linux-kernel - Re: [PATCH 06/12] mm, slub: don't create kmalloc-rcl caches with CONFIG_SLUB

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Date:   Thu, 24 Nov 2022 22:23:44 +0900
From:   Hyeonggon Yoo <42.hyeyoo@...il.com>
To:     Vlastimil Babka <vbabka@...e.cz>
Cc:     Christoph Lameter <cl@...ux.com>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Pekka Enberg <penberg@...nel.org>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Matthew Wilcox <willy@...radead.org>, patches@...ts.linux.dev,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 06/12] mm, slub: don't create kmalloc-rcl caches with
 CONFIG_SLUB_TINY

On Wed, Nov 23, 2022 at 02:53:43PM +0100, Vlastimil Babka wrote:
> On 11/21/22 18:11, Vlastimil Babka wrote:
> > Distinguishing kmalloc(__GFP_RECLAIMABLE) can help against fragmentation
> > by grouping pages by mobility, but on tiny systems the extra memory
> > overhead of separate set of kmalloc-rcl caches will probably be worse,
> > and mobility grouping likely disabled anyway.
> > 
> > Thus with CONFIG_SLUB_TINY, don't create kmalloc-rcl caches and use the
> > regular ones.
> > 
> > Signed-off-by: Vlastimil Babka <vbabka@...e.cz>
> 
> Fixed up in response to lkp report for a MEMCG_KMEM+SLUB_TINY combo:
> ---8<---
> From c1ec0b924850a2863d061f316615d596176f15bb Mon Sep 17 00:00:00 2001
> From: Vlastimil Babka <vbabka@...e.cz>
> Date: Tue, 15 Nov 2022 18:19:28 +0100
> Subject: [PATCH 06/12] mm, slub: don't create kmalloc-rcl caches with
>  CONFIG_SLUB_TINY
> 
> Distinguishing kmalloc(__GFP_RECLAIMABLE) can help against fragmentation
> by grouping pages by mobility, but on tiny systems the extra memory
> overhead of separate set of kmalloc-rcl caches will probably be worse,
> and mobility grouping likely disabled anyway.
> 
> Thus with CONFIG_SLUB_TINY, don't create kmalloc-rcl caches and use the
> regular ones.
> 
> Signed-off-by: Vlastimil Babka <vbabka@...e.cz>
> ---
>  include/linux/slab.h |  9 +++++++--
>  mm/slab_common.c     | 10 ++++++++--
>  2 files changed, 15 insertions(+), 4 deletions(-)
> 
> diff --git a/include/linux/slab.h b/include/linux/slab.h
> index 45efc6c553b8..ae2d19ec8467 100644
> --- a/include/linux/slab.h
> +++ b/include/linux/slab.h
> @@ -336,12 +336,17 @@ enum kmalloc_cache_type {
>  #endif
>  #ifndef CONFIG_MEMCG_KMEM
>  	KMALLOC_CGROUP = KMALLOC_NORMAL,
> -#else
> -	KMALLOC_CGROUP,
>  #endif
> +#ifdef CONFIG_SLUB_TINY
> +	KMALLOC_RECLAIM = KMALLOC_NORMAL,
> +#else
>  	KMALLOC_RECLAIM,
> +#endif
>  #ifdef CONFIG_ZONE_DMA
>  	KMALLOC_DMA,
> +#endif
> +#ifdef CONFIG_MEMCG_KMEM
> +	KMALLOC_CGROUP,
>  #endif
>  	NR_KMALLOC_TYPES
>  };
> diff --git a/mm/slab_common.c b/mm/slab_common.c
> index a8cb5de255fc..907d52963806 100644
> --- a/mm/slab_common.c
> +++ b/mm/slab_common.c
> @@ -770,10 +770,16 @@ EXPORT_SYMBOL(kmalloc_size_roundup);
>  #define KMALLOC_CGROUP_NAME(sz)
>  #endif
>  
> +#ifndef CONFIG_SLUB_TINY
> +#define KMALLOC_RCL_NAME(sz)	.name[KMALLOC_RECLAIM] = "kmalloc-rcl-" #sz,
> +#else
> +#define KMALLOC_RCL_NAME(sz)
> +#endif
> +
>  #define INIT_KMALLOC_INFO(__size, __short_size)			\
>  {								\
>  	.name[KMALLOC_NORMAL]  = "kmalloc-" #__short_size,	\
> -	.name[KMALLOC_RECLAIM] = "kmalloc-rcl-" #__short_size,	\
> +	KMALLOC_RCL_NAME(__short_size)				\
>  	KMALLOC_CGROUP_NAME(__short_size)			\
>  	KMALLOC_DMA_NAME(__short_size)				\
>  	.size = __size,						\
> @@ -859,7 +865,7 @@ void __init setup_kmalloc_cache_index_table(void)
>  static void __init
>  new_kmalloc_cache(int idx, enum kmalloc_cache_type type, slab_flags_t flags)
>  {
> -	if (type == KMALLOC_RECLAIM) {
> +	if ((KMALLOC_RECLAIM != KMALLOC_NORMAL) && (type == KMALLOC_RECLAIM)) {

for consistency this can be:
	if (IS_ENABLED(CONFIG_SLUB_TINY) && (type == KMALLOC_RECLAIM)) {

But yeah, it's not a big deal.

>  		flags |= SLAB_RECLAIM_ACCOUNT;
>  	} else if (IS_ENABLED(CONFIG_MEMCG_KMEM) && (type == KMALLOC_CGROUP)) {
>  		if (mem_cgroup_kmem_disabled()) {
> -- 
> 2.38.1
> 

For either case:

Looks good to me.
Reviewed-by: Hyeonggon Yoo <42.hyeyoo@...il.com>

-- 
Thanks,
Hyeonggon