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Date:   Fri, 27 Jan 2017 21:06:56 +0300
From:   Vladimir Davydov <>
To:     Tejun Heo <>
Subject: Re: [PATCH 06/10] slab: implement slab_root_caches list

On Tue, Jan 17, 2017 at 03:54:07PM -0800, Tejun Heo wrote:
> With kmem cgroup support enabled, kmem_caches can be created and
> destroyed frequently and a great number of near empty kmem_caches can
> accumulate if there are a lot of transient cgroups and the system is
> not under memory pressure.  When memory reclaim starts under such
> conditions, it can lead to consecutive deactivation and destruction of
> many kmem_caches, easily hundreds of thousands on moderately large
> systems, exposing scalability issues in the current slab management
> code.  This is one of the patches to address the issue.
> slab_caches currently lists all caches including root and memcg ones.
> This is the only data structure which lists the root caches and
> iterating root caches can only be done by walking the list while
> skipping over memcg caches.  As there can be a huge number of memcg
> caches, this can become very expensive.
> This also can make /proc/slabinfo behave very badly.  seq_file
> processes reads in 4k chunks and seeks to the previous Nth position on
> slab_caches list to resume after each chunk.  With a lot of memcg
> cache churns on the list, reading /proc/slabinfo can become very slow
> and its content often ends up with duplicate and/or missing entries.
> This patch adds a new list slab_root_caches which lists only the root
> caches.  When memcg is not enabled, it becomes just an alias of
> slab_caches.  memcg specific list operations are collected into
> memcg_[un]link_cache().
> Signed-off-by: Tejun Heo <>
> Reported-by: Jay Vana <>
> Cc: Vladimir Davydov <>
> Cc: Christoph Lameter <>
> Cc: Pekka Enberg <>
> Cc: David Rientjes <>
> Cc: Joonsoo Kim <>
> Cc: Andrew Morton <>

Acked-by: Vladimir Davydov <>

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