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

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Message-ID: <20180528091110.GG1517@dhcp22.suse.cz>
Date:   Mon, 28 May 2018 11:11:10 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Shakeel Butt <shakeelb@...gle.com>
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 Sat 26-05-18 15:37:05, Shakeel Butt wrote:
> 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.

What is the limit good for then? Accounting?

-- 
Michal Hocko
SUSE Labs