mm/vmpressure.c - kernel/msm-4.9 - Gitiles

 /*
  * Linux VM pressure
  *
  * Copyright 2012 Linaro Ltd.
  *		  Anton Vorontsov <anton.vorontsov@linaro.org>
  *
  * Based on ideas from Andrew Morton, David Rientjes, KOSAKI Motohiro,
  * Leonid Moiseichuk, Mel Gorman, Minchan Kim and Pekka Enberg.
  *
  * This program is free software; you can redistribute it and/or modify it
  * under the terms of the GNU General Public License version 2 as published
  * by the Free Software Foundation.
  */

 #include <linux/cgroup.h>
 #include <linux/fs.h>
 #include <linux/log2.h>
 #include <linux/sched.h>
 #include <linux/mm.h>
 #include <linux/vmstat.h>
 #include <linux/eventfd.h>
 #include <linux/slab.h>
 #include <linux/swap.h>
 #include <linux/printk.h>
 #include <linux/notifier.h>
 #include <linux/init.h>
 #include <linux/vmpressure.h>

 /*
  * The window size (vmpressure_win) is the number of scanned pages before
  * we try to analyze scanned/reclaimed ratio. So the window is used as a
  * rate-limit tunable for the "low" level notification, and also for
  * averaging the ratio for medium/critical levels. Using small window
  * sizes can cause lot of false positives, but too big window size will
  * delay the notifications.
  *
  * As the vmscan reclaimer logic works with chunks which are multiple of
  * SWAP_CLUSTER_MAX, it makes sense to use it for the window size as well.
  *
  * TODO: Make the window size depend on machine size, as we do for vmstat
  * thresholds. Currently we set it to 512 pages (2MB for 4KB pages).
  */
 static const unsigned long vmpressure_win = SWAP_CLUSTER_MAX * 16;

 /*
  * These thresholds are used when we account memory pressure through
  * scanned/reclaimed ratio. The current values were chosen empirically. In
  * essence, they are percents: the higher the value, the more number
  * unsuccessful reclaims there were.
  */
 static const unsigned int vmpressure_level_med = 60;
 static const unsigned int vmpressure_level_critical = 95;

 static struct vmpressure global_vmpressure;
 static BLOCKING_NOTIFIER_HEAD(vmpressure_notifier);

 int vmpressure_notifier_register(struct notifier_block *nb)
 {
 	return blocking_notifier_chain_register(&vmpressure_notifier, nb);
 }

 int vmpressure_notifier_unregister(struct notifier_block *nb)
 {
 	return blocking_notifier_chain_unregister(&vmpressure_notifier, nb);
 }

 static void vmpressure_notify(unsigned long pressure)
 {
 	blocking_notifier_call_chain(&vmpressure_notifier, pressure, NULL);
 }

 /*
  * When there are too little pages left to scan, vmpressure() may miss the
  * critical pressure as number of pages will be less than "window size".
  * However, in that case the vmscan priority will raise fast as the
  * reclaimer will try to scan LRUs more deeply.
  *
  * The vmscan logic considers these special priorities:
  *
  * prio == DEF_PRIORITY (12): reclaimer starts with that value
  * prio <= DEF_PRIORITY - 2 : kswapd becomes somewhat overwhelmed
  * prio == 0                : close to OOM, kernel scans every page in an lru
  *
  * Any value in this range is acceptable for this tunable (i.e. from 12 to
  * 0). Current value for the vmpressure_level_critical_prio is chosen
  * empirically, but the number, in essence, means that we consider
  * critical level when scanning depth is ~10% of the lru size (vmscan
  * scans 'lru_size >> prio' pages, so it is actually 12.5%, or one
  * eights).
  */
 static const unsigned int vmpressure_level_critical_prio = ilog2(100 / 10);

 static struct vmpressure *work_to_vmpressure(struct work_struct *work)
 {
 	return container_of(work, struct vmpressure, work);
 }

