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@@ -0,0 +1,374 @@
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+/*
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+ * Linux VM pressure
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+ *
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+ * Copyright 2012 Linaro Ltd.
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+ * Anton Vorontsov <anton.vorontsov@linaro.org>
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+ *
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+ * Based on ideas from Andrew Morton, David Rientjes, KOSAKI Motohiro,
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+ * Leonid Moiseichuk, Mel Gorman, Minchan Kim and Pekka Enberg.
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+ *
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+ * This program is free software; you can redistribute it and/or modify it
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+ * under the terms of the GNU General Public License version 2 as published
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+ * by the Free Software Foundation.
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+ */
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+
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+#include <linux/cgroup.h>
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+#include <linux/fs.h>
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+#include <linux/log2.h>
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+#include <linux/sched.h>
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+#include <linux/mm.h>
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+#include <linux/vmstat.h>
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+#include <linux/eventfd.h>
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+#include <linux/swap.h>
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+#include <linux/printk.h>
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+#include <linux/vmpressure.h>
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+
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+/*
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+ * The window size (vmpressure_win) is the number of scanned pages before
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+ * we try to analyze scanned/reclaimed ratio. So the window is used as a
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+ * rate-limit tunable for the "low" level notification, and also for
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+ * averaging the ratio for medium/critical levels. Using small window
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+ * sizes can cause lot of false positives, but too big window size will
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+ * delay the notifications.
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+ *
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+ * As the vmscan reclaimer logic works with chunks which are multiple of
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+ * SWAP_CLUSTER_MAX, it makes sense to use it for the window size as well.
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+ *
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+ * TODO: Make the window size depend on machine size, as we do for vmstat
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+ * thresholds. Currently we set it to 512 pages (2MB for 4KB pages).
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+ */
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+static const unsigned long vmpressure_win = SWAP_CLUSTER_MAX * 16;
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+
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+/*
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+ * These thresholds are used when we account memory pressure through
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+ * scanned/reclaimed ratio. The current values were chosen empirically. In
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+ * essence, they are percents: the higher the value, the more number
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+ * unsuccessful reclaims there were.
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+ */
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+static const unsigned int vmpressure_level_med = 60;
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+static const unsigned int vmpressure_level_critical = 95;
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+
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+/*
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+ * When there are too little pages left to scan, vmpressure() may miss the
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+ * critical pressure as number of pages will be less than "window size".
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+ * However, in that case the vmscan priority will raise fast as the
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+ * reclaimer will try to scan LRUs more deeply.
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+ *
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+ * The vmscan logic considers these special priorities:
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+ *
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+ * prio == DEF_PRIORITY (12): reclaimer starts with that value
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+ * prio <= DEF_PRIORITY - 2 : kswapd becomes somewhat overwhelmed
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+ * prio == 0 : close to OOM, kernel scans every page in an lru
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+ *
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+ * Any value in this range is acceptable for this tunable (i.e. from 12 to
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+ * 0). Current value for the vmpressure_level_critical_prio is chosen
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+ * empirically, but the number, in essence, means that we consider
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+ * critical level when scanning depth is ~10% of the lru size (vmscan
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+ * scans 'lru_size >> prio' pages, so it is actually 12.5%, or one
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+ * eights).
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+ */
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+static const unsigned int vmpressure_level_critical_prio = ilog2(100 / 10);
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+
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+static struct vmpressure *work_to_vmpressure(struct work_struct *work)
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+{
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+ return container_of(work, struct vmpressure, work);
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+}
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+
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+static struct vmpressure *cg_to_vmpressure(struct cgroup *cg)
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+{
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+ return css_to_vmpressure(cgroup_subsys_state(cg, mem_cgroup_subsys_id));
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+}
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+
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+static struct vmpressure *vmpressure_parent(struct vmpressure *vmpr)
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+{
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+ struct cgroup *cg = vmpressure_to_css(vmpr)->cgroup;
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+ struct mem_cgroup *memcg = mem_cgroup_from_cont(cg);
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+
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+ memcg = parent_mem_cgroup(memcg);
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+ if (!memcg)
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+ return NULL;
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+ return memcg_to_vmpressure(memcg);
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+}
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+
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+enum vmpressure_levels {
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+ VMPRESSURE_LOW = 0,
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+ VMPRESSURE_MEDIUM,
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+ VMPRESSURE_CRITICAL,
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+ VMPRESSURE_NUM_LEVELS,
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+};
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+
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+static const char * const vmpressure_str_levels[] = {
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+ [VMPRESSURE_LOW] = "low",
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+ [VMPRESSURE_MEDIUM] = "medium",
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+ [VMPRESSURE_CRITICAL] = "critical",
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+};
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+
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+static enum vmpressure_levels vmpressure_level(unsigned long pressure)
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+{
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+ if (pressure >= vmpressure_level_critical)
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+ return VMPRESSURE_CRITICAL;
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+ else if (pressure >= vmpressure_level_med)
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+ return VMPRESSURE_MEDIUM;
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+ return VMPRESSURE_LOW;
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+}
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+
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+static enum vmpressure_levels vmpressure_calc_level(unsigned long scanned,
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+ unsigned long reclaimed)
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+{
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+ unsigned long scale = scanned + reclaimed;
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+ unsigned long pressure;
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+
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+ /*
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+ * We calculate the ratio (in percents) of how many pages were
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+ * scanned vs. reclaimed in a given time frame (window). Note that
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+ * time is in VM reclaimer's "ticks", i.e. number of pages
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+ * scanned. This makes it possible to set desired reaction time
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+ * and serves as a ratelimit.
