@@ -40,6 +40,7 @@ Features:
- soft limit
- moving (recharging) account at moving a task is selectable.
- usage threshold notifier
+ - memory pressure notifier
- oom-killer disable knob and oom-notifier
- Root cgroup has no limit controls.
@@ -65,6 +66,7 @@ Brief summary of control files.
memory.stat # show various statistics
memory.use_hierarchy # set/show hierarchical account enabled
memory.force_empty # trigger forced move charge to parent
+ memory.pressure_level # set memory pressure notifications
memory.swappiness # set/show swappiness parameter of vmscan
(See sysctl's vm.swappiness)
memory.move_charge_at_immigrate # set/show controls of moving charges
@@ -778,7 +780,73 @@ At reading, current status of OOM is shown.
under_oom 0 or 1 (if 1, the memory cgroup is under OOM, tasks may
be stopped.)
-11. TODO
+11. Memory Pressure
+
+The pressure level notifications can be used to monitor the memory
+allocation cost; based on the pressure, applications can implement
+different strategies of managing their memory resources. The pressure
+levels are defined as following:
+
+The "low" level means that the system is reclaiming memory for new
+allocations. Monitoring this reclaiming activity might be useful for
+maintaining cache level. Upon notification, the program (typically
+"Activity Manager") might analyze vmstat and act in advance (i.e.
+prematurely shutdown unimportant services).
+
+The "medium" level means that the system is experiencing medium memory
+pressure, the system might be making swap, paging out active file caches,
+etc. Upon this event applications may decide to further analyze
+vmstat/zoneinfo/memcg or internal memory usage statistics and free any
+resources that can be easily reconstructed or re-read from a disk.
+
+The "critical" level means that the system is actively thrashing, it is
+about to out of memory (OOM) or even the in-kernel OOM killer is on its
+way to trigger. Applications should do whatever they can to help the
+system. It might be too late to consult with vmstat or any other
+statistics, so it's advisable to take an immediate action.
+
+The events are propagated upward until the event is handled, i.e. the
+events are not pass-through. Here is what this means: for example you have
+three cgroups: A->B->C. Now you set up an event listener on cgroups A, B
+and C, and suppose group C experiences some pressure. In this situation,
+only group C will receive the notification, i.e. groups A and B will not
+receive it. This is done to avoid excessive "broadcasting" of messages,
+which disturbs the system and which is especially bad if we are low on
+memory or thrashing. So, organize the cgroups wisely, or propagate the
+events manually (or, ask us to implement the pass-through events,
+explaining why would you need them.)
+
+The file memory.pressure_level is only used to setup an eventfd. To
+register a notification, an application must:
+
+- create an eventfd using eventfd(2);
+- open memory.pressure_level;
+- write string like "<event_fd> <fd of memory.pressure_level> <level>"
+ to cgroup.event_control.
+
+Application will be notified through eventfd when memory pressure is at
+the specific level (or higher). Read/write operations to
+memory.pressure_level are no implemented.
+
+Test:
+
+ Here is a small script example that makes a new cgroup, sets up a
+ memory limit, sets up a notification in the cgroup and then makes child
+ cgroup experience a critical pressure:
+
+ # cd /sys/fs/cgroup/memory/
+ # mkdir foo
+ # cd foo
+ # cgroup_event_listener memory.pressure_level low &
+ # echo 8000000 > memory.limit_in_bytes
+ # echo 8000000 > memory.memsw.limit_in_bytes
+ # echo $$ > tasks
+ # dd if=/dev/zero | read x
+
+ (Expect a bunch of notifications, and eventually, the oom-killer will
+ trigger.)
+
+12. TODO
1. Add support for accounting huge pages (as a separate controller)
2. Make per-cgroup scanner reclaim not-shared pages first
new file mode 100644
@@ -0,0 +1,48 @@
+#ifndef __LINUX_VMPRESSURE_H
+#define __LINUX_VMPRESSURE_H
+
+#include <linux/mutex.h>
+#include <linux/list.h>
+#include <linux/workqueue.h>
+#include <linux/gfp.h>
+#include <linux/types.h>
+#include <linux/cgroup.h>
+
+struct vmpressure {
+ unsigned long scanned;
+ unsigned long reclaimed;
+ /* The lock is used to keep the scanned/reclaimed above in sync. */
+ struct mutex sr_lock;
+
+ /* The list of vmpressure_event structs. */
+ struct list_head events;
+ /* Have to grab the lock on events traversal or modifications. */
+ struct mutex events_lock;
