memcg: add memory.pressure_level events

With this patch userland applications that want to maintain the
interactivity/memory allocation cost can use the pressure level
notifications.  The levels are defined like this:

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.)

Performance wise, the memory pressure notifications feature itself is
lightweight and does not require much of bookkeeping, in contrast to the
rest of memcg features.  Unfortunately, as of current memcg
implementation, pages accounting is an inseparable part and cannot be
turned off.  The good news is that there are some efforts[1] to improve
the situation; plus, implementing the same, fully API-compatible[2]
interface for CONFIG_MEMCG=n case (e.g.  embedded) is also a viable
option, so it will not require any changes on the userland side.

[1] http://permalink.gmane.org/gmane.linux.kernel.cgroups/6291
[2] http://lkml.org/lkml/2013/2/21/454

[akpm@linux-foundation.org: coding-style fixes]
[akpm@linux-foundation.org: fix CONFIG_CGROPUPS=n warnings]
Signed-off-by: Anton Vorontsov <anton.vorontsov@linaro.org>
Acked-by: Kirill A. Shutemov <kirill@shutemov.name>
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Glauber Costa <glommer@parallels.com>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Luiz Capitulino <lcapitulino@redhat.com>
Cc: Greg Thelen <gthelen@google.com>
Cc: Leonid Moiseichuk <leonid.moiseichuk@nokia.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@gmail.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Cc: John Stultz <john.stultz@linaro.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 29 insertions, 0 deletions

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 7e5bc43c2d1f..360464f40e96 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -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>
@@ -261,6 +262,9 @@ struct mem_cgroup {
          */
         struct res_counter res;
 
+        /* vmpressure notifications */
+        struct vmpressure vmpressure;
+
         union {
                 /*
                  * the counter to account for mem+swap usage.
@@ -359,6 +363,7 @@ 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.
@@ -510,6 +515,24 @@ 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);
@@ -5907,6 +5930,11 @@ 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",
@@ -6188,6 +6216,7 @@ 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;