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

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Message-ID: <aXsLKxukv60p3QWF@intel.com>
Date: Thu, 29 Jan 2026 15:24:27 +0800
From: Zhao Liu <zhao1.liu@...el.com>
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>,
	Hao Li <hao.li@...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:
> Date: Fri, 23 Jan 2026 07:52:44 +0100
> From: Vlastimil Babka <vbabka@...e.cz>
> Subject: [PATCH v4 06/22] slab: add sheaves to most caches
> X-Mailer: b4 0.14.3
> 
> 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>
> ---
>  include/linux/slab.h |  6 ------
>  mm/slub.c            | 56 ++++++++++++++++++++++++++++++++++++++++++++++++----
>  2 files changed, 52 insertions(+), 10 deletions(-)

vm_area_cachep's capacity seems to be adjusted to 60 and
maple_node_cache keeps 32 as the args setting.

I still use will-it-scale to evaluate the impact of this patch, and
performance results appear to be on par with previous ones (*) - doesn't
have regression on my cases.

Based on the results of previous capacity adjustments testing, I think
it shows that the capacity of the maple_node_cache appears to have the
significant impact.

There may still be room for optimization in maple_node_cache. As a
general-purpose algorithm at present, I think it has achieved its
intended purpose based on my test results. So,

Tested-by: Zhao Liu <zhao1.liu@...el.com>


(*): The previous ones include 2 cases:
  1) w/o this series, and directly based on the previous commit ("slub:
     keep empty main sheaf as spare in __pcs_replace_empty_main()").
  2) w/o this single patch, and based on the previous patch 5.

Regards,
Zhao