+
+ struct work_struct work;
+};
+
+struct mem_cgroup;
+
+#ifdef CONFIG_MEMCG
+extern void vmpressure(gfp_t gfp, struct mem_cgroup *memcg,
+ unsigned long scanned, unsigned long reclaimed);
+extern void vmpressure_prio(gfp_t gfp, struct mem_cgroup *memcg, int prio);
+#else
+static inline void vmpressure(gfp_t gfp, struct mem_cgroup *memcg,
+ unsigned long scanned, unsigned long reclaimed) {}
+static inline void vmpressure_prio(gfp_t gfp, struct mem_cgroup *memcg,
+ int prio) {}
+#endif /* CONFIG_MEMCG */
+
+extern void vmpressure_init(struct vmpressure *vmpr);
+extern struct vmpressure *memcg_to_vmpressure(struct mem_cgroup *memcg);
+extern struct cgroup_subsys_state *vmpressure_to_css(struct vmpressure *vmpr);
+extern struct vmpressure *css_to_vmpressure(struct cgroup_subsys_state *css);
+extern int vmpressure_register_event(struct cgroup *cg, struct cftype *cft,
+ struct eventfd_ctx *eventfd,
+ const char *args);
+extern void vmpressure_unregister_event(struct cgroup *cg, struct cftype *cft,
+ struct eventfd_ctx *eventfd);
+
+#endif /* __LINUX_VMPRESSURE_H */
@@ -50,7 +50,7 @@ obj-$(CONFIG_FS_XIP) += filemap_xip.o
obj-$(CONFIG_MIGRATION) += migrate.o
obj-$(CONFIG_QUICKLIST) += quicklist.o
obj-$(CONFIG_TRANSPARENT_HUGEPAGE) += huge_memory.o
-obj-$(CONFIG_MEMCG) += memcontrol.o page_cgroup.o
+obj-$(CONFIG_MEMCG) += memcontrol.o page_cgroup.o vmpressure.o
obj-$(CONFIG_CGROUP_HUGETLB) += hugetlb_cgroup.o
obj-$(CONFIG_MEMORY_FAILURE) += memory-failure.o
obj-$(CONFIG_HWPOISON_INJECT) += hwpoison-inject.o
@@ -49,6 +49,7 @@
#include <linux/fs.h>
#include <linux/seq_file.h>
#include <linux/vmalloc.h>
+#include <linux/vmpressure.h>
#include <linux/mm_inline.h>
#include <linux/page_cgroup.h>
#include <linux/cpu.h>
@@ -315,6 +316,9 @@ struct mem_cgroup {
/* thresholds for mem+swap usage. RCU-protected */
struct mem_cgroup_thresholds memsw_thresholds;
+ /* vmpressure notifications */
+ struct vmpressure vmpressure;
+
union {
/* For oom notifier event fd */
struct list_head oom_notify;
@@ -376,6 +380,7 @@ struct mem_cgroup {
atomic_t numainfo_events;
atomic_t numainfo_updating;
#endif
+
/*
* Per cgroup active and inactive list, similar to the
* per zone LRU lists.
@@ -576,6 +581,24 @@ struct mem_cgroup *mem_cgroup_from_css(struct cgroup_subsys_state *s)
return container_of(s, struct mem_cgroup, css);
}
+/* Some nice accessors for the vmpressure. */
+struct vmpressure *memcg_to_vmpressure(struct mem_cgroup *memcg)
+{
+ if (!memcg)
+ memcg = root_mem_cgroup;
+ return &memcg->vmpressure;
+}
+
+struct cgroup_subsys_state *vmpressure_to_css(struct vmpressure *vmpr)
+{
+ return &container_of(vmpr, struct mem_cgroup, vmpressure)->css;
+}
+
+struct vmpressure *css_to_vmpressure(struct cgroup_subsys_state *css)
+{
+ return &mem_cgroup_from_css(css)->vmpressure;
+}
+
static inline bool mem_cgroup_is_root(struct mem_cgroup *memcg)
{
return (memcg == root_mem_cgroup);
@@ -6074,6 +6097,11 @@ static struct cftype mem_cgroup_files[] = {
.unregister_event = mem_cgroup_oom_unregister_event,
.private = MEMFILE_PRIVATE(_OOM_TYPE, OOM_CONTROL),
},
+ {
+ .name = "pressure_level",
+ .register_event = vmpressure_register_event,
+ .unregister_event = vmpressure_unregister_event,
+ },
#ifdef CONFIG_NUMA
{
.name = "numa_stat",
@@ -6365,6 +6393,7 @@ mem_cgroup_css_alloc(struct cgroup *cont)
memcg->move_charge_at_immigrate = 0;
mutex_init(&memcg->thresholds_lock);
spin_lock_init(&memcg->move_lock);
+ vmpressure_init(&memcg->vmpressure);
return &memcg->css;
new file mode 100644
@@ -0,0 +1,374 @@
+/*
+ * 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 *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);
+}
@@ -19,6 +19,7 @@
#include <linux/pagemap.h>
#include <linux/init.h>
#include <linux/highmem.h>
+#include <linux/vmpressure.h>
#include <linux/vmstat.h>
#include <linux/file.h>
#include <linux/writeback.h>
@@ -1982,6 +1983,11 @@ static void shrink_zone(struct zone *zone, struct scan_control *sc)
}
memcg = mem_cgroup_iter(root, memcg, &reclaim);
} while (memcg);
+
+ vmpressure(sc->gfp_mask, sc->target_mem_cgroup,
+ sc->nr_scanned - nr_scanned,
+ sc->nr_reclaimed - nr_reclaimed);
+
} while (should_continue_reclaim(zone, sc->nr_reclaimed - nr_reclaimed,
sc->nr_scanned - nr_scanned, sc));
}
@@ -2167,6 +2173,8 @@ static unsigned long do_try_to_free_pages(struct zonelist *zonelist,
count_vm_event(ALLOCSTALL);
do {
+ vmpressure_prio(sc->gfp_mask, sc->target_mem_cgroup,
+ sc->priority);
sc->nr_scanned = 0;
aborted_reclaim = shrink_zones(zonelist, sc);