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+ */
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+ pressure = scale - (reclaimed * scale / scanned);
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+ pressure = pressure * 100 / scale;
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+
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+ pr_debug("%s: %3lu (s: %lu r: %lu)\n", __func__, pressure,
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+ scanned, reclaimed);
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+
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+ return vmpressure_level(pressure);
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+}
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+
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+struct vmpressure_event {
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+ struct eventfd_ctx *efd;
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+ enum vmpressure_levels level;
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+ struct list_head node;
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+};
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+
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+static bool vmpressure_event(struct vmpressure *vmpr,
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+ unsigned long scanned, unsigned long reclaimed)
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+{
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+ struct vmpressure_event *ev;
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+ enum vmpressure_levels level;
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+ bool signalled = false;
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+
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+ level = vmpressure_calc_level(scanned, reclaimed);
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+
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+ mutex_lock(&vmpr->events_lock);
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+
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+ list_for_each_entry(ev, &vmpr->events, node) {
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+ if (level >= ev->level) {
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+ eventfd_signal(ev->efd, 1);
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+ signalled = true;
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+ }
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+ }
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+
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+ mutex_unlock(&vmpr->events_lock);
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+
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+ return signalled;
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+}
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+
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+static void vmpressure_work_fn(struct work_struct *work)
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+{
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+ struct vmpressure *vmpr = work_to_vmpressure(work);
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+ unsigned long scanned;
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+ unsigned long reclaimed;
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+
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+ /*
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+ * Several contexts might be calling vmpressure(), so it is
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+ * possible that the work was rescheduled again before the old
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+ * work context cleared the counters. In that case we will run
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+ * just after the old work returns, but then scanned might be zero
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+ * here. No need for any locks here since we don't care if
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+ * vmpr->reclaimed is in sync.
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+ */
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+ if (!vmpr->scanned)
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+ return;
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+
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+ mutex_lock(&vmpr->sr_lock);
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+ scanned = vmpr->scanned;
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+ reclaimed = vmpr->reclaimed;
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+ vmpr->scanned = 0;
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+ vmpr->reclaimed = 0;
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+ mutex_unlock(&vmpr->sr_lock);
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+
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+ do {
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+ if (vmpressure_event(vmpr, scanned, reclaimed))
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+ break;
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+ /*
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+ * If not handled, propagate the event upward into the
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+ * hierarchy.
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+ */
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+ } while ((vmpr = vmpressure_parent(vmpr)));
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+}
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+
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+/**
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+ * vmpressure() - Account memory pressure through scanned/reclaimed ratio
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+ * @gfp: reclaimer's gfp mask
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+ * @memcg: cgroup memory controller handle
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+ * @scanned: number of pages scanned
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+ * @reclaimed: number of pages reclaimed
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+ *
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+ * This function should be called from the vmscan reclaim path to account
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+ * "instantaneous" memory pressure (scanned/reclaimed ratio). The raw
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+ * pressure index is then further refined and averaged over time.
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+ *
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+ * This function does not return any value.
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+ */
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+void vmpressure(gfp_t gfp, struct mem_cgroup *memcg,
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+ unsigned long scanned, unsigned long reclaimed)
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+{
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+ struct vmpressure *vmpr = memcg_to_vmpressure(memcg);
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+
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+ /*
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+ * Here we only want to account pressure that userland is able to
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+ * help us with. For example, suppose that DMA zone is under
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+ * pressure; if we notify userland about that kind of pressure,
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+ * then it will be mostly a waste as it will trigger unnecessary
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+ * freeing of memory by userland (since userland is more likely to
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+ * have HIGHMEM/MOVABLE pages instead of the DMA fallback). That
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+ * is why we include only movable, highmem and FS/IO pages.
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+ * Indirect reclaim (kswapd) sets sc->gfp_mask to GFP_KERNEL, so
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+ * we account it too.
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+ */
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+ if (!(gfp & (__GFP_HIGHMEM | __GFP_MOVABLE | __GFP_IO | __GFP_FS)))
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+ return;
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+
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+ /*
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+ * If we got here with no pages scanned, then that is an indicator
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+ * that reclaimer was unable to find any shrinkable LRUs at the
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+ * current scanning depth. But it does not mean that we should
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+ * report the critical pressure, yet. If the scanning priority
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+ * (scanning depth) goes too high (deep), we will be notified
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+ * through vmpressure_prio(). But so far, keep calm.
