linux-kernel - Re: [PATCH v2 3/3] fs: fsnotify: account fsnotify metadata to kmemcg

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Date:   Thu, 22 Feb 2018 14:49:44 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Shakeel Butt <shakeelb@...gle.com>
Cc:     Jan Kara <jack@...e.cz>, Amir Goldstein <amir73il@...il.com>,
        Christoph Lameter <cl@...ux.com>,
        Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Greg Thelen <gthelen@...gle.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        Mel Gorman <mgorman@...e.de>, Vlastimil Babka <vbabka@...e.cz>,
        linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
        cgroups@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 3/3] fs: fsnotify: account fsnotify metadata to kmemcg

On Tue 20-02-18 19:01:01, Shakeel Butt wrote:
> A lot of memory can be consumed by the events generated for the huge or
> unlimited queues if there is either no or slow listener. This can cause
> system level memory pressure or OOMs. So, it's better to account the
> fsnotify kmem caches to the memcg of the listener.

How much memory are we talking about here?

> There are seven fsnotify kmem caches and among them allocations from
> dnotify_struct_cache, dnotify_mark_cache, fanotify_mark_cache and
> inotify_inode_mark_cachep happens in the context of syscall from the
> listener. So, SLAB_ACCOUNT is enough for these caches.
> 
> The objects from fsnotify_mark_connector_cachep are not accounted as
> they are small compared to the notification mark or events and it is
> unclear whom to account connector to since it is shared by all events
> attached to the inode.
> 
> The allocations from the event caches happen in the context of the event
> producer. For such caches we will need to remote charge the allocations
> to the listener's memcg. Thus we save the memcg reference in the
> fsnotify_group structure of the listener.

Is it typical that the listener lives in a different memcg and if yes
then cannot this cause one memcg to OOM/DoS the one with the listener?

> This patch has also moved the members of fsnotify_group to keep the
> size same, at least for 64 bit build, even with additional member by
> filling the holes.
> 
> Signed-off-by: Shakeel Butt <shakeelb@...gle.com>
[...]
-- 
Michal Hocko
SUSE Labs