 #ifdef CONFIG_MEMCG
 static struct vmpressure *vmpressure_parent(struct vmpressure *vmpr)
 {
 	struct cgroup_subsys_state *css = vmpressure_to_css(vmpr);
 	struct mem_cgroup *memcg = mem_cgroup_from_css(css);

 	memcg = parent_mem_cgroup(memcg);
 	if (!memcg)
 		return NULL;
 	return memcg_to_vmpressure(memcg);
 }
 #else
 static struct vmpressure *vmpressure_parent(struct vmpressure *vmpr)
 {
 	return NULL;
 }
 #endif

 enum vmpressure_levels {
 	VMPRESSURE_LOW = 0,
 	VMPRESSURE_MEDIUM,
 	VMPRESSURE_CRITICAL,
 	VMPRESSURE_NUM_LEVELS,
 };

 static const char * const vmpressure_str_levels[] = {
 	[VMPRESSURE_LOW] = "low",
 	[VMPRESSURE_MEDIUM] = "medium",
 	[VMPRESSURE_CRITICAL] = "critical",
 };

 static enum vmpressure_levels vmpressure_level(unsigned long pressure)
 {
 	if (pressure >= vmpressure_level_critical)
 		return VMPRESSURE_CRITICAL;
 	else if (pressure >= vmpressure_level_med)
 		return VMPRESSURE_MEDIUM;
 	return VMPRESSURE_LOW;
 }

 static unsigned long vmpressure_calc_pressure(unsigned long scanned,
 						    unsigned long reclaimed)
 {
 	unsigned long scale = scanned + reclaimed;
 	unsigned long pressure = 0;

 	/*
 	 * reclaimed can be greater than scanned in cases
 	 * like THP, where the scanned is 1 and reclaimed
 	 * could be 512
 	 */
 	if (reclaimed >= scanned)
 		goto out;
 	/*
 	 * We calculate the ratio (in percents) of how many pages were
 	 * scanned vs. reclaimed in a given time frame (window). Note that
 	 * time is in VM reclaimer's "ticks", i.e. number of pages
 	 * scanned. This makes it possible to set desired reaction time
 	 * and serves as a ratelimit.
 	 */
 	pressure = scale - (reclaimed * scale / scanned);
 	pressure = pressure * 100 / scale;

 out:
 	pr_debug("%s: %3lu  (s: %lu  r: %lu)\n", __func__, pressure,
 		 scanned, reclaimed);

 	return pressure;
 }

 struct vmpressure_event {
 	struct eventfd_ctx *efd;
 	enum vmpressure_levels level;
 	struct list_head node;
 };

 static bool vmpressure_event(struct vmpressure *vmpr,
 			     enum vmpressure_levels level)
 {
 	struct vmpressure_event *ev;
 	bool signalled = false;

 	mutex_lock(&vmpr->events_lock);

 	list_for_each_entry(ev, &vmpr->events, node) {
 		if (level >= ev->level) {
 			eventfd_signal(ev->efd, 1);
 			signalled = true;
 		}
 	}

 	mutex_unlock(&vmpr->events_lock);

 	return signalled;
 }

 static void vmpressure_work_fn(struct work_struct *work)
 {
 	struct vmpressure *vmpr = work_to_vmpressure(work);
 	unsigned long scanned;
 	unsigned long reclaimed;
 	unsigned long pressure;
 	enum vmpressure_levels level;

 	spin_lock(&vmpr->sr_lock);
 	/*
 	 * Several contexts might be calling vmpressure(), so it is
 	 * possible that the work was rescheduled again before the old
 	 * work context cleared the counters. In that case we will run
 	 * just after the old work returns, but then scanned might be zero
 	 * here. No need for any locks here since we don't care if
 	 * vmpr->reclaimed is in sync.
 	 */
 	scanned = vmpr->tree_scanned;
 	if (!scanned) {
 		spin_unlock(&vmpr->sr_lock);
 		return;
 	}

 	reclaimed = vmpr->tree_reclaimed;
 	vmpr->tree_scanned = 0;
 	vmpr->tree_reclaimed = 0;
 	spin_unlock(&vmpr->sr_lock);

 	pressure = vmpressure_calc_pressure(scanned, reclaimed);
 	level = vmpressure_level(pressure);

 	do {
 		if (vmpressure_event(vmpr, level))
 			break;
 		/*
 		 * If not handled, propagate the event upward into the
 		 * hierarchy.
 		 */
 	} while ((vmpr = vmpressure_parent(vmpr)));
 }

 #ifdef CONFIG_MEMCG
 static void vmpressure_memcg(gfp_t gfp, struct mem_cgroup *memcg, bool tree,
 		unsigned long scanned, unsigned long reclaimed)
 {
 	struct vmpressure *vmpr = memcg_to_vmpressure(memcg);

 	/*
 	 * Here we only want to account pressure that userland is able to
 	 * help us with. For example, suppose that DMA zone is under
 	 * pressure; if we notify userland about that kind of pressure,
 	 * then it will be mostly a waste as it will trigger unnecessary
 	 * freeing of memory by userland (since userland is more likely to
 	 * have HIGHMEM/MOVABLE pages instead of the DMA fallback). That
 	 * is why we include only movable, highmem and FS/IO pages.
 	 * Indirect reclaim (kswapd) sets sc->gfp_mask to GFP_KERNEL, so
 	 * we account it too.
 	 */
 	if (!(gfp & (__GFP_HIGHMEM | __GFP_MOVABLE | __GFP_IO | __GFP_FS)))
 		return;

