[mirror_ubuntu-artful-kernel.git] / mm / swap_slots.c

/*
 * 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>

#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 vzalloc could trigger reclaim and get_swap_page,
	 * which can lock swap_slots_cache_mutex.
	 */
	slots = vzalloc(sizeof(swp_entry_t) * SWAP_SLOTS_CACHE_SIZE);
	if (!slots)
		return -ENOMEM;

	slots_ret = vzalloc(sizeof(swp_entry_t) * SWAP_SLOTS_CACHE_SIZE);
	if (!slots_ret) {
		vfree(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;
	cache->slots = slots;
	slots = NULL;
	cache->slots_ret = slots_ret;
	slots_ret = NULL;
out:
	mutex_unlock(&swap_slots_cache_mutex);
	if (slots)
		vfree(slots);
	if (slots_ret)
		vfree(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) {
			vfree(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)
			vfree(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 (ret < 0)
		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, cache->slots);

	return cache->nr;
}

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

	WARN_ON_ONCE(!swap_slot_cache_initialized);

	cache = &get_cpu_var(swp_slots);
	if (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) {
			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);
	}
	put_cpu_var(swp_slots);

	return 0;
}

swp_entry_t get_swap_page(void)
{
	swp_entry_t entry, *pentry;
	struct swap_slots_cache *cache;

	/*
	 * 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);

	entry.val = 0;
	if (check_cache_active()) {
		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, &entry);

