linux-kernel - Re: [PATCH RFC v2 06/20] slab: make percpu sheaves compatible with kmalloc_nolock()/kfree

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Message-ID: <CAADnVQK0Y2ha--EndLUfk_7n8na9CfnTpvqPMYbH07+MTJ9UpA@mail.gmail.com>
Date: Tue, 13 Jan 2026 15:26:53 -0800
From: Alexei Starovoitov <alexei.starovoitov@...il.com>
To: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
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>, Hao Li <hao.li@...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>, 
	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>
Subject: Re: [PATCH RFC v2 06/20] slab: make percpu sheaves compatible with kmalloc_nolock()/kfree_nolock()

On Tue, Jan 13, 2026 at 10:36 AM Sebastian Andrzej Siewior
<bigeasy@...utronix.de> wrote:
>
> On 2026-01-12 16:17:00 [+0100], Vlastimil Babka wrote:
> > --- a/mm/slub.c
> > +++ b/mm/slub.c
> > @@ -5727,6 +5742,12 @@ void *kmalloc_nolock_noprof(size_t size, gfp_t gfp_flags, int node)
> >                */
> >               return NULL;
> >
> > +     ret = alloc_from_pcs(s, alloc_gfp, node);
> > +     if (ret)
> > +             goto success;
>
> I'm sorry if I am slow but this actually should actually allow
> kmalloc_nolock() allocations on PREEMPT_RT from atomic context. I am
> mentioning this because of the patch which removes the nmi+hardirq
> condtion (https://lore.kernel.org/all/20260113150639.48407-1-swarajgaikwad1925@gmail.com)

Right. With sheaves kmalloc_nolock() on RT will be more reliable.