linux-kernel - Re: [PATCH RFC 05/19] slab: add sheaves to most caches

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Message-ID: <d70962f3-37c4-4410-9cfb-2c0f5c85470e@suse.cz>
Date: Wed, 29 Oct 2025 16:42:40 +0100
From: Vlastimil Babka <vbabka@...e.cz>
To: Harry Yoo <harry.yoo@...cle.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
 Christoph Lameter <cl@...two.org>, David Rientjes <rientjes@...gle.com>,
 Roman Gushchin <roman.gushchin@...ux.dev>,
 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 RFC 05/19] slab: add sheaves to most caches

On 10/27/25 01:24, Harry Yoo wrote:
> On Thu, Oct 23, 2025 at 03:52:27PM +0200, 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().
> 
> Should we scale sheaf capacity not only based on object size but also
> on the number of CPUs, like calculate_order() does?

We can try that as a follow-up, right now it's trying to roughly match the
pre-existing amount of caching so that bots hopefully won't report
regressions just because it became smaller (like we've already seen for
maple nodes).

>> 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 kmalloc caches yet, as that needs further
>> changes to bootstraping.
>> 
>> Signed-off-by: Vlastimil Babka <vbabka@...e.cz>
>> ---
>