linux-kernel - Re: [PATCH v4 00/22] slab: replace cpu (partial) slabs with sheaves

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Message-ID: <699982e5-6660-4e48-be57-3ee7326a20d5@suse.cz>
Date: Fri, 6 Feb 2026 17:44:45 +0100
From: Vlastimil Babka <vbabka@...e.cz>
To: "Christoph Lameter (Ampere)" <cl@...two.org>
Cc: Hao Li <hao.li@...ux.dev>, Harry Yoo <harry.yoo@...cle.com>,
 Petr Tesarik <ptesarik@...e.com>, 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,
 kernel test robot <oliver.sang@...el.com>, stable@...r.kernel.org,
 "Paul E. McKenney" <paulmck@...nel.org>
Subject: Re: [PATCH v4 00/22] slab: replace cpu (partial) slabs with sheaves

On 2/4/26 19:24, Christoph Lameter (Ampere) wrote:
> On Wed, 4 Feb 2026, Vlastimil Babka wrote:
> 
>> > So I think the performance of the percpu partial list and the sheaves mechanism
>> > is roughly the same, which is consistent with our expectations.
>>
>> Thanks!
> 
> There are other considerations that usually do not show up well in
> benchmark tests.
> 
> The sheaves cannot do the spatial optimizations that cpu partial lists
> provide. Fragmentation in slab caches (and therefore the nubmer of
> partial slab pages) will increase since
> 
> 1. The objects are not immediately returned to their slab pages but end up
> in some queuing structure.
> 
> 2. Available objects from a single slab page are not allocated in sequence
> to empty partial pages and remove the page from the partial lists.
> 
> Objects are put into some queue on free and are processed on a FIFO basis.
> Objects allocated may come from lots of different slab pages potentially
> increasing TLB pressure.

IIUC this is what you said before [1] and the cover letter has a link and a
summary of it.

[1] https://lore.kernel.org/all/f7c33974-e520-387e-9e2f-1e523bfe1545@gentwo.org/