Re: [PATCH V2] mm/slab: introduce kvfree_rcu_barrier_on_cache() for cache destruction

[Harry Yoo <harry.yoo@oracle.com>]

On Tue, Dec 02, 2025 at 07:16:26PM +0900, Harry Yoo wrote:
> Currently, kvfree_rcu_barrier() flushes RCU sheaves across all slab
> caches when a cache is destroyed. This is unnecessary; only the RCU
> sheaves belonging to the cache being destroyed need to be flushed.
> 
> As suggested by Vlastimil Babka, introduce a weaker form of
> kvfree_rcu_barrier() that operates on a specific slab cache.
> 
> Factor out flush_rcu_sheaves_on_cache() from flush_all_rcu_sheaves() and
> call it from flush_all_rcu_sheaves() and kvfree_rcu_barrier_on_cache().
> 
> Call kvfree_rcu_barrier_on_cache() instead of kvfree_rcu_barrier() on
> cache destruction.
> 
> The performance benefit is evaluated on a 12 core 24 threads AMD Ryzen
> 5900X machine (1 socket), by loading slub_kunit module.
> 
> Before:
>   Total calls: 19
>   Average latency (us): 18127
>   Total time (us): 344414
> 
> After:
>   Total calls: 19
>   Average latency (us): 10066
>   Total time (us): 191264
> 
> Two performance regression have been reported:
>   - stress module loader test's runtime increases by 50-60% (Daniel)
>   - internal graphics test's runtime on Tegra23 increases by 35% (Jon)
                                         ^Tegra234

					 just a minor typo :)

> 
> They are fixed by this change.
> 
> Suggested-by: Vlastimil Babka <vbabka@suse.cz>
> Fixes: ec66e0d59952 ("slab: add sheaf support for batching kfree_rcu() operations")
> Cc: <stable@vger.kernel.org>
> Link: https://lore.kernel.org/linux-mm/1bda09da-93be-4737-aef0-d47f8c5c9301@suse.cz
> Reported-and-tested-by: Daniel Gomez <da.gomez@samsung.com>
> Closes: https://lore.kernel.org/linux-mm/0406562e-2066-4cf8-9902-b2b0616dd742@kernel.org
> Reported-and-tested-by: Jon Hunter <jonathanh@nvidia.com>
> Closes: https://lore.kernel.org/linux-mm/e988eff6-1287-425e-a06c-805af5bbf262@nvidia.com
> Signed-off-by: Harry Yoo <harry.yoo@oracle.com>
> ---

-- 
Cheers,
Harry / Hyeonggon