[PATCH v8 04/23] slab: add sheaf support for batching kfree_rcu() operations

[Vlastimil Babka]

On 9/25/25 06:35, Suren Baghdasaryan wrote:
> On Thu, Sep 18, 2025 at 1:09 AM Vlastimil Babka <vbabka at suse.cz> wrote:
>>
>> Expected advantages:
>> - batching the kfree_rcu() operations, that could eventually replace the
>>   existing batching
>> - sheaves can be reused for allocations via barn instead of being
>>   flushed to slabs, which is more efficient
>>   - this includes cases where only some cpus are allowed to process rcu
>>     callbacks (Android)
> 
> nit: I would say it's more CONFIG_RCU_NOCB_CPU related. Android is
> just an instance of that.

OK changed that.

Changes due to your other suggestions:

diff --git a/mm/slub.c b/mm/slub.c
index 8220ce095970..fec0cdc7ef37 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -3945,15 +3945,12 @@ void flush_all_rcu_sheaves(void)
                         */
 
                        INIT_WORK(&sfw->work, flush_rcu_sheaf);
-                       sfw->skip = false;
                        sfw->s = s;
                        queue_work_on(cpu, flushwq, &sfw->work);
                }
 
                for_each_online_cpu(cpu) {
                        sfw = &per_cpu(slub_flush, cpu);
-                       if (sfw->skip)
-                               continue;
                        flush_work(&sfw->work);
                }
 
@@ -5643,6 +5640,10 @@ bool __kfree_rcu_sheaf(struct kmem_cache *s, void *obj)
 
        rcu_sheaf = pcs->rcu_free;
 
+       /*
+        * Since we flush immediately when size reaches capacity, we never reach
+        * this with size already at capacity, so no OOB write is possible.
+        */
        rcu_sheaf->objects[rcu_sheaf->size++] = obj;
 
        if (likely(rcu_sheaf->size < s->sheaf_capacity))