linux-kernel - Re: [PATCH 1/2] mm: slub: allocate slab object extensions non-contiguously

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Message-ID: <3divtzm4iapcxwbzxlmfmg3gus75n3rqh43vkjnog456jm2k34@f3rpzvcfk3p6>
Date: Tue, 20 May 2025 09:44:01 -0400
From: Kent Overstreet <kent.overstreet@...ux.dev>
To: Usama Arif <usamaarif642@...il.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>, surenb@...gle.com, 
	hannes@...xchg.org, shakeel.butt@...ux.dev, vlad.wing@...il.com, linux-mm@...ck.org, 
	linux-kernel@...r.kernel.org, kernel-team@...a.com
Subject: Re: [PATCH 1/2] mm: slub: allocate slab object extensions
 non-contiguously

On Tue, May 20, 2025 at 01:25:46PM +0100, Usama Arif wrote:
> When memory allocation profiling is running on memory bound services,
> allocations greater than order 0 for slab object extensions can fail,
> for e.g. zs_handle zswap slab which will be 512 objsperslab x 16 bytes
> per slabobj_ext (order 1 allocation). Use kvcalloc to improve chances
> of the allocation being successful.
> 
> 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/
> ---
>  mm/slub.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/slub.c b/mm/slub.c
> index dc9e729e1d26..bf43c403ead2 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -1989,7 +1989,7 @@ int alloc_slab_obj_exts(struct slab *slab, struct kmem_cache *s,
>  	gfp &= ~OBJCGS_CLEAR_MASK;
>  	/* Prevent recursive extension vector allocation */
>  	gfp |= __GFP_NO_OBJ_EXT;
> -	vec = kcalloc_node(objects, sizeof(struct slabobj_ext), gfp,
> +	vec = kvcalloc_node(objects, sizeof(struct slabobj_ext), gfp,
>  			   slab_nid(slab));

And what's the latency going to be on a vmalloc() allocation when we're
low on memory?