Re: [PATCH v3 07/21] slab: make percpu sheaves compatible with kmalloc_nolock()/kfree_nolock()

Vlastimil Babka
2026-01-19T10:09:39Z

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@suse.cz>
>> ---
>
> Looks good to me,
> Reviewed-by: Harry Yoo <harry.yoo@oracle.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) { > /*
>>
>