linux-kernel - Re: [PATCH v3 14/21] slab: simplify kmalloc

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Message-ID: <2tvnelafuozzzfyvmxvflqmx2sepgy7ottnw4n2trkh33rrk6b@oewlapq3smvg>
Date: Tue, 20 Jan 2026 20:06:38 +0800
From: Hao Li <hao.li@...ux.dev>
To: Vlastimil Babka <vbabka@...e.cz>
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>, 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
Subject: Re: [PATCH v3 14/21] slab: simplify kmalloc_nolock()

On Fri, Jan 16, 2026 at 03:40:34PM +0100, Vlastimil Babka wrote:
> The kmalloc_nolock() implementation has several complications and
> restrictions due to SLUB's cpu slab locking, lockless fastpath and
> PREEMPT_RT differences. With cpu slab usage removed, we can simplify
> things:
> 
> - relax the PREEMPT_RT context checks as they were before commit
>   a4ae75d1b6a2 ("slab: fix kmalloc_nolock() context check for
>   PREEMPT_RT") and also reference the explanation comment in the page
>   allocator
> 
> - the local_lock_cpu_slab() macros became unused, remove them
> 
> - we no longer need to set up lockdep classes on PREEMPT_RT
> 
> - we no longer need to annotate ___slab_alloc as NOKPROBE_SYMBOL
>   since there's no lockless cpu freelist manipulation anymore
> 
> - __slab_alloc_node() can be called from kmalloc_nolock_noprof()
>   unconditionally. It can also no longer return EBUSY. But trylock
>   failures can still happen so retry with the larger bucket if the
>   allocation fails for any reason.
> 
> Note that we still need __CMPXCHG_DOUBLE, because while it was removed
> we don't use cmpxchg16b on cpu freelist anymore, we still use it on
> slab freelist, and the alternative is slab_lock() which can be
> interrupted by a nmi. Clarify the comment to mention it specifically.
> 
> Signed-off-by: Vlastimil Babka <vbabka@...e.cz>
> ---
>  mm/slab.h |   1 -
>  mm/slub.c | 144 +++++++++++++-------------------------------------------------
>  2 files changed, 29 insertions(+), 116 deletions(-)
> 

Looks good to me.
Reviewed-by: Hao Li <hao.li@...ux.dev>

-- 
Thanks,
Hao