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

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Message-ID: <CAJuCfpHGSxK99sSDmnh+xqJOaqLX6vVoH4oyPUS7J6J74RU=9A@mail.gmail.com>
Date: Wed, 21 Jan 2026 17:39:00 +0000
From: Suren Baghdasaryan <surenb@...gle.com>
To: Hao Li <hao.li@...ux.dev>
Cc: Vlastimil Babka <vbabka@...e.cz>, 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>, 
	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 Tue, Jan 20, 2026 at 12:07 PM Hao Li <hao.li@...ux.dev> wrote:
>
> 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>

Reviewed-by: Suren Baghdasaryan <surenb@...gle.com>

>
> --
> Thanks,
> Hao