linux-kernel - Re: [PATCH RFC 00/19] slab: replace cpu (partial) slabs with sheaves

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Message-ID: <CAADnVQKYDgwgAQ+geFrY=xDxNoe2YuEYVQU+d3V3nMhkMBg1zw@mail.gmail.com>
Date: Fri, 24 Oct 2025 16:57:18 -0700
From: Alexei Starovoitov <alexei.starovoitov@...il.com>
To: Vlastimil Babka <vbabka@...e.cz>
Cc: Andrew Morton <akpm@...ux-foundation.org>, Christoph Lameter <cl@...two.org>, 
	David Rientjes <rientjes@...gle.com>, Roman Gushchin <roman.gushchin@...ux.dev>, 
	Harry Yoo <harry.yoo@...cle.com>, 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 <linux-mm@...ck.org>, 
	LKML <linux-kernel@...r.kernel.org>, linux-rt-devel@...ts.linux.dev, 
	bpf <bpf@...r.kernel.org>, kasan-dev <kasan-dev@...glegroups.com>, 
	Alexander Potapenko <glider@...gle.com>, Marco Elver <elver@...gle.com>, Dmitry Vyukov <dvyukov@...gle.com>
Subject: Re: [PATCH RFC 00/19] slab: replace cpu (partial) slabs with sheaves

On Thu, Oct 23, 2025 at 6:53 AM Vlastimil Babka <vbabka@...e.cz> wrote:
>
> Percpu sheaves caching was introduced as opt-in but the goal was to
> eventually move all caches to them. This is the next step, enabling
> sheaves for all caches (except the two bootstrap ones) and then removing
> the per cpu (partial) slabs and lots of associated code.
>
> Besides (hopefully) improved performance, this removes the rather
> complicated code related to the lockless fastpaths (using
> this_cpu_try_cmpxchg128/64) and its complications with PREEMPT_RT or
> kmalloc_nolock().
>
> The lockless slab freelist+counters update operation using
> try_cmpxchg128/64 remains and is crucial for freeing remote NUMA objects
> without repeating the "alien" array flushing of SLUB, and to allow
> flushing objects from sheaves to slabs mostly without the node
> list_lock.
>
> This is the first RFC to get feedback. Biggest TODOs are:
>
> - cleanup of stat counters to fit the new scheme
> - integration of rcu sheaves handling with kfree_rcu batching

The whole thing looks good, and imo these two are lower priority.

> - performance evaluation

The performance results will be the key.
What kind of benchmarks do you have in mind?