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Subject[PATCH 1/2] Add mempressure cgroup
Date
This commit implements David Rientjes' idea of mempressure cgroup.

The main characteristics are the same to what I've tried to add to vmevent
API; internally, it uses Mel Gorman's idea of scanned/reclaimed ratio for
pressure index calculation. But we don't expose the index to the userland.
Instead, there are three levels of the pressure:

o low (just reclaiming, e.g. caches are draining);
o medium (allocation cost becomes high, e.g. swapping);
o oom (about to oom very soon).

The rationale behind exposing levels and not the raw pressure index
described here: http://lkml.org/lkml/2012/11/16/675

For a task it is possible to be in both cpusets, memcg and mempressure
cgroups, so by rearranging the tasks it is possible to watch a specific
pressure (i.e. caused by cpuset and/or memcg).

Note that while this adds the cgroups support, the code is well separated
and eventually we might add a lightweight, non-cgroups API, i.e. vmevent.
But this is another story.

Signed-off-by: Anton Vorontsov <anton.vorontsov@linaro.org>
---
Documentation/cgroups/mempressure.txt | 50 ++++++
include/linux/cgroup_subsys.h | 6 +
include/linux/vmstat.h | 11 ++
init/Kconfig | 12 ++
mm/Makefile | 1 +
mm/mempressure.c | 330 ++++++++++++++++++++++++++++++++++
mm/vmscan.c | 4 +
7 files changed, 414 insertions(+)
create mode 100644 Documentation/cgroups/mempressure.txt
create mode 100644 mm/mempressure.c

diff --git a/Documentation/cgroups/mempressure.txt b/Documentation/cgroups/mempressure.txt
new file mode 100644
index 0000000..dbc0aca
--- /dev/null
+++ b/Documentation/cgroups/mempressure.txt
@@ -0,0 +1,50 @@
+ Memory pressure cgroup
+~~~~~~~~~~~~~~~~~~~~~~~~~~
+ Before using the mempressure cgroup, make sure you have it mounted:
+
+ # cd /sys/fs/cgroup/
+ # mkdir mempressure
+ # mount -t cgroup cgroup ./mempressure -o mempressure
+
+ It is possible to combine cgroups, for example you can mount memory
+ (memcg) and mempressure cgroups together:
+
+ # mount -t cgroup cgroup ./mempressure -o memory,mempressure
+
+ That way the reported pressure will honour memory cgroup limits. The
+ same goes for cpusets.
+
+ After the hierarchy is mounted, you can use the following API:
+
+ /sys/fs/cgroup/.../mempressure.level
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ To maintain the interactivity/memory allocation cost, one can use the
+ pressure level notifications, and the levels are defined like this:
+
+ The "low" level means that the system is reclaiming memory for new
+ allocations. Monitoring reclaiming activity might be useful for
+ maintaining overall system's 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, there is some mild swapping activity. Upon this event
+ applications may decide to free any resources that can be easily
+ reconstructed or re-read from a disk.
+
+ The "oom" 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.
+
+ Event control:
+ Is used to setup an eventfd with a level threshold. The argument to
+ the event control specifies the level threshold.
+ Read:
+ Reads mempory presure levels: low, medium or oom.
+ Write:
+ Not implemented.
+ Test:
+ To set up a notification:
+
+ # cgroup_event_listener ./mempressure.level low
+ ("low", "medium", "oom" are permitted.)
diff --git a/include/linux/cgroup_subsys.h b/include/linux/cgroup_subsys.h
index f204a7a..b9802e2 100644
--- a/include/linux/cgroup_subsys.h
+++ b/include/linux/cgroup_subsys.h
@@ -37,6 +37,12 @@ SUBSYS(mem_cgroup)

/* */

+#if IS_SUBSYS_ENABLED(CONFIG_CGROUP_MEMPRESSURE)
+SUBSYS(mpc_cgroup)
+#endif
+
+/* */
+
#if IS_SUBSYS_ENABLED(CONFIG_CGROUP_DEVICE)
SUBSYS(devices)
#endif
diff --git a/include/linux/vmstat.h b/include/linux/vmstat.h
index a13291f..c1a66c7 100644
--- a/include/linux/vmstat.h
+++ b/include/linux/vmstat.h
@@ -10,6 +10,17 @@

extern int sysctl_stat_interval;

