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

Harry Yoo
2026-01-19T04:32:03Z

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>

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