Re: [PATCH v3 02/21] slab: add SLAB_CONSISTENCY_CHECKS to SLAB_NEVER_MERGE

Suren Baghdasaryan
2026-01-16T17:22:49Z

On Fri, Jan 16, 2026 at 6:40 AM Vlastimil Babka <vbabka@suse.cz> wrote:
>
> All the debug flags prevent merging, except SLAB_CONSISTENCY_CHECKS. This
> is suboptimal because this flag (like any debug flags) prevents the
> usage of any fastpaths, and thus affect performance of any aliased
> cache. Also the objects from an aliased cache than the one specified for
> debugging could also interfere with the debugging efforts.
>
> Fix this by adding the whole SLAB_DEBUG_FLAGS collection to
> SLAB_NEVER_MERGE instead of individual debug flags, so it now also
> includes SLAB_CONSISTENCY_CHECKS.
>
> Signed-off-by: Vlastimil Babka <vbabka@suse.cz>

Reviewed-by: Suren Baghdasaryan <surenb@google.com>

> ---
> mm/slab_common.c | 5 ++---
> 1 file changed, 2 insertions(+), 3 deletions(-)
>
> diff --git a/mm/slab_common.c b/mm/slab_common.c
> index ee994ec7f251..e691ede0e6a8 100644
> --- a/mm/slab_common.c
> +++ b/mm/slab_common.c
> @@ -45,9 +45,8 @@ struct kmem_cache *kmem_cache;
> /*
> * Set of flags that will prevent slab merging
> */
> -#define SLAB_NEVER_MERGE (SLAB_RED_ZONE | SLAB_POISON | SLAB_STORE_USER | \
> - SLAB_TRACE | SLAB_TYPESAFE_BY_RCU | SLAB_NOLEAKTRACE | \
> - SLAB_FAILSLAB | SLAB_NO_MERGE)
> +#define SLAB_NEVER_MERGE (SLAB_DEBUG_FLAGS | SLAB_TYPESAFE_BY_RCU | \
> + SLAB_NOLEAKTRACE | SLAB_FAILSLAB | SLAB_NO_MERGE)
>
> #define SLAB_MERGE_SAME (SLAB_RECLAIM_ACCOUNT | SLAB_CACHE_DMA | \
> SLAB_CACHE_DMA32 | SLAB_ACCOUNT)
>
> --
> 2.52.0
>