 	/*
 	 * If we got here with no pages scanned, then that is an indicator
 	 * that reclaimer was unable to find any shrinkable LRUs at the
 	 * current scanning depth. But it does not mean that we should
 	 * report the critical pressure, yet. If the scanning priority
 	 * (scanning depth) goes too high (deep), we will be notified
 	 * through vmpressure_prio(). But so far, keep calm.
 	 */
 	if (!scanned)
 		return;

 	if (tree) {
 		spin_lock(&vmpr->sr_lock);
 		scanned = vmpr->tree_scanned += scanned;
 		vmpr->tree_reclaimed += reclaimed;
 		spin_unlock(&vmpr->sr_lock);

 		if (scanned < vmpressure_win)
 			return;
 		schedule_work(&vmpr->work);
 	} else {
 		enum vmpressure_levels level;
 		unsigned long pressure;

 		/* For now, no users for root-level efficiency */
 		if (!memcg || memcg == root_mem_cgroup)
 			return;

 		spin_lock(&vmpr->sr_lock);
 		scanned = vmpr->scanned += scanned;
 		reclaimed = vmpr->reclaimed += reclaimed;
 		if (scanned < vmpressure_win) {
 			spin_unlock(&vmpr->sr_lock);
 			return;
 		}
 		vmpr->scanned = vmpr->reclaimed = 0;
 		spin_unlock(&vmpr->sr_lock);

 		pressure = vmpressure_calc_pressure(scanned, reclaimed);
 		level = vmpressure_level(pressure);

 		if (level > VMPRESSURE_LOW) {
 			/*
 			 * Let the socket buffer allocator know that
 			 * we are having trouble reclaiming LRU pages.
 			 *
 			 * For hysteresis keep the pressure state
 			 * asserted for a second in which subsequent
 			 * pressure events can occur.
 			 */
 			memcg->socket_pressure = jiffies + HZ;
 		}
 	}
 }
 #else
 static void vmpressure_memcg(gfp_t gfp, struct mem_cgroup *memcg, bool tree,
 		unsigned long scanned, unsigned long reclaimed) { }
 #endif

 static void vmpressure_global(gfp_t gfp, unsigned long scanned,
 		unsigned long reclaimed)
 {
 	struct vmpressure *vmpr = &global_vmpressure;
 	unsigned long pressure;

 	if (!(gfp & (__GFP_HIGHMEM | __GFP_MOVABLE | __GFP_IO | __GFP_FS)))
 		return;

 	if (!scanned)
 		return;

 	spin_lock(&vmpr->sr_lock);
 	vmpr->scanned += scanned;
 	vmpr->reclaimed += reclaimed;
 	scanned = vmpr->scanned;
 	reclaimed = vmpr->reclaimed;
 	spin_unlock(&vmpr->sr_lock);

 	if (scanned < vmpressure_win)
 		return;

 	spin_lock(&vmpr->sr_lock);
 	vmpr->scanned = 0;
 	vmpr->reclaimed = 0;
 	spin_unlock(&vmpr->sr_lock);

 	pressure = vmpressure_calc_pressure(scanned, reclaimed);
 	vmpressure_notify(pressure);
 }

 /**
  * vmpressure() - Account memory pressure through scanned/reclaimed ratio
  * @gfp:	reclaimer's gfp mask
  * @memcg:	cgroup memory controller handle
  * @tree:	legacy subtree mode
  * @scanned:	number of pages scanned
  * @reclaimed:	number of pages reclaimed
  *
  * This function should be called from the vmscan reclaim path to account
  * "instantaneous" memory pressure (scanned/reclaimed ratio). The raw
  * pressure index is then further refined and averaged over time.
  *
  * If @tree is set, vmpressure is in traditional userspace reporting
  * mode: @memcg is considered the pressure root and userspace is
  * notified of the entire subtree's reclaim efficiency.
  *
  * If @tree is not set, reclaim efficiency is recorded for @memcg, and
  * only in-kernel users are notified.
  *
  * This function does not return any value.
  */
 void vmpressure(gfp_t gfp, struct mem_cgroup *memcg, bool tree,
 		unsigned long scanned, unsigned long reclaimed)
 {
 	if (!memcg)
 		vmpressure_global(gfp, scanned, reclaimed);

 	if (IS_ENABLED(CONFIG_MEMCG))
 		vmpressure_memcg(gfp, memcg, tree, scanned, reclaimed);
 }

