Re: [PATCH v13 6/7] mm, oom, docs: describe the cgroup-aware OOM killer

[Michal Hocko]

On Fri 01-12-17 17:01:49, Roman Gushchin wrote:
[...]
> diff --git a/Documentation/cgroup-v2.txt b/Documentation/cgroup-v2.txt
> index c80a147f94b7..ff8e92db636d 100644
> --- a/Documentation/cgroup-v2.txt
> +++ b/Documentation/cgroup-v2.txt
> @@ -1049,6 +1049,9 @@ PAGE_SIZE multiple when read back.
>   and will never kill the unkillable task, even if memory.oom_group
>   is set.
>  
> + If cgroup-aware OOM killer is not enabled, ENOTSUPP error
> + is returned on attempt to access the file.
> +
>memory.events
>   A read-only flat-keyed file which exists on non-root cgroups.
>   The following entries are defined.  Unless specified
> @@ -1258,6 +1261,12 @@ OOM Killer
>  Cgroup v2 memory controller implements a cgroup-aware OOM killer.
>  It means that it treats cgroups as first class OOM entities.
>  
> +Cgroup-aware OOM logic is turned off by default and requires
> +passing the "groupoom" option on mounting cgroupfs. It can also
> +by remounting cgroupfs with the following command::
> +
> +  # mount -o remount,groupoom $MOUNT_POINT
> +
>  Under OOM conditions the memory controller tries to make the best
>  choice of a victim, looking for a memory cgroup with the largest
>  memory footprint, considering leaf cgroups and cgroups with the

Looks good to me

Thanks!
-- 
Michal Hocko
SUSE Labs
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Re: [PATCH v13 6/7] mm, oom, docs: describe the cgroup-aware OOM killer

[Roman Gushchin]

On Fri, Dec 01, 2017 at 09:41:54AM +0100, Michal Hocko wrote:
> On Thu 30-11-17 15:28:23, Roman Gushchin wrote:
> > @@ -1229,6 +1252,41 @@ to be accessed repeatedly by other cgroups, it may 
> > make sense to use
> >  POSIX_FADV_DONTNEED to relinquish the ownership of memory areas
> >  belonging to the affected files to ensure correct memory ownership.
> >  
> > +OOM Killer
> > +~~
> > +
> > +Cgroup v2 memory controller implements a cgroup-aware OOM killer.
> > +It means that it treats cgroups as first class OOM entities.
> 
> This should mention groupoom mount option to enable this functionality.
> 
> Other than that looks ok to me
> Acked-by: Michal Hocko 
> -- 
> Michal Hocko
> SUSE Labs


>From 1d9c87128897ee7f27f9651d75b80f73985373e8 Mon Sep 17 00:00:00 2001
From: Roman Gushchin 
Date: Fri, 1 Dec 2017 15:34:59 +
Subject: [PATCH] mm, oom, docs: document groupoom mount option

Add a note that cgroup-aware OOM logic is disabled by default
and describe how to enable it.

Signed-off-by: Roman Gushchin 
Cc: Andrew Morton 
Cc: Johannes Weiner 
Cc: Michal Hocko 
Cc: Vladimir Davydov 
Cc: Tejun Heo 
Cc: kernel-t...@fb.com
Cc: linux...@kvack.org
Cc: linux-ker...@vger.kernel.org
---
 Documentation/cgroup-v2.txt | 9 +
 1 file changed, 9 insertions(+)

diff --git a/Documentation/cgroup-v2.txt b/Documentation/cgroup-v2.txt
index c80a147f94b7..ff8e92db636d 100644
--- a/Documentation/cgroup-v2.txt
+++ b/Documentation/cgroup-v2.txt
@@ -1049,6 +1049,9 @@ PAGE_SIZE multiple when read back.
and will never kill the unkillable task, even if memory.oom_group
is set.
 
+   If cgroup-aware OOM killer is not enabled, ENOTSUPP error
+   is returned on attempt to access the file.
+
   memory.events
A read-only flat-keyed file which exists on non-root cgroups.
The following entries are defined.  Unless specified
@@ -1258,6 +1261,12 @@ OOM Killer
 Cgroup v2 memory controller implements a cgroup-aware OOM killer.
 It means that it treats cgroups as first class OOM entities.
 
+Cgroup-aware OOM logic is turned off by default and requires
+passing the "groupoom" option on mounting cgroupfs. It can also
+by remounting cgroupfs with the following command::
+
+  # mount -o remount,groupoom $MOUNT_POINT
+
 Under OOM conditions the memory controller tries to make the best
 choice of a victim, looking for a memory cgroup with the largest
 memory footprint, considering leaf cgroups and cgroups with the
-- 
2.14.3

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Re: [PATCH v13 6/7] mm, oom, docs: describe the cgroup-aware OOM killer

[Michal Hocko]

On Thu 30-11-17 15:28:23, Roman Gushchin wrote:
> @@ -1229,6 +1252,41 @@ to be accessed repeatedly by other cgroups, it may 
> make sense to use
>  POSIX_FADV_DONTNEED to relinquish the ownership of memory areas
>  belonging to the affected files to ensure correct memory ownership.
>  
> +OOM Killer
> +~~
> +
> +Cgroup v2 memory controller implements a cgroup-aware OOM killer.
> +It means that it treats cgroups as first class OOM entities.