	return entry;
}

#endif /* CONFIG_SWAP */
Commit	Line	Data
67afa38e TC	1	/*
	2	* Manage cache of swap slots to be used for and returned from
	3	* swap.
	4	*
	5	* Copyright(c) 2016 Intel Corporation.
	6	*
	7	* Author: Tim Chen <tim.c.chen@linux.intel.com>
	8	*
	9	* We allocate the swap slots from the global pool and put
	10	* it into local per cpu caches. This has the advantage
	11	* of no needing to acquire the swap_info lock every time
	12	* we need a new slot.
	13	*
	14	* There is also opportunity to simply return the slot
	15	* to local caches without needing to acquire swap_info
	16	* lock. We do not reuse the returned slots directly but
	17	* move them back to the global pool in a batch. This
	18	* allows the slots to coaellesce and reduce fragmentation.
	19	*
	20	* The swap entry allocated is marked with SWAP_HAS_CACHE
	21	* flag in map_count that prevents it from being allocated
	22	* again from the global pool.
	23	*
	24	* The swap slots cache is protected by a mutex instead of
	25	* a spin lock as when we search for slots with scan_swap_map,
	26	* we can possibly sleep.
	27	*/
	28
	29	#include <linux/swap_slots.h>
	30	#include <linux/cpu.h>
	31	#include <linux/cpumask.h>
	32	#include <linux/vmalloc.h>
	33	#include <linux/mutex.h>
	34
	35	#ifdef CONFIG_SWAP
	36
	37	static DEFINE_PER_CPU(struct swap_slots_cache, swp_slots);
	38	static bool swap_slot_cache_active;
ba81f838	39	bool swap_slot_cache_enabled;
67afa38e TC	40	static bool swap_slot_cache_initialized;
	41	DEFINE_MUTEX(swap_slots_cache_mutex);
	42	/* Serialize swap slots cache enable/disable operations */
	43	DEFINE_MUTEX(swap_slots_cache_enable_mutex);
	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
	49	#define use_swap_slot_cache (swap_slot_cache_active && \
	50	swap_slot_cache_enabled && swap_slot_cache_initialized)
	51	#define SLOTS_CACHE 0x1
	52	#define SLOTS_CACHE_RET 0x2
	53
	54	static void deactivate_swap_slots_cache(void)
	55	{
	56	mutex_lock(&swap_slots_cache_mutex);
	57	swap_slot_cache_active = false;
	58	__drain_swap_slots_cache(SLOTS_CACHE\|SLOTS_CACHE_RET);
	59	mutex_unlock(&swap_slots_cache_mutex);
	60	}
	61
	62	static void reactivate_swap_slots_cache(void)
	63	{
	64	mutex_lock(&swap_slots_cache_mutex);
	65	swap_slot_cache_active = true;
	66	mutex_unlock(&swap_slots_cache_mutex);
	67	}
	68
	69	/* Must not be called with cpu hot plug lock */
	70	void disable_swap_slots_cache_lock(void)
	71	{
	72	mutex_lock(&swap_slots_cache_enable_mutex);
	73	swap_slot_cache_enabled = false;
	74	if (swap_slot_cache_initialized) {
	75	/* serialize with cpu hotplug operations */
	76	get_online_cpus();
	77	__drain_swap_slots_cache(SLOTS_CACHE\|SLOTS_CACHE_RET);
	78	put_online_cpus();
	79	}
	80	}
	81
	82	static void __reenable_swap_slots_cache(void)
	83	{
	84	swap_slot_cache_enabled = has_usable_swap();
	85	}
	86
	87	void reenable_swap_slots_cache_unlock(void)
	88	{
	89	__reenable_swap_slots_cache();
	90	mutex_unlock(&swap_slots_cache_enable_mutex);
	91	}
	92
	93	static bool check_cache_active(void)
	94	{
	95	long pages;
	96
	97	if (!swap_slot_cache_enabled \|\| !swap_slot_cache_initialized)
	98	return false;
	99
	100	pages = get_nr_swap_pages();
	101	if (!swap_slot_cache_active) {
	102	if (pages > num_online_cpus() *
	103	THRESHOLD_ACTIVATE_SWAP_SLOTS_CACHE)
104	reactivate_swap_slots_cache();
105	goto out;
106	}
107
108	/* if global pool of slot caches too low, deactivate cache */
109	if (pages < num_online_cpus() * THRESHOLD_DEACTIVATE_SWAP_SLOTS_CACHE)
110	deactivate_swap_slots_cache();
111	out:
112	return swap_slot_cache_active;
113	}
114
115	static int alloc_swap_slot_cache(unsigned int cpu)
116	{
117	struct swap_slots_cache *cache;
118	swp_entry_t slots, slots_ret;
119
120	/*
121	* Do allocation outside swap_slots_cache_mutex
122	* as vzalloc could trigger reclaim and get_swap_page,
123	* which can lock swap_slots_cache_mutex.
124	*/
125	slots = vzalloc(sizeof(swp_entry_t) * SWAP_SLOTS_CACHE_SIZE);
126	if (!slots)
127	return -ENOMEM;
128
129	slots_ret = vzalloc(sizeof(swp_entry_t) * SWAP_SLOTS_CACHE_SIZE);
130	if (!slots_ret) {
131	vfree(slots);
132	return -ENOMEM;
133	}
134
135	mutex_lock(&swap_slots_cache_mutex);
136	cache = &per_cpu(swp_slots, cpu);
137	if (cache->slots \|\| cache->slots_ret)
138	/* cache already allocated */
139	goto out;
140	if (!cache->lock_initialized) {
141	mutex_init(&cache->alloc_lock);
142	spin_lock_init(&cache->free_lock);
143	cache->lock_initialized = true;
144	}
145	cache->nr = 0;
146	cache->cur = 0;
147	cache->n_ret = 0;
148	cache->slots = slots;
149	slots = NULL;
150	cache->slots_ret = slots_ret;
151	slots_ret = NULL;
152	out:
153	mutex_unlock(&swap_slots_cache_mutex);
154	if (slots)
155	vfree(slots);
156	if (slots_ret)
157	vfree(slots_ret);
158	return 0;
159	}
160
161	static void drain_slots_cache_cpu(unsigned int cpu, unsigned int type,
162	bool free_slots)
163	{
164	struct swap_slots_cache *cache;
165	swp_entry_t *slots = NULL;
166
167	cache = &per_cpu(swp_slots, cpu);
168	if ((type & SLOTS_CACHE) && cache->slots) {
