-
Mel Gorman authored
Due to either a fast search of the free list or a linear scan, it is possible for multiple compaction instances to pick the same pageblock for migration. This is lucky for one scanner and increased scanning for all the others. It also allows a race between requests on which first allocates the resulting free block. This patch tests and updates the pageblock skip for the migration scanner carefully. When isolating a block, it will check and skip if the block is already in use. Once the zone lock is acquired, it will be rechecked so that only one scanner can set the pageblock skip for exclusive use. Any scanner contending will continue with a linear scan. The skip bit is still set if no pages can be isolated in a range. While this may result in redundant scanning, it avoids unnecessarily acquiring the zone lock when there are no suitable migration sources. 1-socket thpscale Amean fault-both-1 0.00 ( 0.00%) 0.00 * 0.00%* Amean fault-both-3 3390.40 ( 0.00%) 3024.41 ( 10.80%) Amean fault-both-5 5082.28 ( 0.00%) 4749.30 ( 6.55%) Amean fault-both-7 7012.51 ( 0.00%) 6454.95 ( 7.95%) Amean fault-both-12 11346.63 ( 0.00%) 10324.83 ( 9.01%) Amean fault-both-18 15324.19 ( 0.00%) 12896.82 * 15.84%* Amean fault-both-24 16088.50 ( 0.00%) 13470.60 * 16.27%* Amean fault-both-30 18723.42 ( 0.00%) 17143.99 ( 8.44%) Amean fault-both-32 18612.01 ( 0.00%) 17743.91 ( 4.66%) 5.0.0-rc1 5.0.0-rc1 findmig-v3r15 isolmig-v3r15 Percentage huge-3 89.83 ( 0.00%) 92.96 ( 3.48%) Percentage huge-5 91.96 ( 0.00%) 93.26 ( 1.41%) Percentage huge-7 92.85 ( 0.00%) 93.63 ( 0.84%) Percentage huge-12 92.74 ( 0.00%) 92.80 ( 0.07%) Percentage huge-18 91.71 ( 0.00%) 91.62 ( -0.10%) Percentage huge-24 92.13 ( 0.00%) 91.50 ( -0.69%) Percentage huge-30 93.79 ( 0.00%) 92.73 ( -1.13%) Percentage huge-32 91.27 ( 0.00%) 91.94 ( 0.74%) This shows a reasonable reduction in latency as multiple compaction scanners do not operate on the same blocks with a similar allocation success rate. Compaction migrate scanned 41093126 25646769 Migration scan rates are reduced by 38%. Link: http://lkml.kernel.org/r/20190118175136.31341-11-mgorman@techsingularity.netSigned-off-by:
Mel Gorman <mgorman@techsingularity.net> Acked-by:
Vlastimil Babka <vbabka@suse.cz> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: Dan Carpenter <dan.carpenter@oracle.com> Cc: David Rientjes <rientjes@google.com> Cc: YueHaibing <yuehaibing@huawei.com> Signed-off-by:
Andrew Morton <akpm@linux-foundation.org> Signed-off-by:
Linus Torvalds <torvalds@linux-foundation.org>
e380bebe