From: NeilBrown Date: Wed, 4 Jun 2014 23:07:42 +0000 (-0700) Subject: mm/vmscan.c: avoid throttling reclaim for loop-back nfsd threads X-Git-Tag: omap-for-v3.16/fixes-against-rc1~56^2~16^2~180 X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=399ba0b95670c70aaaa3f4f1623ea9e76c391681;p=pandora-kernel.git mm/vmscan.c: avoid throttling reclaim for loop-back nfsd threads When a loopback NFS mount is active and the backing device for the NFS mount becomes congested, that can impose throttling delays on the nfsd threads. These delays significantly reduce throughput and so the NFS mount remains congested. This results in a livelock and the reduced throughput persists. This livelock has been found in testing with the 'wait_iff_congested' call, and could possibly be caused by the 'congestion_wait' call. This livelock is similar to the deadlock which justified the introduction of PF_LESS_THROTTLE, and the same flag can be used to remove this livelock. To minimise the impact of the change, we still throttle nfsd when the filesystem it is writing to is congested, but not when some separate filesystem (e.g. the NFS filesystem) is congested. Signed-off-by: NeilBrown Cc: Mel Gorman Cc: Johannes Weiner Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- Reading git-diff-tree failed