[v3] slab: replace cpu (partial) slabs with sheaves

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

Posted by Vlastimil Babka 3 weeks, 3 days ago

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>
---
 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

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

Posted by Harry Yoo 3 weeks, 1 day ago

On Fri, Jan 16, 2026 at 03:40:22PM +0100, Vlastimil Babka 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: Harry Yoo <harry.yoo@oracle.com>

-- 
Cheers,
Harry / Hyeonggon

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

Posted by Suren Baghdasaryan 3 weeks, 3 days ago

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
>