This should mention groupoom mount option to enable this functionality.

Other than that looks ok to me
Acked-by: Michal Hocko 
-- 
Michal Hocko
SUSE Labs
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[PATCH v13 6/7] mm, oom, docs: describe the cgroup-aware OOM killer

[Roman Gushchin]

Document the cgroup-aware OOM killer.

Signed-off-by: Roman Gushchin 
Cc: Johannes Weiner 
Cc: Michal Hocko 
Cc: Vladimir Davydov 
Cc: Tetsuo Handa 
Cc: Andrew Morton 
Cc: David Rientjes 
Cc: Tejun Heo 
Cc: kernel-t...@fb.com
Cc: cgro...@vger.kernel.org
Cc: linux-doc@vger.kernel.org
Cc: linux-ker...@vger.kernel.org
Cc: linux...@kvack.org
---
 Documentation/cgroup-v2.txt | 58 +
 1 file changed, 58 insertions(+)

diff --git a/Documentation/cgroup-v2.txt b/Documentation/cgroup-v2.txt
index 779211fbb69f..c80a147f94b7 100644
--- a/Documentation/cgroup-v2.txt
+++ b/Documentation/cgroup-v2.txt
@@ -48,6 +48,7 @@ v1 is available under Documentation/cgroup-v1/.
5-2-1. Memory Interface Files
5-2-2. Usage Guidelines
5-2-3. Memory Ownership
+   5-2-4. OOM Killer
  5-3. IO
5-3-1. IO Interface Files
5-3-2. Writeback
@@ -1026,6 +1027,28 @@ PAGE_SIZE multiple when read back.
high limit is used and monitored properly, this limit's
utility is limited to providing the final safety net.
 
+  memory.oom_group
+
+   A read-write single value file which exists on non-root
+   cgroups.  The default is "0".
+
+   If set, OOM killer will consider the memory cgroup as an
+   indivisible memory consumers and compare it with other memory
+   consumers by it's memory footprint.
+   If such memory cgroup is selected as an OOM victim, all
+   processes belonging to it or it's descendants will be killed.
+
+   This applies to system-wide OOM conditions and reaching
+   the hard memory limit of the cgroup and their ancestor.
+   If OOM condition happens in a descendant cgroup with it's own
+   memory limit, the memory cgroup can't be considered
+   as an OOM victim, and OOM killer will not kill all belonging
+   tasks.
+
+   Also, OOM killer respects the /proc/pid/oom_score_adj value -1000,
+   and will never kill the unkillable task, even if memory.oom_group
+   is set.
+
   memory.events
A read-only flat-keyed file which exists on non-root cgroups.
The following entries are defined.  Unless specified
@@ -1229,6 +1252,41 @@ to be accessed repeatedly by other cgroups, it may make 
sense to use
 POSIX_FADV_DONTNEED to relinquish the ownership of memory areas
 belonging to the affected files to ensure correct memory ownership.
 
+OOM Killer
+~~
+
+Cgroup v2 memory controller implements a cgroup-aware OOM killer.
+It means that it treats cgroups as first class OOM entities.
+
+Under OOM conditions the memory controller tries to make the best
+choice of a victim, looking for a memory cgroup with the largest
+memory footprint, considering leaf cgroups and cgroups with the
+memory.oom_group option set, which are considered to be an indivisible
+memory consumers.
+
+By default, OOM killer will kill the biggest task in the selected
+memory cgroup. A user can change this behavior by enabling
+the per-cgroup memory.oom_group option. If set, it causes
+the OOM killer to kill all processes attached to the cgroup,
+except processes with oom_score_adj set to -1000.
+
+This affects both system- and cgroup-wide OOMs. For a cgroup-wide OOM
+the memory controller considers only cgroups belonging to the sub-tree
+of the OOM'ing cgroup.
+
+The root cgroup is treated as a leaf memory cgroup, so it's compared
+with other leaf memory cgroups and cgroups with oom_group option set.
+
+If there are no cgroups with the enabled memory controller,
+the OOM killer is using the "traditional" process-based approach.
+
+Please, note that memory charges are not migrating if tasks
+are moved between different memory cgroups. Moving tasks with
+significant memory footprint may affect OOM victim selection logic.
+If it's a case, please, consider creating a common ancestor for
+the source and destination memory cgroups and enabling oom_group
+on ancestor layer.
+
 
 IO
 --
-- 
2.14.3

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