Re: [RFC] Making memcg track ownership per address_space or anon_vma

From: Tejun Heo <tj@kernel.org>
To: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Cc: Greg Thelen <gthelen@google.com>,
	Johannes Weiner <hannes@cmpxchg.org>,
	Michal Hocko <mhocko@suse.cz>, Cgroups <cgroups@vger.kernel.org>,
	"linux-mm@kvack.org" <linux-mm@kvack.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Jan Kara <jack@suse.cz>, Dave Chinner <david@fromorbit.com>,
	Jens Axboe <axboe@kernel.dk>,
	Christoph Hellwig <hch@infradead.org>,
	Li Zefan <lizefan@huawei.com>, Hugh Dickins <hughd@google.com>,
	Roman Gushchin <klamm@yandex-team.ru>
Subject: Re: [RFC] Making memcg track ownership per address_space or anon_vma
Date: Wed, 4 Feb 2015 12:15:12 -0500	[thread overview]
Message-ID: <20150204171512.GB18858@htj.dyndns.org> (raw)
In-Reply-To: <54D1F924.5000001@yandex-team.ru>

Hello,

On Wed, Feb 04, 2015 at 01:49:08PM +0300, Konstantin Khlebnikov wrote:
> I think important shared data must be handled and protected explicitly.
> That 'catch-all' shared container could be separated into several

I kinda disagree.  That'd be a major pain in the ass to use and you
wouldn't know when you got something wrong unless it actually goes
wrong and you know enough about the innerworkings to look for that.
Doesn't sound like a sound design to me.

> memory cgroups depending on importance of files: glibc protected
> with soft guarantee, less important stuff is placed into another
> cgroup and cannot push top-priority libraries out of ram.

That sounds extremely painful.

> If shared files are free for use then that 'shared' container must be
> ready to keep them in memory. Otherwise this need to be fixed at the
> container side: we could ignore mlock for shared inodes or amount of
> such vmas might be limited in per-container basis.
> 
> But sharing responsibility for shared file is vague concept: memory
> usage and limit of container must depends only on its own behavior not
> on neighbors at the same machine.
> 
> 
> Generally incidental sharing could be handled as temporary sharing:
> default policy (if inode isn't pinned to memory cgroup) after some
> time should detect that inode is no longer shared and migrate it into
> original cgroup. Of course task could provide hit: O_NO_MOVEMEM or
> even while memory cgroup where it runs could be marked as "scanner"
> which shouldn't disturb memory classification.

Ditto for annotating each file individually.  Let's please try to stay
away from things like that.  That's mostly a cop-out which is unlikely
to actually benefit the majority of users.

> I've missed obvious solution for controlling memory cgroup for files:
> project id. This persistent integer id stored in file system. For now
> it's implemented only for xfs and used for quota which is orthogonal
> to user/group quotas. We could map some of project id to memory cgroup.
> That is more flexible than per-superblock mark, has no conflicts like
> mark on bind-mount.

Again, hell, no.

Thanks.

-- 
tejun