mm, slab/slub: introduce kmalloc-reclaimable caches

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.

Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Vlastimil Babka <[email protected]>
Acked-by: Mel Gorman <[email protected]>
Acked-by: Christoph Lameter <[email protected]>
Acked-by: Roman Gushchin <[email protected]>
Cc: David Rientjes <[email protected]>
Cc: Johannes Weiner <[email protected]>
Cc: Joonsoo Kim <[email protected]>
Cc: Laura Abbott <[email protected]>
Cc: Matthew Wilcox <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Sumit Semwal <[email protected]>
Cc: Vijayanand Jitta <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

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