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

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Message-ID: <CALvZod5yTxcuB_Aao-a0ChNEnwyBJk9UPvEQ80s9tZFBQ0cxpw@mail.gmail.com>
Date:   Sat, 26 May 2018 15:37:05 -0700
From:   Shakeel Butt <shakeelb@...gle.com>
To:     Vladimir Davydov <vdavydov.dev@...il.com>
Cc:     Michal Hocko <mhocko@...nel.org>,
        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 Sat, May 26, 2018 at 11:51 AM, Vladimir Davydov
<vdavydov.dev@...il.com> wrote:
> On Fri, May 25, 2018 at 11:55:01AM -0700, Shakeel Butt wrote:
>> Based on several conditions the kernel can decide to force charge an
>> allocation for a memcg i.e. overcharge memcg->memory and memcg->memsw
>> counters. Do the same for memcg->kmem counter too. In cgroup-v1, this
>> bug can cause a __GFP_NOFAIL kmem allocation fail if an explicit limit
>> on kmem counter is set and reached.
>
> memory.kmem.limit is broken and unlikely to ever be fixed as this knob
> was deprecated in cgroup-v2. The fact that hitting the limit doesn't
> trigger reclaim can result in unexpected behavior from user's pov, like
> getting ENOMEM while listing a directory. Bypassing the limit for NOFAIL
> allocations isn't going to fix those problem.

I understand that fixing NOFAIL will not fix all other issues but it
still is better than current situation. IMHO we should keep fixing
kmem bit by bit.

One crazy idea is to just break it completely by force charging all the time.