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Date:   Thu, 22 Feb 2018 14:49:44 +0100
From:   Michal Hocko <mhocko@kernel.org>
To:     Shakeel Butt <shakeelb@google.com>
Cc:     Jan Kara <jack@suse.cz>, Amir Goldstein <amir73il@gmail.com>,
        Christoph Lameter <cl@linux.com>,
        Pekka Enberg <penberg@kernel.org>,
        David Rientjes <rientjes@google.com>,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Greg Thelen <gthelen@google.com>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Vladimir Davydov <vdavydov.dev@gmail.com>,
        Mel Gorman <mgorman@suse.de>, Vlastimil Babka <vbabka@suse.cz>,
        linux-fsdevel@vger.kernel.org, linux-mm@kvack.org,
        cgroups@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 3/3] fs: fsnotify: account fsnotify metadata to kmemcg
Message-ID: <20180222134944.GK30681@dhcp22.suse.cz>
References: <20180221030101.221206-1-shakeelb@google.com>
 <20180221030101.221206-4-shakeelb@google.com>
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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@google.com>
[...]
-- 
Michal Hocko
SUSE Labs