linux-kernel - Re: [PATCH v5 6/9] slub: Delay freezing of partial slabs

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Message-ID: <4ebc67be-8286-17e9-da33-225ed75509a6@suse.cz>
Date:   Wed, 22 Nov 2023 12:40:25 +0100
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Chengming Zhou <chengming.zhou@...ux.dev>,
        Mark Brown <broonie@...nel.org>
Cc:     cl@...ux.com, penberg@...nel.org, rientjes@...gle.com,
        iamjoonsoo.kim@....com, akpm@...ux-foundation.org,
        roman.gushchin@...ux.dev, 42.hyeyoo@...il.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org,
        Chengming Zhou <zhouchengming@...edance.com>,
        Matthew Wilcox <willy@...radead.org>
Subject: Re: [PATCH v5 6/9] slub: Delay freezing of partial slabs

On 11/22/23 12:35, Chengming Zhou wrote:
> On 2023/11/22 17:37, Vlastimil Babka wrote:
>> On 11/20/23 19:49, Mark Brown wrote:
>>> On Thu, Nov 02, 2023 at 03:23:27AM +0000, chengming.zhou@...ux.dev wrote:
>>>> From: Chengming Zhou <zhouchengming@...edance.com>
>>>>
>>>> Now we will freeze slabs when moving them out of node partial list to
>>>> cpu partial list, this method needs two cmpxchg_double operations:
>>>>
>>>> 1. freeze slab (acquire_slab()) under the node list_lock
>>>> 2. get_freelist() when pick used in ___slab_alloc()
>>>
>>> Recently -next has been failing to boot on a Raspberry Pi 3 with an arm
>>> multi_v7_defconfig and a NFS rootfs, a bisect appears to point to this
>>> patch (in -next as c8d312e039030edab25836a326bcaeb2a3d4db14) as having
>>> introduced the issue.  I've included the full bisect log below.
>>>
>>> When we see problems we see RCU stalls while logging in, for example:
>> 
>> Can you try this, please?
>> 
> 
> Great! I manually disabled __CMPXCHG_DOUBLE to reproduce the problem,
> and this patch can solve the machine hang problem.
> 
> BTW, I also did the performance testcase on the machine with 128 CPUs.
> 
> stress-ng --rawpkt 128 --rawpkt-ops 100000000
> 
> base    patched
> 2.22s   2.35s
> 2.21s   3.14s
> 2.19s   4.75s
> 
> Found this atomic version performance numbers are not stable.

That's weirdly too bad. Is that measured also with __CMPXCHG_DOUBLE
disabled, or just the patch? The PG_workingset flag change should be
uncontended as we are doing it under list_lock, and with __CMPXCHG_DOUBLE
there should be no interfering PG_locked interference.