mm/swap_slots.c - linux - Git at Google

 // 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/slab.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 folio_alloc_swap,
 	 * 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 -> folio_alloc_swap
 	 *   -> 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)
 		return 0;

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

 	return cache->nr;
 }

 void 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);
 	}
 }

 swp_entry_t folio_alloc_swap(struct folio *folio)
 {
 	swp_entry_t entry;
 	struct swap_slots_cache *cache;

 	entry.val = 0;

 	if (folio_test_large(folio)) {
 		if (IS_ENABLED(CONFIG_THP_SWAP))
 			get_swap_pages(1, &entry, folio_order(folio));
 		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, 0);
 out:
 	if (mem_cgroup_try_charge_swap(folio, entry)) {
 		put_swap_folio(folio, entry);
 		entry.val = 0;
 	}
 	return entry;
 }
	// 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/slab.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 folio_alloc_swap,
	* 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 -> folio_alloc_swap
	* -> 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)
	return 0;

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

	return cache->nr;
	}

	void 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);
	}
	}

	swp_entry_t folio_alloc_swap(struct folio *folio)
	{
	swp_entry_t entry;
	struct swap_slots_cache *cache;

	entry.val = 0;

	if (folio_test_large(folio)) {
	if (IS_ENABLED(CONFIG_THP_SWAP))
	get_swap_pages(1, &entry, folio_order(folio));
	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, 0);
	out:
	if (mem_cgroup_try_charge_swap(folio, entry)) {
	put_swap_folio(folio, entry);
	entry.val = 0;
	}
	return entry;
	}