Patch series "kmalloc-reclaimable caches", v4.

As discussed at LSF/MM [1] here's a patchset that introduces
kmalloc-reclaimable caches (more details in the second patch) and uses
them for dcache external names.  That allows us to repurpose the
NR_INDIRECTLY_RECLAIMABLE_BYTES counter later in the series.

With patch 3/6, dcache external names are allocated from kmalloc-rcl-*
caches, eliminating the need for manual accounting.  More importantly, it
also ensures the reclaimable kmalloc allocations are grouped in pages
separate from the regular kmalloc allocations.  The need for proper
accounting of dcache external names has shown it's easy for misbehaving
process to allocate lots of them, causing premature OOMs.  Without the
added grouping, it's likely that a similar workload can interleave the
dcache external names allocations with regular kmalloc allocations (note:
I haven't searched myself for an example of such regular kmalloc
allocation, but I would be very surprised if there wasn't some).  A
pathological case would be e.g.  one 64byte regular allocations with 63
external dcache names in a page (64x64=4096), which means the page is not
freed even after reclaiming after all dcache names, and the process can
thus "steal" the whole page with single 64byte allocation.

If other kmalloc users similar to dcache external names become identified,
they can also benefit from the new functionality simply by adding
__GFP_RECLAIMABLE to the kmalloc calls.

Side benefits of the patchset (that could be also merged separately)
include removed branch for detecting __GFP_DMA kmalloc(), and shortening
kmalloc cache names in /proc/slabinfo output.  The latter is potentially
an ABI break in case there are tools parsing the names and expecting the
values to be in bytes.

This is how /proc/slabinfo looks like after booting in virtme:

...
kmalloc-rcl-4M         0      0 4194304    1 1024 : tunables    1    1    0 : slabdata      0      0      0
...
kmalloc-rcl-96         7     32    128   32    1 : tunables  120   60    8 : slabdata      1      1      0
kmalloc-rcl-64        25    128     64   64    1 : tunables  120   60    8 : slabdata      2      2      0
kmalloc-rcl-32         0      0     32  124    1 : tunables  120   60    8 : slabdata      0      0      0
kmalloc-4M             0      0 4194304    1 1024 : tunables    1    1    0 : slabdata      0      0      0
kmalloc-2M             0      0 2097152    1  512 : tunables    1    1    0 : slabdata      0      0      0
kmalloc-1M             0      0 1048576    1  256 : tunables    1    1    0 : slabdata      0      0      0
...

/proc/vmstat with renamed nr_indirectly_reclaimable_bytes counter:

...
nr_slab_reclaimable 2817
nr_slab_unreclaimable 1781
...
nr_kernel_misc_reclaimable 0
...

/proc/meminfo with new KReclaimable counter:

...
Shmem:               564 kB
KReclaimable:      11260 kB
Slab:              18368 kB
SReclaimable:      11260 kB
SUnreclaim:         7108 kB
KernelStack:        1248 kB
...

This patch (of 6):

The kmalloc caches currently mainain separate (optional) array
kmalloc_dma_caches for __GFP_DMA allocations.  There are tests for
__GFP_DMA in the allocation hotpaths.  We can avoid the branches by
combining kmalloc_caches and kmalloc_dma_caches into a single
two-dimensional array where the outer dimension is cache "type".  This
will also allow to add kmalloc-reclaimable caches as a third type.

Link: http://lkml.kernel.org/r/20180731090649.16028-2-vbabka@suse.czSigned-off-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Mel Gorman <mgorman@techsingularity.net>
Acked-by: Christoph Lameter <cl@linux.com>
Acked-by: Roman Gushchin <guro@fb.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Laura Abbott <labbott@redhat.com>
Cc: Sumit Semwal <sumit.semwal@linaro.org>
Cc: Vijayanand Jitta <vjitta@codeaurora.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>