Re: [PATCH 3/5] slab: handle pfmemalloc slabs properly with sheaves

[Harry Yoo]

On Wed, Nov 05, 2025 at 10:05:31AM +0100, Vlastimil Babka wrote:
> When a pfmemalloc allocation actually dips into reserves, the slab is
> marked accordingly and non-pfmemalloc allocations should not be allowed
> to allocate from it. The sheaves percpu caching currently doesn't follow
> this rule, so implement it before we expand sheaves usage to all caches.
> 
> Make sure objects from pfmemalloc slabs don't end up in percpu sheaves.
> When freeing, skip sheaves when freeing an object from pfmemalloc slab.
> When refilling sheaves, use __GFP_NOMEMALLOC to override any pfmemalloc
> context - the allocation will fallback to regular slab allocations when
> sheaves are depleted and can't be refilled because of the override.
> 
> For kfree_rcu(), detect pfmemalloc slabs after processing the rcu_sheaf
> after the grace period in __rcu_free_sheaf_prepare() and simply flush
> it if any object is from pfmemalloc slabs.
>
> For prefilled sheaves, try to refill them first with __GFP_NOMEMALLOC
> and if it fails, retry without __GFP_NOMEMALLOC but then mark the sheaf
> pfmemalloc, which makes it flushed back to slabs when returned.
> 
> Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx>
> ---

Reviewed-by: Harry Yoo <harry.yoo@xxxxxxxxxx>

-- 
Cheers,
Harry / Hyeonggon