linux-kernel - Re: [PATCH v2 0/3] Directed kmem charging

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Date:   Wed, 21 Feb 2018 09:18:35 -0800
From:   Shakeel Butt <shakeelb@...gle.com>
To:     Christopher Lameter <cl@...ux.com>
Cc:     Jan Kara <jack@...e.cz>, Amir Goldstein <amir73il@...il.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>,
        Michal Hocko <mhocko@...nel.org>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        Mel Gorman <mgorman@...e.de>, Vlastimil Babka <vbabka@...e.cz>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Linux MM <linux-mm@...ck.org>,
        Cgroups <cgroups@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 0/3] Directed kmem charging

On Wed, Feb 21, 2018 at 8:09 AM, Christopher Lameter <cl@...ux.com> wrote:
> Another way to solve this is to switch the user context right?
>
> Isnt it possible to avoid these patches if do the allocation in another
> task context instead?
>

Sorry, can you please explain what you mean by 'switch the user
context'. Is there any example in kernel which does something similar?

Another way is by adding a field 'remote_memcg_to_charge' in
task_struct and set it before the allocation and in memcontrol.c,
first check if current->remote_memcg_to_charge is set otherwise use
the memcg of current. Also if we provide a wrapper to do that for the
user, there will be a lot less plumbing.

Please let me know if you prefer this approach.

> Are there really any other use cases beyond fsnotify?
>

Another use case I have in mind and plan to upstream is to bind a
filesystem mount with a memcg. So, all the file pages (or anon pages
for shmem) and kmem (like inodes and dentry) will be charged to that
memcg.

>
> The charging of the memory works on a per page level but the allocation
> occur from the same page for multiple tasks that may be running on a
> system. So how relevant is this for other small objects?
>
> Seems that if you do a large amount of allocations for the same purpose
> your chance of accounting it to the right memcg increases. But this is a
> game of chance.
>
>
>