 /**
  * vmpressure_prio() - Account memory pressure through reclaimer priority level
  * @gfp:	reclaimer's gfp mask
  * @memcg:	cgroup memory controller handle
  * @prio:	reclaimer's priority
  *
  * This function should be called from the reclaim path every time when
  * the vmscan's reclaiming priority (scanning depth) changes.
  *
  * This function does not return any value.
  */
 void vmpressure_prio(gfp_t gfp, struct mem_cgroup *memcg, int prio)
 {
 	/*
 	 * We only use prio for accounting critical level. For more info
 	 * see comment for vmpressure_level_critical_prio variable above.
 	 */
 	if (prio > vmpressure_level_critical_prio)
 		return;

 	/*
 	 * OK, the prio is below the threshold, updating vmpressure
 	 * information before shrinker dives into long shrinking of long
 	 * range vmscan. Passing scanned = vmpressure_win, reclaimed = 0
 	 * to the vmpressure() basically means that we signal 'critical'
 	 * level.
 	 */
 	vmpressure(gfp, memcg, true, vmpressure_win, 0);
 }

 /**
  * vmpressure_register_event() - Bind vmpressure notifications to an eventfd
  * @memcg:	memcg that is interested in vmpressure notifications
  * @eventfd:	eventfd context to link notifications with
  * @args:	event arguments (used to set up a pressure level threshold)
  *
  * This function associates eventfd context with the vmpressure
  * infrastructure, so that the notifications will be delivered to the
  * @eventfd. The @args parameter is a string that denotes pressure level
  * threshold (one of vmpressure_str_levels, i.e. "low", "medium", or
  * "critical").
  *
  * To be used as memcg event method.
  */
 int vmpressure_register_event(struct mem_cgroup *memcg,
 			      struct eventfd_ctx *eventfd, const char *args)
 {
 	struct vmpressure *vmpr = memcg_to_vmpressure(memcg);
 	struct vmpressure_event *ev;
 	int level;

 	for (level = 0; level < VMPRESSURE_NUM_LEVELS; level++) {
 		if (!strcmp(vmpressure_str_levels[level], args))
 			break;
 	}

 	if (level >= VMPRESSURE_NUM_LEVELS)
 		return -EINVAL;

 	ev = kzalloc(sizeof(*ev), GFP_KERNEL);
 	if (!ev)
 		return -ENOMEM;

 	ev->efd = eventfd;
 	ev->level = level;

 	mutex_lock(&vmpr->events_lock);
 	list_add(&ev->node, &vmpr->events);
 	mutex_unlock(&vmpr->events_lock);

 	return 0;
 }

 /**
  * vmpressure_unregister_event() - Unbind eventfd from vmpressure
  * @memcg:	memcg handle
  * @eventfd:	eventfd context that was used to link vmpressure with the @cg
  *
  * This function does internal manipulations to detach the @eventfd from
  * the vmpressure notifications, and then frees internal resources
  * associated with the @eventfd (but the @eventfd itself is not freed).
  *
  * To be used as memcg event method.
  */
 void vmpressure_unregister_event(struct mem_cgroup *memcg,
 				 struct eventfd_ctx *eventfd)
 {
 	struct vmpressure *vmpr = memcg_to_vmpressure(memcg);
 	struct vmpressure_event *ev;

 	mutex_lock(&vmpr->events_lock);
 	list_for_each_entry(ev, &vmpr->events, node) {
 		if (ev->efd != eventfd)
 			continue;
 		list_del(&ev->node);
 		kfree(ev);
 		break;
 	}
 	mutex_unlock(&vmpr->events_lock);
 }

 /**
  * vmpressure_init() - Initialize vmpressure control structure
  * @vmpr:	Structure to be initialized
  *
  * This function should be called on every allocated vmpressure structure
  * before any usage.
  */
 void vmpressure_init(struct vmpressure *vmpr)
 {
 	spin_lock_init(&vmpr->sr_lock);
 	mutex_init(&vmpr->events_lock);
 	INIT_LIST_HEAD(&vmpr->events);
 	INIT_WORK(&vmpr->work, vmpressure_work_fn);
 }

