From: Vlastimil Babka Date: Wed, 4 Jun 2014 23:10:41 +0000 (-0700) Subject: mm, compaction: properly signal and act upon lock and need_sched() contention X-Git-Tag: omap-for-v3.16/fixes-against-rc1~56^2~16^2~96 X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=be9765722e6b7ece8263cbab857490332339bd6f;p=pandora-kernel.git mm, compaction: properly signal and act upon lock and need_sched() contention Compaction uses compact_checklock_irqsave() function to periodically check for lock contention and need_resched() to either abort async compaction, or to free the lock, schedule and retake the lock. When aborting, cc->contended is set to signal the contended state to the caller. Two problems have been identified in this mechanism. First, compaction also calls directly cond_resched() in both scanners when no lock is yet taken. This call either does not abort async compaction, or set cc->contended appropriately. This patch introduces a new compact_should_abort() function to achieve both. In isolate_freepages(), the check frequency is reduced to once by SWAP_CLUSTER_MAX pageblocks to match what the migration scanner does in the preliminary page checks. In case a pageblock is found suitable for calling isolate_freepages_block(), the checks within there are done on higher frequency. Second, isolate_freepages() does not check if isolate_freepages_block() aborted due to contention, and advances to the next pageblock. This violates the principle of aborting on contention, and might result in pageblocks not being scanned completely, since the scanning cursor is advanced. This problem has been noticed in the code by Joonsoo Kim when reviewing related patches. This patch makes isolate_freepages_block() check the cc->contended flag and abort. In case isolate_freepages() has already isolated some pages before aborting due to contention, page migration will proceed, which is OK since we do not want to waste the work that has been done, and page migration has own checks for contention. However, we do not want another isolation attempt by either of the scanners, so cc->contended flag check is added also to compaction_alloc() and compact_finished() to make sure compaction is aborted right after the migration. The outcome of the patch should be reduced lock contention by async compaction and lower latencies for higher-order allocations where direct compaction is involved. [akpm@linux-foundation.org: fix typo in comment] Reported-by: Joonsoo Kim Signed-off-by: Vlastimil Babka Reviewed-by: Naoya Horiguchi Cc: Minchan Kim Cc: Mel Gorman Cc: Bartlomiej Zolnierkiewicz Cc: Michal Nazarewicz Cc: Christoph Lameter Cc: Rik van Riel Acked-by: Michal Nazarewicz Tested-by: Shawn Guo Tested-by: Kevin Hilman Tested-by: Stephen Warren Tested-by: Fabio Estevam Cc: David Rientjes Cc: Stephen Rothwell Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- Reading git-diff-tree failed