linux-kernel - Re: [PATCH v3] mm: slub: only warn once when allocating slab obj extensions fails

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Message-ID: <5b0301cd-cc14-4dae-943a-6a300fb560d1@suse.cz>
Date: Mon, 26 May 2025 11:33:23 +0200
From: Vlastimil Babka <vbabka@...e.cz>
To: Usama Arif <usamaarif642@...il.com>,
 Andrew Morton <akpm@...ux-foundation.org>, surenb@...gle.com
Cc: hannes@...xchg.org, shakeel.butt@...ux.dev, vlad.wing@...il.com,
 linux-mm@...ck.org, kent.overstreet@...ux.dev, cl@...two.org,
 rientjes@...gle.com, roman.gushchin@...ux.dev, harry.yoo@...cle.com,
 linux-kernel@...r.kernel.org, kernel-team@...a.com
Subject: Re: [PATCH v3] mm: slub: only warn once when allocating slab obj
 extensions fails

On 5/23/25 18:52, Usama Arif wrote:
> In memory bound systems, a large number of warnings for failing this
> allocation repeatedly may mask any real issues in the system
> during memory pressure being reported in dmesg. Change this to
> warning only once.
> 
> Signed-off-by: Usama Arif <usamaarif642@...il.com>
> Reported-by: Vlad Poenaru <vlad.wing@...il.com>
> Closes: https://lore.kernel.org/all/17fab2d6-5a74-4573-bcc3-b75951508f0a@gmail.com/
> ---
> v2 -> v3:
> - Put warning back, but only warn once with pr_warn_once.
> v1 -> v2:
> - remove the warning completely. We will have a way in the
>   future to indicate that the mem alloc profile is inaccurate.
> ---
>  mm/slub.c | 8 +++++---
>  1 file changed, 5 insertions(+), 3 deletions(-)
> 
> diff --git a/mm/slub.c b/mm/slub.c
> index dc9e729e1d26..36d7c43a6f2a 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -2102,10 +2102,12 @@ prepare_slab_obj_exts_hook(struct kmem_cache *s, gfp_t flags, void *p)
>  
>  	slab = virt_to_slab(p);
>  	if (!slab_obj_exts(slab) &&
> -	    WARN(alloc_slab_obj_exts(slab, s, flags, false),
> -		 "%s, %s: Failed to create slab extension vector!\n",
> -		 __func__, s->name))
> +	    alloc_slab_obj_exts(slab, s, flags, false)) {
> +		pr_warn_once("%s, %s: Failed to create slab extension vector!\n",
> +			__func__, s->name);
>  		return NULL;
> +	}
> +

I've removed the extra line locally.

Added to slab/for-next, thanks.

>  
>  	return slab_obj_exts(slab) + obj_to_index(s, slab, p);
>  }