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

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Message-ID: <7tds765fsicczreeqckiuwpny2tolotfrnbz6jhpjrch6x5pg3@5irfwnohvsli>
Date: Mon, 26 Jan 2026 14:36:02 +0800
From: Hao Li <hao.li@...ux.dev>
To: Vlastimil Babka <vbabka@...e.cz>
Cc: 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>, Andrew Morton <akpm@...ux-foundation.org>, 
	Uladzislau Rezki <urezki@...il.com>, "Liam R. Howlett" <Liam.Howlett@...cle.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 Fri, Jan 23, 2026 at 07:52:44AM +0100, Vlastimil Babka wrote:
> 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>

Also, looks good to me.

As a side node, while looking into the test results reported by Zhao Liu [1], I
ran a quick test of the current patchset with the will-it-scale mmap2 workload.
In my runs, tuning capacity up or down did indeed have a noticeable impact on
performance. Hopefully we can make this tuning even smarter in follow-up work.

[1] https://lore.kernel.org/linux-mm/aWi9nAbIkTfYFoMM@intel.com/

Reviewed-by: Hao Li <hao.li@...ux.dev>

-- 
Thanks,
Hao