linux-kernel - Re: [PATCH] memcg: force charge kmem counter too

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Message-ID: <CALvZod67qzq+hQLms4Wut5LNVBjBcEQPpMp9zxF6NE5k+7CLOw@mail.gmail.com>
Date:   Wed, 30 May 2018 11:14:33 -0700
From:   Shakeel Butt <shakeelb@...gle.com>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Vladimir Davydov <vdavydov.dev@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Greg Thelen <gthelen@...gle.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Linux MM <linux-mm@...ck.org>,
        Cgroups <cgroups@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] memcg: force charge kmem counter too

On Tue, May 29, 2018 at 1:31 AM, Michal Hocko <mhocko@...nel.org> wrote:
> On Mon 28-05-18 10:23:07, Shakeel Butt wrote:
>> On Mon, May 28, 2018 at 2:11 AM, Michal Hocko <mhocko@...nel.org> wrote:
>> Though is there a precedence where the broken feature is not fixed
>> because an alternative is available?
>
> Well, I can see how breaking GFP_NOFAIL semantic is problematic, on the
> other hand we keep saying that kmem accounting in v1 is hard usable and
> strongly discourage people from using it. Sure we can add the code which
> handles _this_ particular case but that wouldn't make the whole thing
> more usable I strongly suspect. Maybe I am wrong and you can provide
> some specific examples. Is GFP_NOFAIL that common to matter?
>
> In any case we should balance between the code maintainability here.
> Adding more cruft into the allocator path is not free.
>

We do not use kmem limits internally and this is something I found
through code inspection. If this patch is increasing the cost of code
maintainability I am fine with dropping it but at least there should a
comment saying that kmem limits are broken and no need fix.

Shakeel