linux-kernel - Re: [PATCH v3 02/21] slab: add SLAB_CONSISTENCY_CHECKS to SLAB_NEVER

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Message-ID: <CAJuCfpG0SCGf-TOTRi0d8e0Zoh4r5-xXByhnmJRSiyUt9=LO4w@mail.gmail.com>
Date: Fri, 16 Jan 2026 09:22:34 -0800
From: Suren Baghdasaryan <surenb@...gle.com>
To: Vlastimil Babka <vbabka@...e.cz>
Cc: Harry Yoo <harry.yoo@...cle.com>, Petr Tesarik <ptesarik@...e.com>, 
	Christoph Lameter <cl@...two.org>, David Rientjes <rientjes@...gle.com>, 
	Roman Gushchin <roman.gushchin@...ux.dev>, Hao Li <hao.li@...ux.dev>, 
	Andrew Morton <akpm@...ux-foundation.org>, Uladzislau Rezki <urezki@...il.com>, 
	"Liam R. Howlett" <Liam.Howlett@...cle.com>, Sebastian Andrzej Siewior <bigeasy@...utronix.de>, 
	Alexei Starovoitov <ast@...nel.org>, linux-mm@...ck.org, linux-kernel@...r.kernel.org, 
	linux-rt-devel@...ts.linux.dev, bpf@...r.kernel.org, 
	kasan-dev@...glegroups.com
Subject: Re: [PATCH v3 02/21] slab: add SLAB_CONSISTENCY_CHECKS to SLAB_NEVER_MERGE

On Fri, Jan 16, 2026 at 6:40 AM Vlastimil Babka <vbabka@...e.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@...e.cz>

Reviewed-by: Suren Baghdasaryan <surenb@...gle.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
>