+struct mem_cgroup;
+#ifdef CONFIG_CGROUP_MEMPRESSURE
+extern void vmpressure(struct mem_cgroup *memcg,
+ ulong scanned, ulong reclaimed);
+extern void vmpressure_prio(struct mem_cgroup *memcg, int prio);
+#else
+static inline void vmpressure(struct mem_cgroup *memcg,
+ ulong scanned, ulong reclaimed) {}
+static inline void vmpressure_prio(struct mem_cgroup *memcg, int prio) {}
+#endif
+
#ifdef CONFIG_VM_EVENT_COUNTERS
/*
* Light weight per cpu counter implementation.
diff --git a/init/Kconfig b/init/Kconfig
index 7d30240..d526249 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -891,6 +891,18 @@ config MEMCG_KMEM
the kmem extension can use it to guarantee that no group of processes
will ever exhaust kernel resources alone.

+config CGROUP_MEMPRESSURE
+ bool "Memory pressure monitor for Control Groups"
+ help
+ The memory pressure monitor cgroup provides a facility for
+ userland programs so that they could easily assist the kernel
+ with the memory management. So far the API provides simple,
+ levels-based memory pressure notifications.
+
+ For more information see Documentation/cgroups/mempressure.txt
+
+ If unsure, say N.
+
config CGROUP_HUGETLB
bool "HugeTLB Resource Controller for Control Groups"
depends on RESOURCE_COUNTERS && HUGETLB_PAGE && EXPERIMENTAL
diff --git a/mm/Makefile b/mm/Makefile
index 3a46287..e69bbda 100644
--- a/mm/Makefile
+++ b/mm/Makefile
@@ -51,6 +51,7 @@ 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-$(CONFIG_CGROUP_MEMPRESSURE) += mempressure.o
obj-$(CONFIG_CGROUP_HUGETLB) += hugetlb_cgroup.o
obj-$(CONFIG_MEMORY_FAILURE) += memory-failure.o
obj-$(CONFIG_HWPOISON_INJECT) += hwpoison-inject.o
diff --git a/mm/mempressure.c b/mm/mempressure.c
new file mode 100644
index 0000000..ea312bb
--- /dev/null
+++ b/mm/mempressure.c
@@ -0,0 +1,330 @@
+/*
+ * 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/sched.h>
+#include <linux/mm.h>
+#include <linux/vmstat.h>
+#include <linux/eventfd.h>
+#include <linux/swap.h>
+#include <linux/printk.h>
+
+static void mpc_vmpressure(struct mem_cgroup *memcg, ulong s, ulong r);
+
+/*
+ * Generic VM Pressure routines (no cgroups or any other API details)
+ */
+
+/*
+ * The window size is the number of scanned pages before we try to analyze
+ * the scanned/reclaimed ratio (or difference).
+ *
+ * It is used as a rate-limit tunable for the "low" level notification,
+ * and for averaging medium/oom levels. Using small window sizes can cause
+ * lot of false positives, but too big window size will delay the
+ * notifications.
+ */
+static const uint vmpressure_win = SWAP_CLUSTER_MAX * 16;
+static const uint vmpressure_level_med = 60;
+static const uint vmpressure_level_oom = 99;
+static const uint vmpressure_level_oom_prio = 4;
+
+enum vmpressure_levels {
+ VMPRESSURE_LOW = 0,
+ VMPRESSURE_MEDIUM,
+ VMPRESSURE_OOM,
+ VMPRESSURE_NUM_LEVELS,
+};
+
+static const char *vmpressure_str_levels[] = {
+ [VMPRESSURE_LOW] = "low",
+ [VMPRESSURE_MEDIUM] = "medium",
+ [VMPRESSURE_OOM] = "oom",
+};
+
+static enum vmpressure_levels vmpressure_level(uint pressure)
+{
+ if (pressure >= vmpressure_level_oom)
+ return VMPRESSURE_OOM;
+ else if (pressure >= vmpressure_level_med)
+ return VMPRESSURE_MEDIUM;
+ return VMPRESSURE_LOW;
+}
+
+static ulong vmpressure_calc_level(uint win, uint s, uint r)