 /**
  * vmpressure_cleanup() - shuts down vmpressure control structure
  * @vmpr:	Structure to be cleaned up
  *
  * This function should be called before the structure in which it is
  * embedded is cleaned up.
  */
 void vmpressure_cleanup(struct vmpressure *vmpr)
 {
 	/*
 	 * Make sure there is no pending work before eventfd infrastructure
 	 * goes away.
 	 */
 	flush_work(&vmpr->work);
 }

 static int vmpressure_global_init(void)
 {
 	vmpressure_init(&global_vmpressure);
 	return 0;
 }
 late_initcall(vmpressure_global_init);
	/*
	* Linux VM pressure
	*
	* Copyright 2012 Linaro Ltd.
	* Anton Vorontsov <anton.vorontsov@linaro.org>
	*
	* Based on ideas from Andrew Morton, David Rientjes, KOSAKI Motohiro,
	* Leonid Moiseichuk, Mel Gorman, Minchan Kim and Pekka Enberg.
	*
	* This program is free software; you can redistribute it and/or modify it
	* under the terms of the GNU General Public License version 2 as published
	* by the Free Software Foundation.
	*/

	#include <linux/cgroup.h>
	#include <linux/fs.h>
	#include <linux/log2.h>
	#include <linux/sched.h>
	#include <linux/mm.h>
	#include <linux/vmstat.h>
	#include <linux/eventfd.h>
	#include <linux/slab.h>
	#include <linux/swap.h>
	#include <linux/printk.h>
	#include <linux/notifier.h>
	#include <linux/init.h>
	#include <linux/vmpressure.h>

	/*
	* The window size (vmpressure_win) is the number of scanned pages before
	* we try to analyze scanned/reclaimed ratio. So the window is used as a
	* rate-limit tunable for the "low" level notification, and also for
	* averaging the ratio for medium/critical levels. Using small window
	* sizes can cause lot of false positives, but too big window size will
	* delay the notifications.
	*
	* As the vmscan reclaimer logic works with chunks which are multiple of
	* SWAP_CLUSTER_MAX, it makes sense to use it for the window size as well.
	*
	* TODO: Make the window size depend on machine size, as we do for vmstat
	* thresholds. Currently we set it to 512 pages (2MB for 4KB pages).
	*/
	static const unsigned long vmpressure_win = SWAP_CLUSTER_MAX * 16;

	/*
	* These thresholds are used when we account memory pressure through
	* scanned/reclaimed ratio. The current values were chosen empirically. In
	* essence, they are percents: the higher the value, the more number
	* unsuccessful reclaims there were.
	*/
	static const unsigned int vmpressure_level_med = 60;
	static const unsigned int vmpressure_level_critical = 95;

	static struct vmpressure global_vmpressure;
	static BLOCKING_NOTIFIER_HEAD(vmpressure_notifier);

	int vmpressure_notifier_register(struct notifier_block *nb)
	{
	return blocking_notifier_chain_register(&vmpressure_notifier, nb);
	}

	int vmpressure_notifier_unregister(struct notifier_block *nb)
	{
	return blocking_notifier_chain_unregister(&vmpressure_notifier, nb);
	}

	static void vmpressure_notify(unsigned long pressure)
	{
	blocking_notifier_call_chain(&vmpressure_notifier, pressure, NULL);
	}

	/*
	* When there are too little pages left to scan, vmpressure() may miss the
	* critical pressure as number of pages will be less than "window size".
	* However, in that case the vmscan priority will raise fast as the
	* reclaimer will try to scan LRUs more deeply.
	*
	* The vmscan logic considers these special priorities:
	*
	* prio == DEF_PRIORITY (12): reclaimer starts with that value
	* prio <= DEF_PRIORITY - 2 : kswapd becomes somewhat overwhelmed
	* prio == 0 : close to OOM, kernel scans every page in an lru
	*
	* Any value in this range is acceptable for this tunable (i.e. from 12 to
	* 0). Current value for the vmpressure_level_critical_prio is chosen
	* empirically, but the number, in essence, means that we consider
	* critical level when scanning depth is ~10% of the lru size (vmscan
	* scans 'lru_size >> prio' pages, so it is actually 12.5%, or one
	* eights).
	*/
	static const unsigned int vmpressure_level_critical_prio = ilog2(100 / 10);

	static struct vmpressure work_to_vmpressure(struct work_struct work)
	{
	return container_of(work, struct vmpressure, work);
	}

