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

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Message-ID: <20260113183604.ykHFYvV2@linutronix.de>
Date: Tue, 13 Jan 2026 19:36:04 +0100
From: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
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>,
	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@...ck.org,
	linux-kernel@...r.kernel.org, linux-rt-devel@...ts.linux.dev,
	bpf@...r.kernel.org, kasan-dev@...glegroups.com
Subject: Re: [PATCH RFC v2 06/20] slab: make percpu sheaves compatible with
 kmalloc_nolock()/kfree_nolock()

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)

> +
> +	ret = ERR_PTR(-EBUSY);
> +
>  	/*
>  	 * Do not call slab_alloc_node(), since trylock mode isn't
>  	 * compatible with slab_pre_alloc_hook/should_failslab and

Sebastian