linux-kernel - Re: [PATCH] mm/slab_common: move dma-kmalloc caches creation into new_kmalloc

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Date:   Sun, 10 Apr 2022 15:51:57 +0900
From:   Hyeonggon Yoo <42.hyeyoo@...il.com>
To:     Ohhoon Kwon <ohkwon1043@...il.com>
Cc:     Christoph Lameter <cl@...ux.com>,
        Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Roman Gushchin <roman.gushchin@...ux.dev>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Jiyoup Kim <lakroforce@...il.com>,
        Wonhyuk Yang <vvghjk1234@...il.com>,
        Donghyeok Kim <dthex5d@...il.com>,
        JaeSang Yoo <jsyoo5b@...il.com>
Subject: Re: [PATCH] mm/slab_common: move dma-kmalloc caches creation into
 new_kmalloc_cache()

On Sat, Apr 09, 2022 at 06:53:05PM +0900, Ohhoon Kwon wrote:
> There are four types of kmalloc_caches: KMALLOC_NORMAL, KMALLOC_CGROUP,
> KMALLOC_RECLAIM, and KMALLOC_DMA. While the first three types are
> created using new_kmalloc_cache(), KMALLOC_DMA caches are created in a
> separate logic. Let KMALLOC_DMA caches be also created using
> new_kmalloc_cache(), to enhance readability.
> 
> Historically, there were only KMALLOC_NORMAL caches and KMALLOC_DMA
> caches in the first place, and they were initialized in two separate
> logics. However, when KMALLOC_RECLAIM was introduced in v4.20 via
> commit 1291523f2c1d ("mm, slab/slub: introduce kmalloc-reclaimable
> caches") and KMALLOC_CGROUP was introduced in v5.14 via
> commit 494c1dfe855e ("mm: memcg/slab: create a new set of kmalloc-cg-<n>
> caches"), their creations were merged with KMALLOC_NORMAL's only.
> KMALLOC_DMA creation logic should be merged with them, too.
> 
> By merging KMALLOC_DMA initialization with other types, the following
> two changes might occur:
> 1. The order dma-kmalloc-<n> caches added in slab_cache list may be
> sorted by size. i.e. the order they appear in /proc/slabinfo may change
> as well.
> 2. slab_state will be set to UP after KMALLOC_DMA is created.
> In case of slub, freelist randomization is dependent on slab_state>=UP,
> and therefore KMALLOC_DMA cache's freelist will not be randomized in
> creation, but will be deferred to init_freelist_randomization().
> 
> Co-developed-by: JaeSang Yoo <jsyoo5b@...il.com>
> Signed-off-by: JaeSang Yoo <jsyoo5b@...il.com>
> Signed-off-by: Ohhoon Kwon <ohkwon1043@...il.com>
> ---
>  mm/slab_common.c | 20 +++++---------------
>  1 file changed, 5 insertions(+), 15 deletions(-)
> 
> diff --git a/mm/slab_common.c b/mm/slab_common.c
> index 6ee64d6208b3..eb95512de983 100644
> --- a/mm/slab_common.c
> +++ b/mm/slab_common.c
> @@ -849,6 +849,10 @@ new_kmalloc_cache(int idx, enum kmalloc_cache_type type, slab_flags_t flags)
>  			return;
>  		}
>  		flags |= SLAB_ACCOUNT;
> +#ifdef CONFIG_ZONE_DMA
> +	} else if (type == KMALLOC_DMA) {
> +		flags |= SLAB_CACHE_DMA;
> +#endif

Maybe IS_ENABLED() would be better instead of ifdef for consistency?

>  	}
>  
>  	kmalloc_caches[type][idx] = create_kmalloc_cache(
> @@ -877,7 +881,7 @@ void __init create_kmalloc_caches(slab_flags_t flags)
>  	/*
>  	 * Including KMALLOC_CGROUP if CONFIG_MEMCG_KMEM defined
>  	 */
> -	for (type = KMALLOC_NORMAL; type <= KMALLOC_RECLAIM; type++) {
> +	for (type = KMALLOC_NORMAL; type < NR_KMALLOC_TYPES; type++) {
>  		for (i = KMALLOC_SHIFT_LOW; i <= KMALLOC_SHIFT_HIGH; i++) {
>  			if (!kmalloc_caches[type][i])
>  				new_kmalloc_cache(i, type, flags);
> @@ -898,20 +902,6 @@ void __init create_kmalloc_caches(slab_flags_t flags)
>  
>  	/* Kmalloc array is now usable */
>  	slab_state = UP;
> -
> -#ifdef CONFIG_ZONE_DMA
> -	for (i = 0; i <= KMALLOC_SHIFT_HIGH; i++) {
> -		struct kmem_cache *s = kmalloc_caches[KMALLOC_NORMAL][i];
> -
> -		if (s) {
> -			kmalloc_caches[KMALLOC_DMA][i] = create_kmalloc_cache(
> -				kmalloc_info[i].name[KMALLOC_DMA],
> -				kmalloc_info[i].size,
> -				SLAB_CACHE_DMA | flags, 0,
> -				kmalloc_info[i].size);
> -		}
> -	}
> -#endif
>  }
>  #endif /* !CONFIG_SLOB */

The patch overall looks good to me.

Reviewed-by: Hyeonggon Yoo <42.hyeyoo@...il.com>

Thanks!

> -- 
> 2.25.1
> 
> 

-- 
Thanks,
Hyeonggon