+{
+ ulong p;
+
+ if (!s)
+ return 0;
+
+ /*
+ * 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.
+ */
+ p = win - (r * win / s);
+ p = p * 100 / win;
+
+ pr_debug("%s: %3lu (s: %6u r: %6u)\n", __func__, p, s, r);
+
+ return vmpressure_level(p);
+}
+
+void vmpressure(struct mem_cgroup *memcg, ulong scanned, ulong reclaimed)
+{
+ if (!scanned)
+ return;
+ mpc_vmpressure(memcg, scanned, reclaimed);
+}
+
+void vmpressure_prio(struct mem_cgroup *memcg, int prio)
+{
+ if (prio > vmpressure_level_oom_prio)
+ return;
+
+ /* OK, the prio is below the threshold, send the pre-OOM event. */
+ vmpressure(memcg, vmpressure_win, 0);
+}
+
+/*
+ * Memory pressure cgroup code
+ */
+
+struct mpc_event {
+ struct eventfd_ctx *efd;
+ enum vmpressure_levels level;
+ struct list_head node;
+};
+
+struct mpc_state {
+ struct cgroup_subsys_state css;
+
+ uint scanned;
+ uint reclaimed;
+ struct mutex sr_lock;
+
+ struct list_head events;
+ struct mutex events_lock;
+
+ struct work_struct work;
+};
+
+static struct mpc_state *wk2mpc(struct work_struct *wk)
+{
+ return container_of(wk, struct mpc_state, work);
+}
+
+static struct mpc_state *css2mpc(struct cgroup_subsys_state *css)
+{
+ return container_of(css, struct mpc_state, css);
+}
+
+static struct mpc_state *tsk2mpc(struct task_struct *tsk)
+{
+ return css2mpc(task_subsys_state(tsk, mpc_cgroup_subsys_id));
+}
+
+static struct mpc_state *cg2mpc(struct cgroup *cg)
+{
+ return css2mpc(cgroup_subsys_state(cg, mpc_cgroup_subsys_id));
+}
+
+static void mpc_event(struct mpc_state *mpc, ulong s, ulong r)
+{
+ struct mpc_event *ev;
+ int level = vmpressure_calc_level(vmpressure_win, s, r);
+
+ mutex_lock(&mpc->events_lock);
+
+ list_for_each_entry(ev, &mpc->events, node) {
+ if (level >= ev->level)
+ eventfd_signal(ev->efd, 1);
+ }
+
+ mutex_unlock(&mpc->events_lock);
+}
+
+static void mpc_vmpressure_wk_fn(struct work_struct *wk)
+{
+ struct mpc_state *mpc = wk2mpc(wk);
+ ulong s;
+ ulong r;
+
+ mutex_lock(&mpc->sr_lock);
+ s = mpc->scanned;
+ r = mpc->reclaimed;
+ mpc->scanned = 0;
+ mpc->reclaimed = 0;
+ mutex_unlock(&mpc->sr_lock);
+
+ mpc_event(mpc, s, r);
+}
+
+static void __mpc_vmpressure(struct mpc_state *mpc, ulong s, ulong r)
+{
+ mutex_lock(&mpc->sr_lock);
+ mpc->scanned += s;
+ mpc->reclaimed += r;
+ mutex_unlock(&mpc->sr_lock);
+
+ if (s < vmpressure_win || work_pending(&mpc->work))
+ return;
+
+ schedule_work(&mpc->work);
+}
+
+static void mpc_vmpressure(struct mem_cgroup *memcg, ulong s, ulong r)
+{
+ /*
+ * There are two options for implementing cgroup pressure
+ * notifications:
+ *
+ * - Store pressure counter atomically in the task struct. Upon
+ * hitting 'window' wake up a workqueue that will walk every
+ * task and sum per-thread pressure into cgroup pressure (to
+ * which the task belongs). The cons are obvious: bloats task
+ * struct, have to walk all processes and makes pressue less
+ * accurate (the window becomes per-thread);
+ *
+ * - Store pressure counters in per-cgroup state. This is easy and
+ * straightforward, and that's how we do things here. But this
+ * requires us to not put the vmpressure hooks into hotpath,
+ * since we have to grab some locks.
+ */
+
+#ifdef CONFIG_MEMCG
+ if (memcg) {
+ struct cgroup_subsys_state *css = mem_cgroup_css(memcg);
