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Date: Mon, 2 Sep 2013 17:38:54 +0900 From: Joonsoo Kim <iamjoonsoo.kim@....com> To: Pekka Enberg <penberg@...nel.org> Cc: Christoph Lameter <cl@...ux.com>, Andrew Morton <akpm@...ux-foundation.org>, Joonsoo Kim <js1304@...il.com>, David Rientjes <rientjes@...gle.com>, linux-mm@...ck.org, linux-kernel@...r.kernel.org, Joonsoo Kim <iamjoonsoo.kim@....com> Subject: [PATCH 0/4] slab: implement byte sized indexes for the freelist of a slab This patchset implements byte sized indexes for the freelist of a slab. Currently, the freelist of a slab consist of unsigned int sized indexes. Most of slabs have less number of objects than 256, so much space is wasted. To reduce this overhead, this patchset implements byte sized indexes for the freelist of a slab. With it, we can save 3 bytes for each objects. This introduce one likely branch to functions used for setting/getting objects to/from the freelist, but we may get more benefits from this change. Below is some numbers of 'cat /proc/slabinfo' related to my previous posting and this patchset. * Before * # name <active_objs> <num_objs> <objsize> <objperslab> <pagesperslab> : tunables [snip...] kmalloc-512 525 640 512 8 1 : tunables 54 27 0 : slabdata 80 80 0 kmalloc-256 210 210 256 15 1 : tunables 120 60 0 : slabdata 14 14 0 kmalloc-192 1016 1040 192 20 1 : tunables 120 60 0 : slabdata 52 52 0 kmalloc-96 560 620 128 31 1 : tunables 120 60 0 : slabdata 20 20 0 kmalloc-64 2148 2280 64 60 1 : tunables 120 60 0 : slabdata 38 38 0 kmalloc-128 647 682 128 31 1 : tunables 120 60 0 : slabdata 22 22 0 kmalloc-32 11360 11413 32 113 1 : tunables 120 60 0 : slabdata 101 101 0 kmem_cache 197 200 192 20 1 : tunables 120 60 0 : slabdata 10 10 0 * After my previous posting(overload struct slab over struct page) * # name <active_objs> <num_objs> <objsize> <objperslab> <pagesperslab> : tunables [snip...] kmalloc-512 527 600 512 8 1 : tunables 54 27 0 : slabdata 75 75 0 kmalloc-256 210 210 256 15 1 : tunables 120 60 0 : slabdata 14 14 0 kmalloc-192 1040 1040 192 20 1 : tunables 120 60 0 : slabdata 52 52 0 kmalloc-96 750 750 128 30 1 : tunables 120 60 0 : slabdata 25 25 0 kmalloc-64 2773 2773 64 59 1 : tunables 120 60 0 : slabdata 47 47 0 kmalloc-128 660 690 128 30 1 : tunables 120 60 0 : slabdata 23 23 0 kmalloc-32 11200 11200 32 112 1 : tunables 120 60 0 : slabdata 100 100 0 kmem_cache 197 200 192 20 1 : tunables 120 60 0 : slabdata 10 10 0 kmem_caches consisting of objects less than or equal to 128 byte have one more objects in a slab. You can see it at objperslab. We can improve further with this patchset. * My previous posting + this patchset * # name <active_objs> <num_objs> <objsize> <objperslab> <pagesperslab> : tunables [snip...] kmalloc-512 521 648 512 8 1 : tunables 54 27 0 : slabdata 81 81 0 kmalloc-256 208 208 256 16 1 : tunables 120 60 0 : slabdata 13 13 0 kmalloc-192 1029 1029 192 21 1 : tunables 120 60 0 : slabdata 49 49 0 kmalloc-96 529 589 128 31 1 : tunables 120 60 0 : slabdata 19 19 0 kmalloc-64 2142 2142 64 63 1 : tunables 120 60 0 : slabdata 34 34 0 kmalloc-128 660 682 128 31 1 : tunables 120 60 0 : slabdata 22 22 0 kmalloc-32 11716 11780 32 124 1 : tunables 120 60 0 : slabdata 95 95 0 kmem_cache 197 210 192 21 1 : tunables 120 60 0 : slabdata 10 10 0 kmem_caches consisting of objects less than or equal to 256 byte have one or more objects than before. In the case of kmalloc-32, we have 12 more objects, so 384 bytes (12 * 32) are saved and this is roughly 9% saving of memory. Of couse, this percentage decreases as the number of objects in a slab decreases. Please let me know expert's opions :) Thanks. This patchset comes from a Christoph's idea. https://lkml.org/lkml/2013/8/23/315 Patches are on top of my previous posting. https://lkml.org/lkml/2013/8/22/137 Joonsoo Kim (4): slab: factor out calculate nr objects in cache_estimate slab: introduce helper functions to get/set free object slab: introduce byte sized index for the freelist of a slab slab: make more slab management structure off the slab mm/slab.c | 138 +++++++++++++++++++++++++++++++++++++++++++++---------------- 1 file changed, 103 insertions(+), 35 deletions(-) -- 1.7.9.5 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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