Re: [PATCH 2/2] kernfs: do not account ino_ida allocations to memcg

Tejun Heo
2015-05-05T13:45:21Z

On Tue, May 05, 2015 at 12:45:43PM +0300, Vladimir Davydov wrote:
> root->ino_ida is used for kernfs inode number allocations. Since IDA has
> a layered structure, different IDs can reside on the same layer, which
> is currently accounted to some memory cgroup. The problem is that each
> kmem cache of a memory cgroup has its own directory on sysfs (under
> /sys/fs/kernel/<cache-name>/cgroup). If the inode number of such a
> directory or any file in it gets allocated from a layer accounted to the
> cgroup which the cache is created for, the cgroup will get pinned for
> good, because one has to free all kmem allocations accounted to a cgroup
> in order to release it and destroy all its kmem caches. That said we
> must not account layers of ino_ida to any memory cgroup.
>
> Since per net init operations may create new sysfs entries directly
> (e.g. lo device) or indirectly (nf_conntrack creates a new kmem cache
> per each namespace, which, in turn, creates new sysfs entries), an easy
> way to reproduce this issue is by creating network namespace(s) from
> inside a kmem-active memory cgroup.
>
> Signed-off-by: Vladimir Davydov <vdavydov@parallels.com>

Man, that's nasty. For the kernfs part,

Acked-by: Tejun Heo <tj@kernel.org>

Can you please repost this patch w/ Greg KH cc'd?

Thanks.

--
tejun

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