	#ifdef CONFIG_MEMCG
	static struct vmpressure vmpressure_parent(struct vmpressure vmpr)
	{
	struct cgroup_subsys_state *css = vmpressure_to_css(vmpr);
	struct mem_cgroup *memcg = mem_cgroup_from_css(css);

	memcg = parent_mem_cgroup(memcg);
	if (!memcg)
	return NULL;
	return memcg_to_vmpressure(memcg);
	}
	#else
	static struct vmpressure vmpressure_parent(struct vmpressure vmpr)
	{
	return NULL;
	}
	#endif

	enum vmpressure_levels {
	VMPRESSURE_LOW = 0,
	VMPRESSURE_MEDIUM,
	VMPRESSURE_CRITICAL,
	VMPRESSURE_NUM_LEVELS,
	};

	static const char * const vmpressure_str_levels[] = {
	[VMPRESSURE_LOW] = "low",
	[VMPRESSURE_MEDIUM] = "medium",
	[VMPRESSURE_CRITICAL] = "critical",
	};

	static enum vmpressure_levels vmpressure_level(unsigned long pressure)
	{
	if (pressure >= vmpressure_level_critical)
	return VMPRESSURE_CRITICAL;
	else if (pressure >= vmpressure_level_med)
	return VMPRESSURE_MEDIUM;
	return VMPRESSURE_LOW;
	}

	static unsigned long vmpressure_calc_pressure(unsigned long scanned,
	unsigned long reclaimed)
	{
	unsigned long scale = scanned + reclaimed;
	unsigned long pressure = 0;

	/*
	* reclaimed can be greater than scanned in cases
	* like THP, where the scanned is 1 and reclaimed
	* could be 512
	*/
	if (reclaimed >= scanned)
	goto out;
	/*
	* We calculate the ratio (in percents) of how many pages were
	* scanned vs. reclaimed in a given time frame (window). Note that
	* time is in VM reclaimer's "ticks", i.e. number of pages
	* scanned. This makes it possible to set desired reaction time
	* and serves as a ratelimit.
	*/
	pressure = scale - (reclaimed * scale / scanned);
	pressure = pressure * 100 / scale;

	out:
	pr_debug("%s: %3lu (s: %lu r: %lu)\n", __func__, pressure,
	scanned, reclaimed);

	return pressure;
	}

	struct vmpressure_event {
	struct eventfd_ctx *efd;
	enum vmpressure_levels level;
	struct list_head node;
	};

	static bool vmpressure_event(struct vmpressure *vmpr,
	enum vmpressure_levels level)
	{
	struct vmpressure_event *ev;
	bool signalled = false;

	mutex_lock(&vmpr->events_lock);

	list_for_each_entry(ev, &vmpr->events, node) {
	if (level >= ev->level) {
	eventfd_signal(ev->efd, 1);
	signalled = true;
	}
	}

	mutex_unlock(&vmpr->events_lock);

	return signalled;
	}

	static void vmpressure_work_fn(struct work_struct *work)
	{
	struct vmpressure *vmpr = work_to_vmpressure(work);
	unsigned long scanned;
	unsigned long reclaimed;
	unsigned long pressure;
	enum vmpressure_levels level;

	spin_lock(&vmpr->sr_lock);
	/*
	* Several contexts might be calling vmpressure(), so it is
	* possible that the work was rescheduled again before the old
	* work context cleared the counters. In that case we will run
	* just after the old work returns, but then scanned might be zero
	* here. No need for any locks here since we don't care if
	* vmpr->reclaimed is in sync.
	*/
	scanned = vmpr->tree_scanned;
	if (!scanned) {
	spin_unlock(&vmpr->sr_lock);
	return;
	}

	reclaimed = vmpr->tree_reclaimed;
	vmpr->tree_scanned = 0;
	vmpr->tree_reclaimed = 0;
	spin_unlock(&vmpr->sr_lock);

	pressure = vmpressure_calc_pressure(scanned, reclaimed);
	level = vmpressure_level(pressure);

	do {
	if (vmpressure_event(vmpr, level))
	break;
	/*
	* If not handled, propagate the event upward into the
	* hierarchy.
	*/
	} while ((vmpr = vmpressure_parent(vmpr)));
	}

	#ifdef CONFIG_MEMCG
	static void vmpressure_memcg(gfp_t gfp, struct mem_cgroup *memcg, bool tree,
	unsigned long scanned, unsigned long reclaimed)
	{
	struct vmpressure *vmpr = memcg_to_vmpressure(memcg);

	/*
	* Here we only want to account pressure that userland is able to
	* help us with. For example, suppose that DMA zone is under
	* pressure; if we notify userland about that kind of pressure,
	* then it will be mostly a waste as it will trigger unnecessary
	* freeing of memory by userland (since userland is more likely to
	* have HIGHMEM/MOVABLE pages instead of the DMA fallback). That
	* is why we include only movable, highmem and FS/IO pages.
	* Indirect reclaim (kswapd) sets sc->gfp_mask to GFP_KERNEL, so
	* we account it too.
	*/
	if (!(gfp & (__GFP_HIGHMEM \| __GFP_MOVABLE \| __GFP_IO \| __GFP_FS)))
	return;

