Re: [PATCH 2/3] slab: create barns for online memoryless nodes

Harry Yoo
2026-03-16T03:26:27Z

On Wed, Mar 11, 2026 at 09:25:56AM +0100, Vlastimil Babka (SUSE) wrote:
> Ming Lei has reported [1] a performance regression due to replacing cpu
> (partial) slabs with sheaves. With slub stats enabled, a large amount of
> slowpath allocations were observed. The affected system has 8 online
> NUMA nodes but only 2 have memory.
>
> For sheaves to work effectively on given cpu, its NUMA node has to have
> struct node_barn allocated. Those are currently only allocated on nodes
> with memory (N_MEMORY) where kmem_cache_node also exist as the goal is
> to cache only node-local objects. But in order to have good performance
> on a memoryless node, we need its barn to exist and use sheaves to cache
> non-local objects (as no local objects can exist anyway).
>
> Therefore change the implementation to allocate barns on all online
> nodes, tracked in a new nodemask slab_barn_nodes. Also add a cpu hotplug
> callback as that's when a memoryless node can become online.
>
> Change rcu_sheaf->node assignment to numa_node_id() so it's returned to
> the barn of the local cpu's (potentially memoryless) node, and not to
> the nearest node with memory anymore.
>
> Reported-by: Ming Lei <ming.lei@redhat.com>
> Link: https://lore.kernel.org/all/aZ0SbIqaIkwoW2mB@fedora/
> Signed-off-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>
> ---

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

--
Cheers,
Harry / Hyeonggon