcalloc(SWAP_SLOTS_CACHE_SIZE, sizeof(swp_entry_t),
54f180d3	123	GFP_KERNEL);
67afa38e TC	124	if (!slots)
	125	return -ENOMEM;
	126
778e1cdd	127	slots_ret = kvcalloc(SWAP_SLOTS_CACHE_SIZE, sizeof(swp_entry_t),
54f180d3	128	GFP_KERNEL);
67afa38e	129	if (!slots_ret) {
54f180d3	130	kvfree(slots);
67afa38e TC	131	return -ENOMEM;
	132	}
	133
	134	mutex_lock(&swap_slots_cache_mutex);
	135	cache = &per_cpu(swp_slots, cpu);
f90eae2a	136	if (cache->slots \|\| cache->slots_ret) {
67afa38e	137	/* cache already allocated */
f90eae2a ZL	138	mutex_unlock(&swap_slots_cache_mutex);
	139
	140	kvfree(slots);
	141	kvfree(slots_ret);
	142
	143	return 0;
	144	}
	145
67afa38e TC	146	if (!cache->lock_initialized) {
	147	mutex_init(&cache->alloc_lock);
	148	spin_lock_init(&cache->free_lock);
	149	cache->lock_initialized = true;
	150	}
	151	cache->nr = 0;
	152	cache->cur = 0;
	153	cache->n_ret = 0;
a2e16731 TC	154	/*
	155	* We initialized alloc_lock and free_lock earlier. We use
	156	* !cache->slots or !cache->slots_ret to know if it is safe to acquire
	157	* the corresponding lock and use the cache. Memory barrier below
	158	* ensures the assumption.
	159	*/
	160	mb();
67afa38e	161	cache->slots = slots;
67afa38e	162	cache->slots_ret = slots_ret;
67afa38e	163	mutex_unlock(&swap_slots_cache_mutex);
67afa38e TC	164	return 0;
	165	}
	166
	167	static void drain_slots_cache_cpu(unsigned int cpu, unsigned int type,
	168	bool free_slots)
	169	{
	170	struct swap_slots_cache *cache;
	171	swp_entry_t *slots = NULL;
	172
	173	cache = &per_cpu(swp_slots, cpu);
	174	if ((type & SLOTS_CACHE) && cache->slots) {
	175	mutex_lock(&cache->alloc_lock);
	176	swapcache_free_entries(cache->slots + cache->cur, cache->nr);
	177	cache->cur = 0;
	178	cache->nr = 0;
	179	if (free_slots && cache->slots) {
54f180d3	180	kvfree(cache->slots);
67afa38e TC	181	cache->slots = NULL;
	182	}
	183	mutex_unlock(&cache->alloc_lock);
	184	}
	185	if ((type & SLOTS_CACHE_RET) && cache->slots_ret) {
	186	spin_lock_irq(&cache->free_lock);
	187	swapcache_free_entries(cache->slots_ret, cache->n_ret);
	188	cache->n_ret = 0;
	189	if (free_slots && cache->slots_ret) {
	190	slots = cache->slots_ret;
	191	cache->slots_ret = NULL;
	192	}
	193	spin_unlock_irq(&cache->free_lock);
191a7221	194	kvfree(slots);
67afa38e TC	195	}
	196	}
	197
	198	static void __drain_swap_slots_cache(unsigned int type)
	199	{
	200	unsigned int cpu;
	201
	202	/*
	203	* This function is called during
	204	* 1) swapoff, when we have to make sure no
	205	* left over slots are in cache when we remove
	206	* a swap device;
	207	* 2) disabling of swap slot cache, when we run low
	208	* on swap slots when allocating memory and need
	209	* to return swap slots to global pool.
	210	*
	211	* We cannot acquire cpu hot plug lock here as
	212	* this function can be invoked in the cpu
	213	* hot plug path:
	214	* cpu_up -> lock cpu_hotplug -> cpu hotplug state callback
	215	* -> memory allocation -> direct reclaim -> get_swap_page
	216	* -> drain_swap_slots_cache
	217	*
	218	* Hence the loop over current online cpu below could miss cpu that
	219	* is being brought online but not yet marked as online.
	220	* That is okay as we do not schedule and run anything on a
	221	* cpu before it has been marked online. Hence, we will not
	222	* fill any swap slots in slots cache of such cpu.
	223	* There are no slots on such cpu that need to be drained.
