linux-kernel - Re: [PATCH v3 21/21] mm/slub: cleanup and repurpose some stat items

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Message-ID: <5cf8b74e-5ba3-4788-ba1a-4cfe9ef366d3@suse.cz>
Date: Thu, 22 Jan 2026 10:30:05 +0100
From: Vlastimil Babka <vbabka@...e.cz>
To: Suren Baghdasaryan <surenb@...gle.com>
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>,
 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 v3 21/21] mm/slub: cleanup and repurpose some stat items

On 1/22/26 03:35, Suren Baghdasaryan wrote:
> On Fri, Jan 16, 2026 at 6:41 AM Vlastimil Babka <vbabka@...e.cz> wrote:
>>
>> A number of stat items related to cpu slabs became unused, remove them.
>>
>> Two of those were ALLOC_FASTPATH and FREE_FASTPATH. But instead of
>> removing those, use them instead of ALLOC_PCS and FREE_PCS, since
>> sheaves are the new (and only) fastpaths, Remove the recently added
>> _PCS variants instead.
>>
>> Change where FREE_SLOWPATH is counted so that it only counts freeing of
>> objects by slab users that (for whatever reason) do not go to a percpu
>> sheaf, and not all (including internal) callers of __slab_free(). Thus
>> flushing sheaves (counted by SHEAF_FLUSH) no longer also increments
>> FREE_SLOWPATH.
> 
> nit: I think I understand what you mean but "no longer also
> increments" sounds wrong. Maybe repharase as "Thus sheaf flushing
> (already counted by SHEAF_FLUSH) does not affect FREE_SLOWPATH
> anymore."?

OK will do.

>> @@ -5111,8 +5100,6 @@ static void __slab_free(struct kmem_cache *s, struct slab *slab,
>>         unsigned long flags;
>>         bool on_node_partial;
>>
>> -       stat(s, FREE_SLOWPATH);
> 
> After moving the above accounting to the callers I think there are
> several callers which won't account it anymore:
> - free_deferred_objects
> - memcg_alloc_abort_single
> - slab_free_after_rcu_debug
> - ___cache_free
> 
> Am I missing something or is that intentional?

I'm adding them for completeness, but not to memcg_alloc_abort_single() as
that's not result of a user-initiated-free.