1 files changed, 374 insertions, 0 deletions
diff --git a/mm/vmpressure.c b/mm/vmpressure.c
new file mode 100644
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--- /dev/null
+++ b/mm/vmpressure.c
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+/*
+ * 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/swap.h>
+#include <linux/printk.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;
+
+/*
+ * 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);
+}
+
+static struct vmpressure *cg_to_vmpressure(struct cgroup *cg)
+{
+	return css_to_vmpressure(cgroup_subsys_state(cg, mem_cgroup_subsys_id));
+}
+
+static struct vmpressure *vmpressure_parent(struct vmpressure *vmpr)
+{
+	struct cgroup *cg = vmpressure_to_css(vmpr)->cgroup;
+	struct mem_cgroup *memcg = mem_cgroup_from_cont(cg);
+
+	memcg = parent_mem_cgroup(memcg);
+	if (!memcg)
+		return NULL;
+	return memcg_to_vmpressure(memcg);
+}
+
+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 enum vmpressure_levels vmpressure_calc_level(unsigned long scanned,
+						    unsigned long reclaimed)
+{
+	unsigned long scale = scanned + reclaimed;
+	unsigned long pressure;
+
+	/*
+	 * 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;
+
+	pr_debug("%s: %3lu  (s: %lu  r: %lu)\n", __func__, pressure,
+		 scanned, reclaimed);
+
+	return vmpressure_level(pressure);
+}
+
+struct vmpressure_event {
+	struct eventfd_ctx *efd;
+	enum vmpressure_levels level;
+	struct list_head node;
+};
+
+static bool vmpressure_event(struct vmpressure *vmpr,
+			     unsigned long scanned, unsigned long reclaimed)
+{
+	struct vmpressure_event *ev;
+	enum vmpressure_levels level;
+	bool signalled = false;
+
+	level = vmpressure_calc_level(scanned, reclaimed);
+
+	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;
+
+	/*
+	 * 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.
+	 */
+	if (!vmpr->scanned)
+		return;
+
+	mutex_lock(&vmpr->sr_lock);
+	scanned = vmpr->scanned;
+	reclaimed = vmpr->reclaimed;
+	vmpr->scanned = 0;
+	vmpr->reclaimed = 0;
+	mutex_unlock(&vmpr->sr_lock);
+
+	do {
+		if (vmpressure_event(vmpr, scanned, reclaimed))
+			break;
+		/*
+		 * If not handled, propagate the event upward into the
+		 * hierarchy.
+		 */
+	} while ((vmpr = vmpressure_parent(vmpr)));
+}
+
+/**
+ * vmpressure() - Account memory pressure through scanned/reclaimed ratio
+ * @gfp:	reclaimer's gfp mask
+ * @memcg:	cgroup memory controller handle
+ * @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.
+ *
+ * This function does not return any value.
+ */
+void vmpressure(gfp_t gfp, struct mem_cgroup *memcg,
+		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;
+
+	mutex_lock(&vmpr->sr_lock);
+	vmpr->scanned += scanned;
+	vmpr->reclaimed += reclaimed;
+	scanned = vmpr->scanned;
+	mutex_unlock(&vmpr->sr_lock);
+
+	if (scanned < vmpressure_win || work_pending(&vmpr->work))
+		return;
+	schedule_work(&vmpr->work);
+}
+
+/**
+ * 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, vmpressure_win, 0);
+}
+
+/**
+ * vmpressure_register_event() - Bind vmpressure notifications to an eventfd
+ * @cg:		cgroup that is interested in vmpressure notifications
+ * @cft:	cgroup control files handle
+ * @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").
+ *
+ * This function should not be used directly, just pass it to (struct
+ * cftype).register_event, and then cgroup core will handle everything by
+ * itself.
+ */
+int vmpressure_register_event(struct cgroup *cg, struct cftype *cft,
+			      struct eventfd_ctx *eventfd, const char *args)
+{
+	struct vmpressure *vmpr = cg_to_vmpressure(cg);
+	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
+ * @cg:		cgroup handle
+ * @cft:	cgroup control files 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).
+ *
+ * This function should not be used directly, just pass it to (struct
+ * cftype).unregister_event, and then cgroup core will handle everything
+ * by itself.
+ */
+void vmpressure_unregister_event(struct cgroup *cg, struct cftype *cft,
+				 struct eventfd_ctx *eventfd)
+{
+	struct vmpressure *vmpr = cg_to_vmpressure(cg);
+	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)
+{
+	mutex_init(&vmpr->sr_lock);
+	mutex_init(&vmpr->events_lock);
+	INIT_LIST_HEAD(&vmpr->events);
+	INIT_WORK(&vmpr->work, vmpressure_work_fn);
+}