On 28/11/2025 12.37, Harry Yoo wrote:
> Currently, kvfree_rcu_barrier() flushes RCU sheaves across all slab
> caches when a cache is destroyed. This is unnecessary when destroying
> a slab cache; 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 and call it
> 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): 8529
> Total time (us): 162069
>
> After:
> Total calls: 19
> Average latency (us): 3804
> Total time (us): 72287
>
> Link:
> https://lore.kernel.org/linux-mm/[email protected]
> Link:
> https://lore.kernel.org/linux-mm/[email protected]
> Link:
> https://lore.kernel.org/linux-mm/[email protected]
> Suggested-by: Vlastimil Babka <[email protected]>
> Signed-off-by: Harry Yoo <[email protected]>
> ---
Thanks Harry for the patch,
A quick test on a different machine from the one I originally used to report
this shows a decrease from 214s to 100s.
LGTM,
Tested-by: Daniel Gomez <[email protected]>
>
> Not sure if the regression is worse on the reporters' machines due to
> higher core count (or because some cores were busy doing other things,
> dunno).
FWIW, CI modules run on an 8 core VM. Depending on the host CPU, this made the
absolute number different but equivalent performance degradation.
>
> Hopefully this will reduce the time to complete tests,
> and Suren could add his patch on top of this ;)
>
> include/linux/slab.h | 5 ++++
> mm/slab.h | 1 +
> mm/slab_common.c | 52 +++++++++++++++++++++++++++++------------
> mm/slub.c | 55 ++++++++++++++++++++++++--------------------
> 4 files changed, 73 insertions(+), 40 deletions(-)