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+ */
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+ if (!scanned)
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+ return;
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+
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+ mutex_lock(&vmpr->sr_lock);
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+ vmpr->scanned += scanned;
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+ vmpr->reclaimed += reclaimed;
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+ scanned = vmpr->scanned;
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+ mutex_unlock(&vmpr->sr_lock);
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+
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+ if (scanned < vmpressure_win || work_pending(&vmpr->work))
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+ return;
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+ schedule_work(&vmpr->work);
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+}
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+
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+/**
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+ * vmpressure_prio() - Account memory pressure through reclaimer priority level
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+ * @gfp: reclaimer's gfp mask
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+ * @memcg: cgroup memory controller handle
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+ * @prio: reclaimer's priority
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+ *
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+ * This function should be called from the reclaim path every time when
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+ * the vmscan's reclaiming priority (scanning depth) changes.
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+ *
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+ * This function does not return any value.
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+ */
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+void vmpressure_prio(gfp_t gfp, struct mem_cgroup *memcg, int prio)
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+{
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+ /*
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+ * We only use prio for accounting critical level. For more info
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+ * see comment for vmpressure_level_critical_prio variable above.
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+ */
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+ if (prio > vmpressure_level_critical_prio)
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+ return;
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+
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+ /*
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+ * OK, the prio is below the threshold, updating vmpressure
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+ * information before shrinker dives into long shrinking of long
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+ * range vmscan. Passing scanned = vmpressure_win, reclaimed = 0
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+ * to the vmpressure() basically means that we signal 'critical'
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+ * level.
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+ */
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+ vmpressure(gfp, memcg, vmpressure_win, 0);
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+}
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+
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+/**
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+ * vmpressure_register_event() - Bind vmpressure notifications to an eventfd
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+ * @cg: cgroup that is interested in vmpressure notifications
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+ * @cft: cgroup control files handle
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+ * @eventfd: eventfd context to link notifications with
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+ * @args: event arguments (used to set up a pressure level threshold)
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+ *
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+ * This function associates eventfd context with the vmpressure
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+ * infrastructure, so that the notifications will be delivered to the
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+ * @eventfd. The @args parameter is a string that denotes pressure level
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+ * threshold (one of vmpressure_str_levels, i.e. "low", "medium", or
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+ * "critical").
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+ *
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+ * This function should not be used directly, just pass it to (struct
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+ * cftype).register_event, and then cgroup core will handle everything by
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+ * itself.
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+ */
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+int vmpressure_register_event(struct cgroup *cg, struct cftype *cft,
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+ struct eventfd_ctx *eventfd, const char *args)
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+{
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+ struct vmpressure *vmpr = cg_to_vmpressure(cg);
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+ struct vmpressure_event *ev;
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+ int level;
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+
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+ for (level = 0; level < VMPRESSURE_NUM_LEVELS; level++) {
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+ if (!strcmp(vmpressure_str_levels[level], args))
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+ break;
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+ }
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+
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+ if (level >= VMPRESSURE_NUM_LEVELS)
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+ return -EINVAL;
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+
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+ ev = kzalloc(sizeof(*ev), GFP_KERNEL);
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+ if (!ev)
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+ return -ENOMEM;
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+
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+ ev->efd = eventfd;
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+ ev->level = level;
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+
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+ mutex_lock(&vmpr->events_lock);
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+ list_add(&ev->node, &vmpr->events);
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+ mutex_unlock(&vmpr->events_lock);
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+
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+ return 0;
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+}
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+
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+/**
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+ * vmpressure_unregister_event() - Unbind eventfd from vmpressure
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+ * @cg: cgroup handle
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+ * @cft: cgroup control files handle
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+ * @eventfd: eventfd context that was used to link vmpressure with the @cg
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+ *
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+ * This function does internal manipulations to detach the @eventfd from
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+ * the vmpressure notifications, and then frees internal resources
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+ * associated with the @eventfd (but the @eventfd itself is not freed).
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+ *
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+ * This function should not be used directly, just pass it to (struct
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+ * cftype).unregister_event, and then cgroup core will handle everything
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+ * by itself.
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+ */
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+void vmpressure_unregister_event(struct cgroup *cg, struct cftype *cft,
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+ struct eventfd_ctx *eventfd)
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+{
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+ struct vmpressure *vmpr = cg_to_vmpressure(cg);
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+ struct vmpressure_event *ev;
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+
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+ mutex_lock(&vmpr->events_lock);
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+ list_for_each_entry(ev, &vmpr->events, node) {
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+ if (ev->efd != eventfd)
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+ continue;
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+ list_del(&ev->node);
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+ kfree(ev);
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+ break;
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+ }
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+ mutex_unlock(&vmpr->events_lock);
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+}
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+
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+/**
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+ * vmpressure_init() - Initialize vmpressure control structure
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+ * @vmpr: Structure to be initialized
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+ *
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+ * This function should be called on every allocated vmpressure structure
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+ * before any usage.
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+ */
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+void vmpressure_init(struct vmpressure *vmpr)
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+{
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+ mutex_init(&vmpr->sr_lock);
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+ mutex_init(&vmpr->events_lock);
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+ INIT_LIST_HEAD(&vmpr->events);
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+ INIT_WORK(&vmpr->work, vmpressure_work_fn);
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+}
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Anton Vorontsov