linux-kernel - Re: [PATCH v3 07/21] slab: make percpu sheaves compatible with kmalloc_nolock()/kfree

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Message-ID: <aW2zmf4dXL5C_Iu2@hyeyoo>
Date: Mon, 19 Jan 2026 13:31:21 +0900
From: Harry Yoo <harry.yoo@...cle.com>
To: Vlastimil Babka <vbabka@...e.cz>
Cc: 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>,
        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 07/21] slab: make percpu sheaves compatible with
 kmalloc_nolock()/kfree_nolock()

On Fri, Jan 16, 2026 at 03:40:27PM +0100, Vlastimil Babka wrote:
> Before we enable percpu sheaves for kmalloc caches, we need to make sure
> kmalloc_nolock() and kfree_nolock() will continue working properly and
> not spin when not allowed to.
> 
> Percpu sheaves themselves use local_trylock() so they are already
> compatible. We just need to be careful with the barn->lock spin_lock.
> Pass a new allow_spin parameter where necessary to use
> spin_trylock_irqsave().
> 
> In kmalloc_nolock_noprof() we can now attempt alloc_from_pcs() safely,
> for now it will always fail until we enable sheaves for kmalloc caches
> next. Similarly in kfree_nolock() we can attempt free_to_pcs().
> 
> Signed-off-by: Vlastimil Babka <vbabka@...e.cz>
> ---

Looks good to me,
Reviewed-by: Harry Yoo <harry.yoo@...cle.com>

with a nit below.

>  mm/slub.c | 79 ++++++++++++++++++++++++++++++++++++++++++++-------------------
>  1 file changed, 56 insertions(+), 23 deletions(-)
> 
> diff --git a/mm/slub.c b/mm/slub.c
> index 706cb6398f05..b385247c219f 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -6703,7 +6735,7 @@ void slab_free(struct kmem_cache *s, struct slab *slab, void *object,
>  
>  	if (likely(!IS_ENABLED(CONFIG_NUMA) || slab_nid(slab) == numa_mem_id())
>  	    && likely(!slab_test_pfmemalloc(slab))) {
> -		if (likely(free_to_pcs(s, object)))
> +		if (likely(free_to_pcs(s, object, true)))
>  			return;
>  	}
>  
> @@ -6964,7 +6996,8 @@ void kfree_nolock(const void *object)
>  	 * since kasan quarantine takes locks and not supported from NMI.
>  	 */
>  	kasan_slab_free(s, x, false, false, /* skip quarantine */true);
> -	do_slab_free(s, slab, x, x, 0, _RET_IP_);
> +	if (!free_to_pcs(s, x, false))
> +		do_slab_free(s, slab, x, x, 0, _RET_IP_);
>  }

nit: Maybe it's not that common but should we bypass sheaves if
it's from remote NUMA node just like slab_free()?

>  EXPORT_SYMBOL_GPL(kfree_nolock);
>  
> @@ -7516,7 +7549,7 @@ int kmem_cache_alloc_bulk_noprof(struct kmem_cache *s, gfp_t flags, size_t size,
>  		size--;
>  	}
>  
> -	i = alloc_from_pcs_bulk(s, size, p);
> +	i = alloc_from_pcs_bulk(s, flags, size, p);
>  
>  	if (i < size) { >  		/*
> 

-- 
Cheers,
Harry / Hyeonggon