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Subject[RFC] Add mempressure cgroup
This is an attempt to implement 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

The API uses standard cgroups eventfd notifications:

$ gcc Documentation/cgroups/cgroup_event_listener.c -o \
cgroup_event_listener
$ cd /sys/fs/cgroup/
$ mkdir mempressure
$ mount -t cgroup cgroup ./mempressure -o mempressure
$ cd mempressure
$ cgroup_event_listener ./mempressure.level low
("low", "medium", "oom" are permitted values.)

Upon hitting the threshold, you should see "/sys/fs/cgroup/mempressure
low: crossed" messages.

To test that it actually works on per-cgroup basis, I did a small trick: I
moved all kswapd into a separate cgroup, and hooked the listener onto
another (non-root) cgroup. The listener no longer received global reclaim
pressure, which is expected.

For a task it is possible to be in both cpusets, memcg and mempressure
cgroups, so by rearranging the tasks it should be possible to watch a
specific pressure.

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>
---
include/linux/cgroup_subsys.h | 6 +
include/linux/vmstat.h | 8 ++
init/Kconfig | 5 +
mm/Makefile | 1 +
mm/mempressure.c | 287 ++++++++++++++++++++++++++++++++++++++++++
mm/vmscan.c | 3 +
6 files changed, 310 insertions(+)
create mode 100644 mm/mempressure.c
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 92a86b2..7698341 100644
--- a/include/linux/vmstat.h
+++ b/include/linux/vmstat.h
@@ -10,6 +10,14 @@

extern int sysctl_stat_interval;