169	mutex_lock(&cache->alloc_lock);
170	swapcache_free_entries(cache->slots + cache->cur, cache->nr);
171	cache->cur = 0;
172	cache->nr = 0;
173	if (free_slots && cache->slots) {
174	vfree(cache->slots);
175	cache->slots = NULL;
176	}
177	mutex_unlock(&cache->alloc_lock);
178	}
179	if ((type & SLOTS_CACHE_RET) && cache->slots_ret) {
180	spin_lock_irq(&cache->free_lock);
181	swapcache_free_entries(cache->slots_ret, cache->n_ret);
182	cache->n_ret = 0;
183	if (free_slots && cache->slots_ret) {
184	slots = cache->slots_ret;
185	cache->slots_ret = NULL;
186	}
187	spin_unlock_irq(&cache->free_lock);
188	if (slots)
189	vfree(slots);
190	}
191	}
192
193	static void __drain_swap_slots_cache(unsigned int type)
194	{
195	unsigned int cpu;
196
197	/*
198	* This function is called during
199	* 1) swapoff, when we have to make sure no
200	* left over slots are in cache when we remove
201	* a swap device;
202	* 2) disabling of swap slot cache, when we run low
203	* on swap slots when allocating memory and need
204	* to return swap slots to global pool.
205	*
206	* We cannot acquire cpu hot plug lock here as
207	* this function can be invoked in the cpu
208	* hot plug path:
209	* cpu_up -> lock cpu_hotplug -> cpu hotplug state callback
210	* -> memory allocation -> direct reclaim -> get_swap_page
211	* -> drain_swap_slots_cache
212	*
213	* Hence the loop over current online cpu below could miss cpu that
214	* is being brought online but not yet marked as online.
215	* That is okay as we do not schedule and run anything on a
216	* cpu before it has been marked online. Hence, we will not
217	* fill any swap slots in slots cache of such cpu.
218	* There are no slots on such cpu that need to be drained.
219	*/
220	for_each_online_cpu(cpu)
221	drain_slots_cache_cpu(cpu, type, false);
222	}
223
224	static int free_slot_cache(unsigned int cpu)
225	{
226	mutex_lock(&swap_slots_cache_mutex);
227	drain_slots_cache_cpu(cpu, SLOTS_CACHE \| SLOTS_CACHE_RET, true);
228	mutex_unlock(&swap_slots_cache_mutex);
229	return 0;
230	}
231
232	int enable_swap_slots_cache(void)
233	{
234	int ret = 0;
235
236	mutex_lock(&swap_slots_cache_enable_mutex);
237	if (swap_slot_cache_initialized) {
238	__reenable_swap_slots_cache();
239	goto out_unlock;
240	}
241
242	ret = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "swap_slots_cache",
243	alloc_swap_slot_cache, free_slot_cache);
244	if (ret < 0)
245	goto out_unlock;
246	swap_slot_cache_initialized = true;
247	__reenable_swap_slots_cache();
248	out_unlock:
249	mutex_unlock(&swap_slots_cache_enable_mutex);
250	return 0;
251	}
252
253	/* called with swap slot cache's alloc lock held */
254	static int refill_swap_slots_cache(struct swap_slots_cache *cache)
255	{
256	if (!use_swap_slot_cache \|\| cache->nr)
257	return 0;
258
259	cache->cur = 0;
260	if (swap_slot_cache_active)
261	cache->nr = get_swap_pages(SWAP_SLOTS_CACHE_SIZE, cache->slots);
262
263	return cache->nr;
264	}
265
266	int free_swap_slot(swp_entry_t entry)
267	{
268	struct swap_slots_cache *cache;
269
452b94b8	270	WARN_ON_ONCE(!swap_slot_cache_initialized);
67afa38e TC	271
	272	cache = &get_cpu_var(swp_slots);
	273	if (use_swap_slot_cache && cache->slots_ret) {
	274	spin_lock_irq(&cache->free_lock);
	275	/* Swap slots cache may be deactivated before acquiring lock */
	276	if (!use_swap_slot_cache) {
	277	spin_unlock_irq(&cache->free_lock);
	278	goto direct_free;
	279	}
	280	if (cache->n_ret >= SWAP_SLOTS_CACHE_SIZE) {
	281	/*
	282	* Return slots to global pool.
	283	* The current swap_map value is SWAP_HAS_CACHE.
	284	* Set it to 0 to indicate it is available for
	285	* allocation in global pool
	286	*/
	287	swapcache_free_entries(cache->slots_ret, cache->n_ret);
	288	cache->n_ret = 0;
	289	}
	290	cache->slots_ret[cache->n_ret++] = entry;
	291	spin_unlock_irq(&cache->free_lock);
	292	} else {
	293	direct_free:
	294	swapcache_free_entries(&entry, 1);
	295	}
	296	put_cpu_var(swp_slots);
	297
	298	return 0;
	299	}
	300
	301	swp_entry_t get_swap_page(void)
	302	{
	303	swp_entry_t entry, *pentry;
	304	struct swap_slots_cache *cache;
	305
	306	/*
	307	* Preemption is allowed here, because we may sleep
	308	* in refill_swap_slots_cache(). But it is safe, because
	309	* accesses to the per-CPU data structure are protected by the
	310	* mutex cache->alloc_lock.
	311	*
	312	* The alloc path here does not touch cache->slots_ret
	313	* so cache->free_lock is not taken.
	314	*/
	315	cache = raw_cpu_ptr(&swp_slots);
	316
	317	entry.val = 0;
	318	if (check_cache_active()) {
	319	mutex_lock(&cache->alloc_lock);
	320	if (cache->slots) {
	321	repeat:
	322	if (cache->nr) {
	323	pentry = &cache->slots[cache->cur++];
	324	entry = *pentry;
	325	pentry->val = 0;
	326	cache->nr--;
	327	} else {
	328	if (refill_swap_slots_cache(cache))
	329	goto repeat;
	330	}
	331	}
	332	mutex_unlock(&cache->alloc_lock);
	333	if (entry.val)
	334	return entry;
335	}
336
337	get_swap_pages(1, &entry);
338
339	return entry;
340	}
341
342	#endif /* CONFIG_SWAP */