On Wed, 10 Aug 2011 11:47:19 +0100 Mel Gorman <mgorman@xxxxxxx> 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 and under writeback. If a percentage of them under > writeback, the process will be throttled if a backing device or the > zone is congested. Note that this applies whether it is anonymous or > file-backed pages that are under writeback meaning that swapping is > potentially throttled. This is intentional due to the fact if the > swap device is congested, scanning more pages and dispatching more > IO is not going to help matters. > > The percentage that must be in writeback depends on the priority. At > default priority, all of them must be dirty. At DEF_PRIORITY-1, 50% > of them must be, 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. > > Signed-off-by: Mel Gorman <mgorman@xxxxxxx> > Reviewed-by: Minchan Kim <minchan.kim@xxxxxxxxx> > Acked-by: Johannes Weiner <jweiner@xxxxxxxxxx> Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> Maybe I need to add memcg_is_congested() ... -- 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>