+ struct cgroup *cg = css->cgroup;
+ struct mpc_state *mpc = cg2mpc(cg);
+
+ if (mpc)
+ __mpc_vmpressure(mpc, s, r);
+ return;
+ }
+#endif
+ task_lock(current);
+ __mpc_vmpressure(tsk2mpc(current), s, r);
+ task_unlock(current);
+}
+
+static struct cgroup_subsys_state *mpc_css_alloc(struct cgroup *cg)
+{
+ struct mpc_state *mpc;
+
+ mpc = kzalloc(sizeof(*mpc), GFP_KERNEL);
+ if (!mpc)
+ return ERR_PTR(-ENOMEM);
+
+ mutex_init(&mpc->sr_lock);
+ mutex_init(&mpc->events_lock);
+ INIT_LIST_HEAD(&mpc->events);
+ INIT_WORK(&mpc->work, mpc_vmpressure_wk_fn);
+
+ return &mpc->css;
+}
+
+static void mpc_css_free(struct cgroup *cg)
+{
+ struct mpc_state *mpc = cg2mpc(cg);
+
+ kfree(mpc);
+}
+
+static ssize_t mpc_read_level(struct cgroup *cg, struct cftype *cft,
+ struct file *file, char __user *buf,
+ size_t sz, loff_t *ppos)
+{
+ struct mpc_state *mpc = cg2mpc(cg);
+ uint level;
+ const char *str;
+
+ mutex_lock(&mpc->sr_lock);
+
+ level = vmpressure_calc_level(vmpressure_win,
+ mpc->scanned, mpc->reclaimed);
+
+ mutex_unlock(&mpc->sr_lock);
+
+ str = vmpressure_str_levels[level];
+ return simple_read_from_buffer(buf, sz, ppos, str, strlen(str));
+}
+
+static int mpc_register_level(struct cgroup *cg, struct cftype *cft,
+ struct eventfd_ctx *eventfd, const char *args)
+{
+ struct mpc_state *mpc = cg2mpc(cg);
+ struct mpc_event *ev;
+ int lvl;
+
+ for (lvl = 0; lvl < VMPRESSURE_NUM_LEVELS; lvl++) {
+ if (!strcmp(vmpressure_str_levels[lvl], args))
+ break;
+ }
+
+ if (lvl >= VMPRESSURE_NUM_LEVELS)
+ return -EINVAL;
+
+ ev = kzalloc(sizeof(*ev), GFP_KERNEL);
+ if (!ev)
+ return -ENOMEM;
+
+ ev->efd = eventfd;
+ ev->level = lvl;
+
+ mutex_lock(&mpc->events_lock);
+ list_add(&ev->node, &mpc->events);
+ mutex_unlock(&mpc->events_lock);
+
+ return 0;
+}
+
+static void mpc_unregister_level(struct cgroup *cg, struct cftype *cft,
+ struct eventfd_ctx *eventfd)
+{
+ struct mpc_state *mpc = cg2mpc(cg);
+ struct mpc_event *ev;
+
+ mutex_lock(&mpc->events_lock);
+ list_for_each_entry(ev, &mpc->events, node) {
+ if (ev->efd != eventfd)
+ continue;
+ list_del(&ev->node);
+ kfree(ev);
+ break;
+ }
+ mutex_unlock(&mpc->events_lock);
+}
+
+static struct cftype mpc_files[] = {
+ {
+ .name = "level",
+ .read = mpc_read_level,
+ .register_event = mpc_register_level,
+ .unregister_event = mpc_unregister_level,
+ },
+ {},
+};
+
+struct cgroup_subsys mpc_cgroup_subsys = {
+ .name = "mempressure",
+ .subsys_id = mpc_cgroup_subsys_id,
+ .css_alloc = mpc_css_alloc,
+ .css_free = mpc_css_free,
+ .base_cftypes = mpc_files,
+};
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 16b42af..fed0e04 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1900,6 +1900,9 @@ restart:
shrink_active_list(SWAP_CLUSTER_MAX, lruvec,
sc, LRU_ACTIVE_ANON);

+ vmpressure(sc->target_mem_cgroup,
+ sc->nr_scanned - nr_scanned, nr_reclaimed);
+
/* reclaim/compaction might need reclaim to continue */
if (should_continue_reclaim(lruvec, nr_reclaimed,
sc->nr_scanned - nr_scanned, sc))
@@ -2122,6 +2125,7 @@ static unsigned long do_try_to_free_pages(struct zonelist *zonelist,
count_vm_event(ALLOCSTALL);

do {
+ vmpressure_prio(sc->target_mem_cgroup, sc->priority);
sc->nr_scanned = 0;
aborted_reclaim = shrink_zones(zonelist, sc);

--
1.8.0.2


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