On Thu, Jul 14, 2011 at 09:41:50AM +1000, Dave Chinner wrote: > On Wed, Jul 13, 2011 at 03:31:25PM +0100, Mel Gorman wrote: > > Workloads that are allocating frequently and writing files place a > > large number of dirty pages on the LRU. With use-once logic, it is > > possible for them to reach the end of the LRU quickly requiring the > > reclaimer to scan more to find clean pages. Ordinarily, processes that > > are dirtying memory will get throttled by dirty balancing but this > > is a global heuristic and does not take into account that LRUs are > > maintained on a per-zone basis. This can lead to a situation whereby > > reclaim is scanning heavily, skipping over a large number of pages > > under writeback and recycling them around the LRU consuming CPU. > > > > This patch checks how many of the number of pages isolated from the > > LRU were dirty. If a percentage of them are dirty, the process will be > > throttled if a blocking device is congested or the zone being scanned > > is marked congested. The percentage that must be dirty depends on > > the priority. At default priority, all of them must be dirty. At > > DEF_PRIORITY-1, 50% of them must be dirty, DEF_PRIORITY-2, 25% > > etc. i.e. as pressure increases the greater the likelihood the process > > will get throttled to allow the flusher threads to make some progress. > > It still doesn't take into account how many pages under writeback > were skipped. If there are lots of pages that are under writeback, I > think we still want to throttle to give IO a chance to complete and > clean those pages before scanning again.... > An earlier revision did take them into account but in these tests at least, 0 pages at the end of the LRU were PageWriteback. I expect this to change when multiple processes and CPUs were in use but am ignoring it for the moment. -- Mel Gorman SUSE Labs _______________________________________________ xfs mailing list xfs@xxxxxxxxxxx http://oss.sgi.com/mailman/listinfo/xfs