	224	*/
	225	for_each_online_cpu(cpu)
	226	drain_slots_cache_cpu(cpu, type, false);
	227	}
	228
	229	static int free_slot_cache(unsigned int cpu)
	230	{
	231	mutex_lock(&swap_slots_cache_mutex);
	232	drain_slots_cache_cpu(cpu, SLOTS_CACHE \| SLOTS_CACHE_RET, true);
	233	mutex_unlock(&swap_slots_cache_mutex);
	234	return 0;
	235	}
	236
f3bc52cb	237	void enable_swap_slots_cache(void)
67afa38e	238	{
67afa38e	239	mutex_lock(&swap_slots_cache_enable_mutex);
d69a9575 ZL	240	if (!swap_slot_cache_initialized) {
d69a9575 ZL	241	int ret;
67afa38e	242
d69a9575 ZL	243	ret = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "swap_slots_cache",
	244	alloc_swap_slot_cache, free_slot_cache);
	245	if (WARN_ONCE(ret < 0, "Cache allocation failed (%s), operating "
	246	"without swap slots cache.\n", __func__))
	247	goto out_unlock;
	248
	249	swap_slot_cache_initialized = true;
	250	}
9b7a8143	251
67afa38e TC	252	__reenable_swap_slots_cache();
	253	out_unlock:
	254	mutex_unlock(&swap_slots_cache_enable_mutex);
67afa38e TC	255	}
	256
	257	/* called with swap slot cache's alloc lock held */
	258	static int refill_swap_slots_cache(struct swap_slots_cache *cache)
	259	{
	260	if (!use_swap_slot_cache \|\| cache->nr)
	261	return 0;
	262
	263	cache->cur = 0;
	264	if (swap_slot_cache_active)
5d5e8f19 HY	265	cache->nr = get_swap_pages(SWAP_SLOTS_CACHE_SIZE,
5d5e8f19 HY	266	cache->slots, 1);
67afa38e TC	267
	268	return cache->nr;
	269	}
	270
	271	int free_swap_slot(swp_entry_t entry)
	272	{
	273	struct swap_slots_cache *cache;
	274
f07e0f84	275	cache = raw_cpu_ptr(&swp_slots);
a2e16731	276	if (likely(use_swap_slot_cache && cache->slots_ret)) {
67afa38e TC	277	spin_lock_irq(&cache->free_lock);
67afa38e TC	278	/* Swap slots cache may be deactivated before acquiring lock */
f07e0f84	279	if (!use_swap_slot_cache \|\| !cache->slots_ret) {
67afa38e TC	280	spin_unlock_irq(&cache->free_lock);
	281	goto direct_free;
	282	}
	283	if (cache->n_ret >= SWAP_SLOTS_CACHE_SIZE) {
	284	/*
	285	* Return slots to global pool.
	286	* The current swap_map value is SWAP_HAS_CACHE.
	287	* Set it to 0 to indicate it is available for
	288	* allocation in global pool
	289	*/
	290	swapcache_free_entries(cache->slots_ret, cache->n_ret);
	291	cache->n_ret = 0;
	292	}
	293	cache->slots_ret[cache->n_ret++] = entry;
	294	spin_unlock_irq(&cache->free_lock);
	295	} else {
	296	direct_free:
	297	swapcache_free_entries(&entry, 1);
	298	}
67afa38e TC	299
	300	return 0;
	301	}
	302
38d8b4e6	303	swp_entry_t get_swap_page(struct page *page)
67afa38e	304	{
2406b76f	305	swp_entry_t entry;
67afa38e TC	306	struct swap_slots_cache *cache;
67afa38e TC	307
38d8b4e6 HY	308	entry.val = 0;
	309
	310	if (PageTransHuge(page)) {
	311	if (IS_ENABLED(CONFIG_THP_SWAP))
5d5e8f19	312	get_swap_pages(1, &entry, HPAGE_PMD_NR);
bb98f2c5	313	goto out;
38d8b4e6 HY	314	}
38d8b4e6 HY	315
67afa38e TC	316	/*
	317	* Preemption is allowed here, because we may sleep
	318	* in refill_swap_slots_cache(). But it is safe, because
	319	* accesses to the per-CPU data structure are protected by the
	320	* mutex cache->alloc_lock.
	321	*
	322	* The alloc path here does not touch cache->slots_ret
	323	* so cache->free_lock is not taken.
	324	*/
	325	cache = raw_cpu_ptr(&swp_slots);
	326
a2e16731	327	if (likely(check_cache_active() && cache->slots)) {
67afa38e TC	328	mutex_lock(&cache->alloc_lock);
	329	if (cache->slots) {
	330	repeat:
	331	if (cache->nr) {
2406b76f WY	332	entry = cache->slots[cache->cur];
2406b76f WY	333	cache->slots[cache->cur++].val = 0;
67afa38e	334	cache->nr--;
2406b76f WY	335	} else if (refill_swap_slots_cache(cache)) {
2406b76f WY	336	goto repeat;
67afa38e TC	337	}
	338	}
	339	mutex_unlock(&cache->alloc_lock);
	340	if (entry.val)
bb98f2c5	341	goto out;
67afa38e TC	342	}
67afa38e TC	343
5d5e8f19	344	get_swap_pages(1, &entry, 1);
bb98f2c5 TH	345	out:
	346	if (mem_cgroup_try_charge_swap(page, entry)) {
	347	put_swap_page(page, entry);
	348	entry.val = 0;
	349	}
67afa38e TC	350	return entry;
67afa38e TC	351	}