On Mon, Aug 01, 2011 at 12:06:06AM +0900, Minchan Kim wrote: > On Thu, Jul 21, 2011 at 05:28:43PM +0100, Mel Gorman wrote: > > From: Mel Gorman <mel@xxxxxxxxx> > > > > When kswapd is failing to keep zones above the min watermark, a process > > will enter direct reclaim in the same manner kswapd does. If a dirty > > page is encountered during the scan, this page is written to backing > > storage using mapping->writepage. > > > > This causes two problems. First, it can result in very deep call > > stacks, particularly if the target storage or filesystem are complex. > > Some filesystems ignore write requests from direct reclaim as a result. > > The second is that a single-page flush is inefficient in terms of IO. > > While there is an expectation that the elevator will merge requests, > > this does not always happen. Quoting Christoph Hellwig; > > > > The elevator has a relatively small window it can operate on, > > and can never fix up a bad large scale writeback pattern. > > > > This patch prevents direct reclaim writing back filesystem pages by > > checking if current is kswapd. Anonymous pages are still written to > > swap as there is not the equivalent of a flusher thread for anonymous > > pages. If the dirty pages cannot be written back, they are placed > > back on the LRU lists. There is now a direct dependency on dirty page > > balancing to prevent too many pages in the system being dirtied which > > would prevent reclaim making forward progress. > > > > Signed-off-by: Mel Gorman <mgorman@xxxxxxx> > Reviewed-by: Minchan Kim <minchan.kim@xxxxxxxxx> > Thanks > Nitpick. > We can change description of should_reclaim_stall. > > "Returns true if the caller should wait to clean dirty/writeback pages" > -> > "Returns true if direct reclaimer should wait to clean writeback pages" > Not a nitpick. At least one check for RECLAIM_MODE_SYNC is no longer reachable. I've added a new patch that updates the comment and has synchronous direct reclaim wait on pages under writeback. -- Mel Gorman SUSE Labs -- 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>