linux-kernel - Re: [PATCH v4 06/22] slab: add sheaves to most caches

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Message-ID: <a9c34ec4-936c-4386-9624-662561f87b84@suse.cz>
Date: Tue, 27 Jan 2026 18:01:57 +0100
From: Vlastimil Babka <vbabka@...e.cz>
To: "Liam R. Howlett" <Liam.Howlett@...cle.com>,
 Harry Yoo <harry.yoo@...cle.com>, Petr Tesarik <ptesarik@...e.com>,
 Christoph Lameter <cl@...two.org>, David Rientjes <rientjes@...gle.com>,
 Roman Gushchin <roman.gushchin@...ux.dev>, Hao Li <hao.li@...ux.dev>,
 Andrew Morton <akpm@...ux-foundation.org>,
 Uladzislau Rezki <urezki@...il.com>, Suren Baghdasaryan <surenb@...gle.com>,
 Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
 Alexei Starovoitov <ast@...nel.org>, linux-mm@...ck.org,
 linux-kernel@...r.kernel.org, linux-rt-devel@...ts.linux.dev,
 bpf@...r.kernel.org, kasan-dev@...glegroups.com
Subject: Re: [PATCH v4 06/22] slab: add sheaves to most caches

On 1/27/26 17:34, Liam R. Howlett wrote:
> * Vlastimil Babka <vbabka@...e.cz> [260123 01:53]:
>> In the first step to replace cpu (partial) slabs with sheaves, enable
>> sheaves for almost all caches. Treat args->sheaf_capacity as a minimum,
>> and calculate sheaf capacity with a formula that roughly follows the
>> formula for number of objects in cpu partial slabs in set_cpu_partial().
>> 
>> This should achieve roughly similar contention on the barn spin lock as
>> there's currently for node list_lock without sheaves, to make
>> benchmarking results comparable. It can be further tuned later.
>> 
>> Don't enable sheaves for bootstrap caches as that wouldn't work. In
>> order to recognize them by SLAB_NO_OBJ_EXT, make sure the flag exists
>> even for !CONFIG_SLAB_OBJ_EXT.
>> 
>> This limitation will be lifted for kmalloc caches after the necessary
>> bootstrapping changes.
>> 
>> Also do not enable sheaves for SLAB_NOLEAKTRACE caches to avoid
>> recursion with kmemleak tracking (thanks to Breno Leitao).
>> 
>> Reviewed-by: Suren Baghdasaryan <surenb@...gle.com>
>> Reviewed-by: Harry Yoo <harry.yoo@...cle.com>
>> Signed-off-by: Vlastimil Babka <vbabka@...e.cz>
> 
> Is there a way to force a specific limit to the sheaf capacity if you
> want a lower number than what is calculated in
> calculate_sheaf_capacity()?

No.

> That is, it seems your code always decides
> if the specified sheaf number is smaller right now.

That's right. It shouldn't break anything, AFAICS.

> I'm not sure it's
> practical to want a smaller number though.

Yeah I found no such reason, so until we stumble upon one, we don't need
such support I think?

> Reviewed-by: Liam R. Howlett <Liam.Howlett@...cle.com>

Thanks!