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From: Roman Gushchin <>
To: Greg Thelen <>
Cc: Johannes Weiner <>,
	Andrew Morton <>,
	Michal Hocko <>,
	Vladimir Davydov <>,
	Tejun Heo <>, Cgroups <>,
	<>, Linux MM <>,
	LKML <>
Subject: Re: [RFC PATCH 0/2] memory.low,min reclaim
Date: Mon, 23 Apr 2018 11:38:10 +0100	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

Hi, Greg!

On Sun, Apr 22, 2018 at 01:26:10PM -0700, Greg Thelen wrote:
> Roman's previously posted memory.low,min patches add per memcg effective
> low limit to detect overcommitment of parental limits.  But if we flip
> low,min reclaim to bail if usage<{low,min} at any level, then we don't need
> an effective low limit, which makes the code simpler.  When parent limits
> are overcommited memory.min will oom kill, which is more drastic but makes
> the memory.low a simpler concept.  If memcg a/b wants oom kill before
> reclaim, then give it to them.  It seems a bit strange for a/b/memory.low's
> behaviour to depend on a/c/memory.low (i.e. a/b.low is strong unless
> a/b.low+a/c.low exceed a.low).

It's actually not strange: a/b and a/c are sharing a common resource:

Exactly as a/b/memory.max and a/c/memory.max are sharing a/memory.max.
If there are sibling cgroups which are consuming memory, a cgroup can't
exceed parent's memory.max, even if its memory.max is grater.

> I think there might be a simpler way (ableit it doesn't yet include
> Documentation):
> - memcg: fix memory.low
> - memcg: add memory.min
>  3 files changed, 75 insertions(+), 6 deletions(-)
> The idea of this alternate approach is for memory.low,min to avoid reclaim
> if any portion of under-consideration memcg ancestry is under respective
> limit.

This approach has a significant downside: it breaks hierarchical constraints
for memory.low/min. There are two important outcomes:

1) Any leaf's memory.low/min value is respected, even if parent's value
   is lower or even 0. It's not possible anymore to limit the amount of
   protected memory for a sub-tree.
   This is especially bad in case of delegation.

2) If a cgroup has an ancestor with the usage under its memory.low/min,
   it becomes protection, even if its memory.low/min is 0. So it becomes
   impossible to have unprotected cgroups in protected sub-tree.


  parent reply	other threads:[~2018-04-23 10:38 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-03-20 22:33 [RFC] mm: memory.low heirarchical behavior Roman Gushchin
2018-03-21 18:23 ` Johannes Weiner
2018-03-21 19:08   ` Roman Gushchin
2018-04-04 17:07     ` Johannes Weiner
2018-04-05 13:54       ` Roman Gushchin
2018-04-05 15:00         ` Johannes Weiner
2018-03-23 16:37   ` [PATCH v2] mm: memory.low hierarchical behavior Roman Gushchin
2018-04-22 20:26 ` [RFC PATCH 0/2] memory.low,min reclaim Greg Thelen
2018-04-22 20:26   ` [RFC PATCH 1/2] memcg: fix memory.low Greg Thelen
2018-04-22 20:26   ` [RFC PATCH 2/2] memcg: add memory.min Greg Thelen
2018-04-23 10:38   ` Roman Gushchin [this message]
2018-04-24  0:56     ` [RFC PATCH 0/2] memory.low,min reclaim Greg Thelen
2018-04-24 10:09       ` Roman Gushchin

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