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

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Message-ID: <e4831aab-40e6-48ec-a4b9-1967bd0d6a4c@suse.cz>
Date: Mon, 19 Jan 2026 11:09:37 +0100
From: Vlastimil Babka <vbabka@...e.cz>
To: Harry Yoo <harry.yoo@...cle.com>
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 1/19/26 05:31, Harry Yoo wrote:
> 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>

Thanks.

> 
> 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()?

Right, will do.

>>  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) { >  		/*
>> 
>