linux-kernel - Re: [PATCH v3 00/35] SLUB: reduce irq disabled scope and make it RT compatible

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Message-ID: <20210804120522.GD6464@techsingularity.net>
Date:   Wed, 4 Aug 2021 13:05:22 +0100
From:   Mel Gorman <mgorman@...hsingularity.net>
To:     Vlastimil Babka <vbabka@...e.cz>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Christoph Lameter <cl@...ux.com>,
        David Rientjes <rientjes@...gle.com>,
        Pekka Enberg <penberg@...nel.org>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Mike Galbraith <efault@....de>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        Jann Horn <jannh@...gle.com>
Subject: Re: [PATCH v3 00/35] SLUB: reduce irq disabled scope and make it RT
 compatible

On Thu, Jul 29, 2021 at 03:20:57PM +0200, Vlastimil Babka wrote:
> Changes since v2 [5]:
> * Rebase to 5.14-rc3
> * A number of fixes to the RT parts, big thanks to Mike Galbraith for testing
>   and debugging!
>   * The largest fix is to protect kmem_cache_cpu->partial by local_lock instead
>     of cmpxchg tricks, which are insufficient on RT. To avoid divergence
>     between RT and !RT, just do it everywhere. Affected mainly patch 25 and a
>     new patch 33. This also addresses a theoretical race raised earlier by Jann
>     Horn.
> * Smaller fixes reported by Sebastian Andrzej Siewior and Cyrill Gorcunov
> 
> Changes since RFC v1 [1]:
> * Addressed feedback from Christoph and Mel, added their acks.
> * Finished RT conversion, adopting 2 patches from the RT tree.
> * The local_lock conversion has to sacrifice lockless fathpaths on PREEMPT_RT
> * Added some more cleanup patches to the front.
> 
> This series was initially inspired by Mel's pcplist local_lock rewrite, and
> also interest to better understand SLUB's locking and the new primitives and RT
> variants and implications. It should make SLUB more preemption-friendly,
> especially for RT, hopefully without noticeable regressions, as the fast paths
> are not affected.
> 
> Series is based on 5.14-rc3 and also available as a git branch:
> https://git.kernel.org/pub/scm/linux/kernel/git/vbabka/linux.git/log/?h=slub-local-lock-v3r1
> 

FWIW, I ran a corrected version of this series through a few tests. Some
small gains, no major regressions in terms of performance on a !PREEMPT_RT
configuration across 6 different machines.

-- 
Mel Gorman
SUSE Labs