On Mon, 2 Dec 2013, Joonsoo Kim wrote: > Currently, the freelist of a slab consist of unsigned int sized indexes. > Since most of slabs have less number of objects than 256, large sized > indexes is needless. For example, consider the minimum kmalloc slab. It's > object size is 32 byte and it would consist of one page, so 256 indexes > through byte sized index are enough to contain all possible indexes. > > There can be some slabs whose object size is 8 byte. We cannot handle > this case with byte sized index, so we need to restrict minimum > object size. Since these slabs are not major, wasted memory from these > slabs would be negligible. > > Some architectures' page size isn't 4096 bytes and rather larger than > 4096 bytes (One example is 64KB page size on PPC or IA64) so that > byte sized index doesn't fit to them. In this case, we will use > two bytes sized index. > > Below is some number for this patch. > > * Before * > 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 * > 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 11 more > objects, so 352 bytes (11 * 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. > > Here are the performance results on my 4 cpus machine. > > * Before * > > Performance counter stats for 'perf bench sched messaging -g 50 -l 1000' (10 runs): > > 229,945,138 cache-misses ( +- 0.23% ) > > 11.627897174 seconds time elapsed ( +- 0.14% ) > > * After * > > Performance counter stats for 'perf bench sched messaging -g 50 -l 1000' (10 runs): > > 218,640,472 cache-misses ( +- 0.42% ) > > 11.504999837 seconds time elapsed ( +- 0.21% ) > > cache-misses are reduced by this patchset, roughly 5%. > And elapsed times are improved by 1%. > > Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx> Acked-by: David Rientjes <rientjes@xxxxxxxxxx> -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>