	/*
	* If we got here with no pages scanned, then that is an indicator
	* that reclaimer was unable to find any shrinkable LRUs at the
	* current scanning depth. But it does not mean that we should
	* report the critical pressure, yet. If the scanning priority
	* (scanning depth) goes too high (deep), we will be notified
	* through vmpressure_prio(). But so far, keep calm.
	*/
	if (!scanned)
	return;

	if (tree) {
	spin_lock(&vmpr->sr_lock);
	scanned = vmpr->tree_scanned += scanned;
	vmpr->tree_reclaimed += reclaimed;
	spin_unlock(&vmpr->sr_lock);

	if (scanned < vmpressure_win)
	return;
	schedule_work(&vmpr->work);
	} else {
	enum vmpressure_levels level;
	unsigned long pressure;

	/* For now, no users for root-level efficiency */
	if (!memcg \|\| memcg == root_mem_cgroup)
	return;

	spin_lock(&vmpr->sr_lock);
	scanned = vmpr->scanned += scanned;
	reclaimed = vmpr->reclaimed += reclaimed;
	if (scanned < vmpressure_win) {
	spin_unlock(&vmpr->sr_lock);
	return;
	}
	vmpr->scanned = vmpr->reclaimed = 0;
	spin_unlock(&vmpr->sr_lock);

	pressure = vmpressure_calc_pressure(scanned, reclaimed);
	level = vmpressure_level(pressure);

	if (level > VMPRESSURE_LOW) {
	/*
	* Let the socket buffer allocator know that
	* we are having trouble reclaiming LRU pages.
	*
	* For hysteresis keep the pressure state
	* asserted for a second in which subsequent
	* pressure events can occur.
	*/
	memcg->socket_pressure = jiffies + HZ;
	}
	}
	}
	#else
	static void vmpressure_memcg(gfp_t gfp, struct mem_cgroup *memcg, bool tree,
	unsigned long scanned, unsigned long reclaimed) { }
	#endif

	static void vmpressure_global(gfp_t gfp, unsigned long scanned,
	unsigned long reclaimed)
	{
	struct vmpressure *vmpr = &global_vmpressure;
	unsigned long pressure;

	if (!(gfp & (__GFP_HIGHMEM \| __GFP_MOVABLE \| __GFP_IO \| __GFP_FS)))
	return;

	if (!scanned)
	return;

	spin_lock(&vmpr->sr_lock);
	vmpr->scanned += scanned;
	vmpr->reclaimed += reclaimed;
	scanned = vmpr->scanned;
	reclaimed = vmpr->reclaimed;
	spin_unlock(&vmpr->sr_lock);

	if (scanned < vmpressure_win)
	return;

	spin_lock(&vmpr->sr_lock);
	vmpr->scanned = 0;
	vmpr->reclaimed = 0;
	spin_unlock(&vmpr->sr_lock);

	pressure = vmpressure_calc_pressure(scanned, reclaimed);
	vmpressure_notify(pressure);
	}

	/**
	* vmpressure() - Account memory pressure through scanned/reclaimed ratio
	* @gfp: reclaimer's gfp mask
	* @memcg: cgroup memory controller handle
	* @tree: legacy subtree mode
	* @scanned: number of pages scanned
	* @reclaimed: number of pages reclaimed
	*
	* This function should be called from the vmscan reclaim path to account
	* "instantaneous" memory pressure (scanned/reclaimed ratio). The raw
	* pressure index is then further refined and averaged over time.
	*
	* If @tree is set, vmpressure is in traditional userspace reporting
	* mode: @memcg is considered the pressure root and userspace is
	* notified of the entire subtree's reclaim efficiency.
	*
	* If @tree is not set, reclaim efficiency is recorded for @memcg, and
	* only in-kernel users are notified.
	*
	* This function does not return any value.
	*/
	void vmpressure(gfp_t gfp, struct mem_cgroup *memcg, bool tree,
	unsigned long scanned, unsigned long reclaimed)
	{
	if (!memcg)
	vmpressure_global(gfp, scanned, reclaimed);

	if (IS_ENABLED(CONFIG_MEMCG))
	vmpressure_memcg(gfp, memcg, tree, scanned, reclaimed);
	}

