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SubjectRe: [PATCH v3 2/7] mm, slab/slub: introduce kmalloc-reclaimable caches
On Wed, Jul 18, 2018 at 03:36:15PM +0200, Vlastimil Babka wrote:
> Kmem caches can be created with a SLAB_RECLAIM_ACCOUNT flag, which indicates
> they contain objects which can be reclaimed under memory pressure (typically
> through a shrinker). This makes the slab pages accounted as NR_SLAB_RECLAIMABLE
> in vmstat, which is reflected also the MemAvailable meminfo counter and in
> overcommit decisions. The slab pages are also allocated with __GFP_RECLAIMABLE,
> which is good for anti-fragmentation through grouping pages by mobility.
>
> The generic kmalloc-X caches are created without this flag, but sometimes are
> used also for objects that can be reclaimed, which due to varying size cannot
> have a dedicated kmem cache with SLAB_RECLAIM_ACCOUNT flag. A prominent example
> are dcache external names, which prompted the creation of a new, manually
> managed vmstat counter NR_INDIRECTLY_RECLAIMABLE_BYTES in commit f1782c9bc547
> ("dcache: account external names as indirectly reclaimable memory").
>
> To better handle this and any other similar cases, this patch introduces
> SLAB_RECLAIM_ACCOUNT variants of kmalloc caches, named kmalloc-rcl-X.
> They are used whenever the kmalloc() call passes __GFP_RECLAIMABLE among gfp
> flags. They are added to the kmalloc_caches array as a new type. Allocations
> with both __GFP_DMA and __GFP_RECLAIMABLE will use a dma type cache.
>
> This change only applies to SLAB and SLUB, not SLOB. This is fine, since SLOB's
> target are tiny system and this patch does add some overhead of kmem management
> objects.
>
> Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
> ---
> include/linux/slab.h | 16 +++++++++++----
> mm/slab_common.c | 48 ++++++++++++++++++++++++++++----------------
> 2 files changed, 43 insertions(+), 21 deletions(-)
>
> diff --git a/include/linux/slab.h b/include/linux/slab.h
> index 4299c59353a1..d89e934e0d8b 100644
> --- a/include/linux/slab.h
> +++ b/include/linux/slab.h
> @@ -296,11 +296,12 @@ static inline void __check_heap_object(const void *ptr, unsigned long n,
> (KMALLOC_MIN_SIZE) : 16)
>
> #define KMALLOC_NORMAL 0
> +#define KMALLOC_RECLAIM 1
> #ifdef CONFIG_ZONE_DMA
> -#define KMALLOC_DMA 1
> -#define KMALLOC_TYPES 2
> +#define KMALLOC_DMA 2
> +#define KMALLOC_TYPES 3
> #else
> -#define KMALLOC_TYPES 1
> +#define KMALLOC_TYPES 2
> #endif
>
> #ifndef CONFIG_SLOB
> @@ -309,12 +310,19 @@ extern struct kmem_cache *kmalloc_caches[KMALLOC_TYPES][KMALLOC_SHIFT_HIGH + 1];
> static __always_inline unsigned int kmalloc_type(gfp_t flags)
> {
> int is_dma = 0;
> + int is_reclaimable;
>
> #ifdef CONFIG_ZONE_DMA
> is_dma = !!(flags & __GFP_DMA);
> #endif
>
> - return is_dma;
> + is_reclaimable = !!(flags & __GFP_RECLAIMABLE);
> +
> + /*
> + * If an allocation is botth __GFP_DMA and __GFP_RECLAIMABLE, return
^^
typo
> + * KMALLOC_DMA and effectively ignore __GFP_RECLAIMABLE
> + */
> + return (is_dma * 2) + (is_reclaimable & !is_dma);

Maybe
is_dma * KMALLOC_DMA + (is_reclaimable && !is_dma) * KMALLOC_RECLAIM
looks better?

> }
>
> /*
> diff --git a/mm/slab_common.c b/mm/slab_common.c
> index 4614248ca381..614fb7ab8312 100644
> --- a/mm/slab_common.c
> +++ b/mm/slab_common.c
> @@ -1107,10 +1107,21 @@ void __init setup_kmalloc_cache_index_table(void)
> }
> }
>
> -static void __init new_kmalloc_cache(int idx, slab_flags_t flags)
> +static void __init
> +new_kmalloc_cache(int idx, int type, slab_flags_t flags)
> {
> - kmalloc_caches[KMALLOC_NORMAL][idx] = create_kmalloc_cache(
> - kmalloc_info[idx].name,
> + const char *name;
> +
> + if (type == KMALLOC_RECLAIM) {
> + flags |= SLAB_RECLAIM_ACCOUNT;
> + name = kasprintf(GFP_NOWAIT, "kmalloc-rcl-%u",
> + kmalloc_info[idx].size);
> + BUG_ON(!name);

I'd replace this with WARN_ON() and falling back to kmalloc_info[idx].name.

> + } else {
> + name = kmalloc_info[idx].name;
> + }
> +
> + kmalloc_caches[type][idx] = create_kmalloc_cache(name,
> kmalloc_info[idx].size, flags, 0,
> kmalloc_info[idx].size);
> }

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