linux-kernel - Re: [PATCH] mm/slab: fix kmemcg cache creation delayed issue

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Message-ID: <20161013074220.GB2306@js1304-P5Q-DELUXE>
Date:   Thu, 13 Oct 2016 16:42:20 +0900
From:   Joonsoo Kim <iamjoonsoo.kim@....com>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Doug Smythies <dsmythies@...us.net>,
        'Andrew Morton' <akpm@...ux-foundation.org>,
        'Christoph Lameter' <cl@...ux.com>,
        'Pekka Enberg' <penberg@...nel.org>,
        'David Rientjes' <rientjes@...gle.com>,
        'Johannes Weiner' <hannes@...xchg.org>,
        'Vladimir Davydov' <vdavydov.dev@...il.com>,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        stable@...r.kernel.org
Subject: Re: [PATCH] mm/slab: fix kmemcg cache creation delayed issue

On Fri, Oct 07, 2016 at 10:20:55AM +0200, Michal Hocko wrote:
> On Fri 07-10-16 14:14:01, Joonsoo Kim wrote:
> > On Thu, Oct 06, 2016 at 09:02:00AM -0700, Doug Smythies wrote:
> > > It was my (limited) understanding that the subsequent 2 patch set
> > > superseded this patch. Indeed, the 2 patch set seems to solve
> > > both the SLAB and SLUB bug reports.
> > 
> > It would mean that patch 1 solves both the SLAB and SLUB bug reports
> > since patch 2 is only effective for SLUB.
> > 
> > Reason that I send this patch is that although patch 1 fixes the
> > issue that too many kworkers are created, kmem_cache creation/destory
> > is still slowed by synchronize_sched() and it would cause kmemcg
> > usage counting delayed. I'm not sure how bad it is but it's generally
> > better to start accounting as soon as possible. With patch 2 for SLUB
> > and this patch for SLAB, performance of kmem_cache
> > creation/destory would recover.
> 
> OK, so do we really want/need it for stable as well. I am not opposing
> that but the effect doesn't seem to be a clear cut.

I think that it's meaningful to solve problematic commit itself
because it would cause the other problem in the future. And, this patch
is simple enough to apply to the stable tree.

Thanks.