linux-kernel - Re: [PATCH 4.20 71/92] Revert "mm: slowly shrink slabs with a relatively small number of objects"

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Date:   Mon, 18 Feb 2019 20:14:21 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Roman Gushchin <guro@...com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Rik van Riel <riel@...riel.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>,
        Dave Chinner <dchinner@...hat.com>,
        Wolfgang Walter <linux@...m.de>, Spock <dairinin@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH 4.20 71/92] Revert "mm: slowly shrink slabs with a
 relatively small number of objects"

On Mon 18-02-19 18:57:45, Roman Gushchin wrote:
> On Mon, Feb 18, 2019 at 06:38:25PM +0100, Michal Hocko wrote:
> > On Mon 18-02-19 17:16:34, Greg KH wrote:
> > > On Mon, Feb 18, 2019 at 10:30:44AM -0500, Rik van Riel wrote:
> > > > On Mon, 2019-02-18 at 14:43 +0100, Greg Kroah-Hartman wrote:
> > > > > 4.20-stable review patch.  If anyone has any objections, please let
> > > > > me know.
> > > > > 
> > > > > ------------------
> > > > > 
> > > > > From: Dave Chinner <dchinner@...hat.com>
> > > > > 
> > > > > commit a9a238e83fbb0df31c3b9b67003f8f9d1d1b6c96 upstream.
> > > > > 
> > > > > This reverts commit 172b06c32b9497 ("mm: slowly shrink slabs with a
> > > > > relatively small number of objects").
> > > > 
> > > > This revert will result in the slab caches of dead
> > > > cgroups with a small number of remaining objects never
> > > > getting reclaimed, which can be a memory leak in some
> > > > configurations.
> > > > 
> > > > But hey, that's your tradeoff to make.
> > > 
> > > That's what is in Linus's tree.  Should we somehow diverge from that?
> > 
> > I believe we should start working on a memcg specific solution to
> > minimize regressions for others and start a more complex solution from
> > there.
> > 
> > Can we special case dead memcgs in the slab reclaim and reclaim more
> > aggressively?
> 
> It's probably better to start a new thread to discuss this issue

agreed

> (btw, doesn't LSF/MM looks like the best place to do it? I can send a proposal).

I was about to do that if nobody else did.

dropped the rest of the email because this really deserves a new
discussion.
-- 
Michal Hocko
SUSE Labs