On Tue, 2011-11-22 at 02:36 +0800, Mel Gorman wrote: > This patch adds a lightweight sync migrate operation MIGRATE_SYNC_LIGHT > mode that avoids writing back pages to backing storage. Async > compaction maps to MIGRATE_ASYNC while sync compaction maps to > MIGRATE_SYNC_LIGHT. For other migrate_pages users such as memory > hotplug, MIGRATE_SYNC is used. > > This avoids sync compaction stalling for an excessive length of time, > particularly when copying files to a USB stick where there might be > a large number of dirty pages backed by a filesystem that does not > support ->writepages. Hi, from my understanding, with this, even writes to /proc/sys/vm/compact_memory doesn't wait for pageout, is this intended? on the other hand, MIGRATE_SYNC_LIGHT now waits for pagelock and buffer lock, so could wait on page read. page read and page out have the same latency, why takes them different? Thanks, Shaohua -- 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/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>