linux-kernel - Re: [PATCH v3 10/21] slab: remove cpu (partial) slabs usage from allocation paths

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Message-ID: <c6ba66a3-0346-40c3-a27e-5528f30fc782@suse.cz>
Date: Wed, 21 Jan 2026 14:56:41 +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 10/21] slab: remove cpu (partial) slabs usage from
 allocation paths

On 1/20/26 19:06, Suren Baghdasaryan wrote:
> On Fri, Jan 16, 2026 at 2:40 PM Vlastimil Babka <vbabka@...e.cz> wrote:
>>
>> We now rely on sheaves as the percpu caching layer and can refill them
>> directly from partial or newly allocated slabs. Start removing the cpu
>> (partial) slabs code, first from allocation paths.
>>
>> This means that any allocation not satisfied from percpu sheaves will
>> end up in ___slab_alloc(), where we remove the usage of cpu (partial)
>> slabs, so it will only perform get_partial() or new_slab(). In the
>> latter case we reuse alloc_from_new_slab() (when we don't use
>> the debug/tiny alloc_single_from_new_slab() variant).
>>
>> In get_partial_node() we used to return a slab for freezing as the cpu
>> slab and to refill the partial slab. Now we only want to return a single
>> object and leave the slab on the list (unless it became full). We can't
>> simply reuse alloc_single_from_partial() as that assumes freeing uses
>> free_to_partial_list(). Instead we need to use __slab_update_freelist()
>> to work properly against a racing __slab_free().
>>
>> The rest of the changes is removing functions that no longer have any
>> callers.
>>
>> Signed-off-by: Vlastimil Babka <vbabka@...e.cz>
> 
> A couple of nits, but otherwise seems fine to me.
> 
> Reviewed-by: Suren Baghdasaryan <surenb@...gle.com>

Thanks!


 > -static struct slab *get_partial_node(struct kmem_cache *s,
>> -                                    struct kmem_cache_node *n,
>> -                                    struct partial_context *pc)
>> +static void *get_partial_node(struct kmem_cache *s,
>> +                             struct kmem_cache_node *n,
>> +                             struct partial_context *pc)
> 
> Naming for get_partial()/get_partial_node()/get_any_partial() made
> sense when they returned a slab. Now that they return object(s) the
> naming is a bit confusing. I think renaming to
> get_from_partial()/get_from_partial_node()/get_from_any_partial()
> would be more appropriate.

OK, will do.

>> -       }
>> +       freelist = get_partial(s, node, &pc);
> 
> I think all this cleanup results in this `freelist` variable being
> used to always store a single object. Maybe rename it into `object`?

Ack.