From 0e093d99763eb4cea09f8ca4f1d01f34e121d10b Mon Sep 17 00:00:00 2001 From: Mel Gorman Date: Tue, 26 Oct 2010 14:21:45 -0700 Subject: writeback: do not sleep on the congestion queue if there are no congested BDIs or if significant congestion is not being encountered in the current zone If congestion_wait() is called with no BDI congested, the caller will sleep for the full timeout and this may be an unnecessary sleep. This patch adds a wait_iff_congested() that checks congestion and only sleeps if a BDI is congested else, it calls cond_resched() to ensure the caller is not hogging the CPU longer than its quota but otherwise will not sleep. This is aimed at reducing some of the major desktop stalls reported during IO. For example, while kswapd is operating, it calls congestion_wait() but it could just have been reclaiming clean page cache pages with no congestion. Without this patch, it would sleep for a full timeout but after this patch, it'll just call schedule() if it has been on the CPU too long. Similar logic applies to direct reclaimers that are not making enough progress. Signed-off-by: Mel Gorman Cc: Johannes Weiner Cc: Minchan Kim Cc: Wu Fengguang Cc: KAMEZAWA Hiroyuki Cc: KOSAKI Motohiro Cc: Rik van Riel Cc: Jens Axboe Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- include/trace/events/writeback.h | 7 +++++++ 1 file changed, 7 insertions(+) (limited to 'include/trace') diff --git a/include/trace/events/writeback.h b/include/trace/events/writeback.h index d2b2654606ec..89a2b2db4375 100644 --- a/include/trace/events/writeback.h +++ b/include/trace/events/writeback.h @@ -179,6 +179,13 @@ DEFINE_EVENT(writeback_congest_waited_template, writeback_congestion_wait, TP_ARGS(usec_timeout, usec_delayed) ); +DEFINE_EVENT(writeback_congest_waited_template, writeback_wait_iff_congested, + + TP_PROTO(unsigned int usec_timeout, unsigned int usec_delayed), + + TP_ARGS(usec_timeout, usec_delayed) +); + #endif /* _TRACE_WRITEBACK_H */ /* This part must be outside protection */ -- cgit v1.2.3