+#ifdef CONFIG_CGROUP_MEMPRESSURE
+extern void vmpressure(ulong scanned, ulong reclaimed);
+extern void vmpressure_prio(int prio);
+#else
+static inline void vmpressure(ulong scanned, ulong reclaimed) {}
+static inline void vmpressure_prio(int prio) {}
+#endif
+
#ifdef CONFIG_VM_EVENT_COUNTERS
/*
* Light weight per cpu counter implementation.
diff --git a/init/Kconfig b/init/Kconfig
index 6fdd6e3..7065e44 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -826,6 +826,11 @@ 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
+ TODO
+
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 6b025f8..40cee19 100644
--- a/mm/Makefile
+++ b/mm/Makefile
@@ -50,6 +50,7 @@ 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..5c85bbe
--- /dev/null
+++ b/mm/mempressure.c
@@ -0,0 +1,287 @@
+/*
+ * Linux VM pressure notifications
+ *
+ * Copyright 2012 Linaro Ltd.
+ * Anton Vorontsov <anton.vorontsov@linaro.org>
+ *
+ * Based on ideas from 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/atomic.h>
+#include <linux/eventfd.h>
+#include <linux/swap.h>
+#include <linux/printk.h>
+
+static void mpc_vmpressure(ulong scanned, ulong reclaimed);
+
+/*
+ * Generic VM Pressure routines (no cgroups or any other API details)
+ */
+
+/* These are defaults. Might make them configurable one day. */
+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 const *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(ulong scanned, ulong reclaimed)
+{
+ if (!scanned)
+ return;
+ mpc_vmpressure(scanned, reclaimed);
+}
+
+void vmpressure_prio(int prio)
+{
+ if (prio > vmpressure_level_oom_prio)
+ return;
+
+ /* OK, the prio is below the threshold, send the pre-OOM event. */
+ vmpressure(vmpressure_win, 0);
+}
+
+/*
+ * Memory pressure cgroup code
+ */
+
+struct mpc_state {
+ struct cgroup_subsys_state css;
+ uint scanned;
+ uint reclaimed;
+ struct mutex lock;
+ struct eventfd_ctx *eventfd;
+ enum vmpressure_levels thres;
+};
+
+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_vmpressure(ulong scanned, ulong reclaimed)
+{
+ struct mpc_state *mpc = tsk2mpc(current);
+ int level;
+
+ mpc->scanned += scanned;
+ mpc->reclaimed += reclaimed;
+
+ if (mpc->scanned < vmpressure_win)
+ return;
+
+ level = vmpressure_calc_level(vmpressure_win,
+ mpc->scanned, mpc->reclaimed);
+ if (level >= mpc->thres) {
+ mutex_lock(&mpc->lock);
+ if (mpc->eventfd)
+ eventfd_signal(mpc->eventfd, 1);
+ mutex_unlock(&mpc->lock);
+ }
+}
+
+static void mpc_vmpressure(ulong scanned, ulong reclaimed)
+{
+ /*
+ * 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
+ * straighforward, 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.
+ */
+ task_lock(current);
+ __mpc_vmpressure(scanned, reclaimed);
+ task_unlock(current);
+}
+
+static struct cgroup_subsys_state *mpc_create(struct cgroup *cg)
+{
+ struct mpc_state *mpc;
+
+ mpc = kzalloc(sizeof(*mpc), GFP_KERNEL);
+ if (!mpc)
+ return ERR_PTR(-ENOMEM);
+
+ mutex_init(&mpc->lock);
+
+ return &mpc->css;
+}
+
+static int mpc_pre_destroy(struct cgroup *cg)
+{
+ struct mpc_state *mpc = cg2mpc(cg);
+ int ret = 0;
+
+ mutex_lock(&mpc->lock);
+
+ if (mpc->eventfd)
+ ret = -EBUSY;
+
+ mutex_unlock(&mpc->lock);
+
+ return ret;
+}
+
+static void mpc_destroy(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->lock);
+
+ level = vmpressure_calc_level(vmpressure_win,
+ mpc->scanned, mpc->reclaimed);
+ mpc->scanned = 0;
+ mpc->reclaimed = 0;
+
+ mutex_unlock(&mpc->lock);
+
+ str = vmpressure_str_levels[level];
+ return simple_read_from_buffer(buf, sz, ppos, str, strlen(str));
+}
+
+static int mpc_register_level_event(struct cgroup *cg, struct cftype *cft,
+ struct eventfd_ctx *eventfd,
+ const char *args)
+{
+ struct mpc_state *mpc = cg2mpc(cg);
+ int i;
+ int ret;
+
+ mutex_lock(&mpc->lock);
+
+ /*
+ * It's easy to implement multiple thresholds, but so far we don't
+ * need it.
+ */
+ if (mpc->eventfd) {
+ ret = -EBUSY;
+ goto out_unlock;
+ }
+
+ ret = -EINVAL;
+ for (i = 0; i < VMPRESSURE_NUM_LEVELS; i++) {
+ if (strcmp(vmpressure_str_levels[i], args))
+ continue;
+ mpc->eventfd = eventfd;
+ mpc->thres = i;
+ ret = 0;
+ break;
+ }
+out_unlock:
+ mutex_unlock(&mpc->lock);
+
+ return ret;
+}
+
+static void mpc_unregister_level_event(struct cgroup *cg, struct cftype *cft,
+ struct eventfd_ctx *eventfd)
+{
+ struct mpc_state *mpc = cg2mpc(cg);
+
+ mutex_lock(&mpc->lock);
+ BUG_ON(mpc->eventfd != eventfd);
+ mpc->eventfd = NULL;
+ mutex_unlock(&mpc->lock);
+}
+
+static struct cftype mpc_files[] = {
+ {
+ .name = "level",
+ .read = mpc_read_level,
+ .register_event = mpc_register_level_event,
+ .unregister_event = mpc_unregister_level_event,
+ },
+ {},
+};
+
+struct cgroup_subsys mpc_cgroup_subsys = {
+ .name = "mempressure",
+ .subsys_id = mpc_cgroup_subsys_id,
+ .create = mpc_create,
+ .pre_destroy = mpc_pre_destroy,
+ .destroy = mpc_destroy,
+ .base_cftypes = mpc_files,
+};
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 48550c6..430d8a5 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1877,6 +1877,8 @@ restart:
shrink_active_list(SWAP_CLUSTER_MAX, lruvec,
sc, LRU_ACTIVE_ANON);

+ vmpressure(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))
@@ -2099,6 +2101,7 @@ static unsigned long do_try_to_free_pages(struct zonelist *zonelist,
count_vm_event(ALLOCSTALL);

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

--
1.8.0

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