linux-kernel - Re: [RFC 2/2] mm, slub: add shrinker to reclaim cached slabs

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Message-ID: <51de513a-9c4e-35fa-fd04-977480ac50a0@suse.cz>
Date:   Tue, 26 Jan 2021 13:06:35 +0100
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Roman Gushchin <guro@...com>
Cc:     akpm@...ux-foundation.org, bigeasy@...utronix.de, cl@...ux.com,
        hannes@...xchg.org, iamjoonsoo.kim@....com, jannh@...gle.com,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        mhocko@...nel.org, minchan@...nel.org, penberg@...nel.org,
        rientjes@...gle.com, shakeelb@...gle.com, surenb@...gle.com,
        tglx@...utronix.de
Subject: Re: [RFC 2/2] mm, slub: add shrinker to reclaim cached slabs

On 1/22/21 1:48 AM, Roman Gushchin wrote:
> On Thu, Jan 21, 2021 at 06:21:54PM +0100, Vlastimil Babka wrote:
> 
> Hi Vlastimil!
> 
> This makes a lot of sense, however it looks a bit as an overkill to me (on 5.9+).
> Isn't limiting a number of pages (instead of number of objects) sufficient on 5.9+?

It would help, but fundamentally there can still be a lot of memory locked up
with e.g. many CPU's. We should have a way to flush this automatically, like for
other cached things.

> If not, maybe we can limit the shrinking to the pre-OOM condition?
> Do we really need to trip it constantly?

The priority could be reduced, pre-OOM might be too extreme. Why reclaim e.g.
actually used LRU pages instead of unused slab pages?
IMHO a frequently reclaiming system probably doesn't benefit from SLUB's peak
performance at that point anyway...

> Thanks!
>