linux-kernel - Re: [PATCH v2 1/2] mm, slab: Extend slab/shrink to shrink all memcg caches

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Date:   Thu, 18 Jul 2019 17:05:04 +0000
From:   Roman Gushchin <guro@...com>
To:     Christopher Lameter <cl@...ux.com>
CC:     Waiman Long <longman@...hat.com>,
        Pekka Enberg <penberg@...nel.org>,
        "David Rientjes" <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        "Andrew Morton" <akpm@...ux-foundation.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Michal Hocko <mhocko@...nel.org>,
        "Johannes Weiner" <hannes@...xchg.org>,
        Shakeel Butt <shakeelb@...gle.com>,
        "Vladimir Davydov" <vdavydov.dev@...il.com>
Subject: Re: [PATCH v2 1/2] mm, slab: Extend slab/shrink to shrink all memcg
 caches

On Thu, Jul 18, 2019 at 11:38:11AM +0000, Christopher Lameter wrote:
> On Wed, 17 Jul 2019, Waiman Long wrote:
> 
> > Currently, a value of '1" is written to /sys/kernel/slab/<slab>/shrink
> > file to shrink the slab by flushing out all the per-cpu slabs and free
> > slabs in partial lists. This can be useful to squeeze out a bit more memory
> > under extreme condition as well as making the active object counts in
> > /proc/slabinfo more accurate.
> 
> Acked-by: Christoph Lameter <cl@...ux.com>
> 
> >  # grep task_struct /proc/slabinfo
> >  task_struct        53137  53192   4288   61    4 : tunables    0    0
> >  0 : slabdata    872    872      0
> >  # grep "^S[lRU]" /proc/meminfo
> >  Slab:            3936832 kB
> >  SReclaimable:     399104 kB
> >  SUnreclaim:      3537728 kB
> >
> > After shrinking slabs:
> >
> >  # grep "^S[lRU]" /proc/meminfo
> >  Slab:            1356288 kB
> >  SReclaimable:     263296 kB
> >  SUnreclaim:      1092992 kB
> 
> Well another indicator that it may not be a good decision to replicate the
> whole set of slabs for each memcg. Migrate the memcg ownership into the
> objects may allow the use of the same slab cache. In particular together
> with the slab migration patches this may be a viable way to reduce memory
> consumption.
> 

Btw I'm working on an alternative solution. It's way too early to present
anything, but preliminary results are looking promising: slab memory usage
is decreased by 10-40% depending on the workload.

Thanks!