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> 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" -- Kind regards, Minchan Kim _______________________________________________ xfs mailing list xfs@xxxxxxxxxxx http://oss.sgi.com/mailman/listinfo/xfs