	/**
	* vmpressure_prio() - Account memory pressure through reclaimer priority level
	* @gfp: reclaimer's gfp mask
	* @memcg: cgroup memory controller handle
	* @prio: reclaimer's priority
	*
	* This function should be called from the reclaim path every time when
	* the vmscan's reclaiming priority (scanning depth) changes.
	*
	* This function does not return any value.
	*/
	void vmpressure_prio(gfp_t gfp, struct mem_cgroup *memcg, int prio)
	{
	/*
	* We only use prio for accounting critical level. For more info
	* see comment for vmpressure_level_critical_prio variable above.
	*/
	if (prio > vmpressure_level_critical_prio)
	return;

	/*
	* OK, the prio is below the threshold, updating vmpressure
	* information before shrinker dives into long shrinking of long
	* range vmscan. Passing scanned = vmpressure_win, reclaimed = 0
	* to the vmpressure() basically means that we signal 'critical'
	* level.
	*/
	vmpressure(gfp, memcg, true, vmpressure_win, 0);
	}

	/**
	* vmpressure_register_event() - Bind vmpressure notifications to an eventfd
	* @memcg: memcg that is interested in vmpressure notifications
	* @eventfd: eventfd context to link notifications with
	* @args: event arguments (used to set up a pressure level threshold)
	*
	* This function associates eventfd context with the vmpressure
	* infrastructure, so that the notifications will be delivered to the
	* @eventfd. The @args parameter is a string that denotes pressure level
	* threshold (one of vmpressure_str_levels, i.e. "low", "medium", or
	* "critical").
	*
	* To be used as memcg event method.
	*/
	int vmpressure_register_event(struct mem_cgroup *memcg,
	struct eventfd_ctx eventfd, const char args)
	{
	struct vmpressure *vmpr = memcg_to_vmpressure(memcg);
	struct vmpressure_event *ev;
	int level;

	for (level = 0; level < VMPRESSURE_NUM_LEVELS; level++) {
	if (!strcmp(vmpressure_str_levels[level], args))
	break;
	}

	if (level >= VMPRESSURE_NUM_LEVELS)
	return -EINVAL;

	ev = kzalloc(sizeof(*ev), GFP_KERNEL);
	if (!ev)
	return -ENOMEM;

	ev->efd = eventfd;
	ev->level = level;

	mutex_lock(&vmpr->events_lock);
	list_add(&ev->node, &vmpr->events);
	mutex_unlock(&vmpr->events_lock);

	return 0;
	}

	/**
	* vmpressure_unregister_event() - Unbind eventfd from vmpressure
	* @memcg: memcg handle
	* @eventfd: eventfd context that was used to link vmpressure with the @cg
	*
	* This function does internal manipulations to detach the @eventfd from
	* the vmpressure notifications, and then frees internal resources
	* associated with the @eventfd (but the @eventfd itself is not freed).
	*
	* To be used as memcg event method.
	*/
	void vmpressure_unregister_event(struct mem_cgroup *memcg,
	struct eventfd_ctx *eventfd)
	{
	struct vmpressure *vmpr = memcg_to_vmpressure(memcg);
	struct vmpressure_event *ev;

	mutex_lock(&vmpr->events_lock);
	list_for_each_entry(ev, &vmpr->events, node) {
	if (ev->efd != eventfd)
	continue;
	list_del(&ev->node);
	kfree(ev);
	break;
	}
	mutex_unlock(&vmpr->events_lock);
	}

	/**
	* vmpressure_init() - Initialize vmpressure control structure
	* @vmpr: Structure to be initialized
	*
	* This function should be called on every allocated vmpressure structure
	* before any usage.
	*/
	void vmpressure_init(struct vmpressure *vmpr)
	{
	spin_lock_init(&vmpr->sr_lock);
	mutex_init(&vmpr->events_lock);
	INIT_LIST_HEAD(&vmpr->events);
	INIT_WORK(&vmpr->work, vmpressure_work_fn);
	}

	/**
	* vmpressure_cleanup() - shuts down vmpressure control structure
	* @vmpr: Structure to be cleaned up
	*
	* This function should be called before the structure in which it is
	* embedded is cleaned up.
	*/
	void vmpressure_cleanup(struct vmpressure *vmpr)
	{
	/*
	* Make sure there is no pending work before eventfd infrastructure
	* goes away.
	*/
	flush_work(&vmpr->work);
	}

	static int vmpressure_global_init(void)
	{
	vmpressure_init(&global_vmpressure);
	return 0;
	}
	late_initcall(vmpressure_global_init);