On Thu, Jan 26, 2017 at 09:57:45AM +0000, Mel Gorman wrote: > On Mon, Jan 23, 2017 at 01:16:38PM -0500, Johannes Weiner wrote: > > Memory pressure can put dirty pages at the end of the LRU without > > anybody running into dirty limits. Don't start writing individual > > pages from kswapd while the flushers might be asleep. > > > > Signed-off-by: Johannes Weiner <[email protected]> > > I don't understand the motivation for checking the wb_reason name. Maybe > it was easier to eyeball while reading ftraces. The comment about the > flusher not doing its job could also be as simple as the writes took > place and clean pages were reclaimed before dirty_expire was reached. > Not impossible if there was a light writer combined with a heavy reader > or a large number of anonymous faults.
The name change was only because try_to_free_pages() wasn't the only function doing this flusher wakeup anymore. I associate that name with direct reclaim rather than reclaim in general, so I figured this makes more sense. No strong feelings either way, but I doubt this will break anything in userspace. The comment on dirty expiration is a good point. Let's add this to the list of reasons why reclaim might run into dirty data. Fixlet below. > Acked-by: Mel Gorman <[email protected]> Thanks! --- >From 44c4289ab85c0af66cb06de6d1bb72a5c67fd755 Mon Sep 17 00:00:00 2001 From: Johannes Weiner <[email protected]> Date: Thu, 26 Jan 2017 12:41:39 -0500 Subject: [PATCH] mm: vmscan: kick flushers when we encounter dirty pages on the LRU fix Mention dirty expiration as a condition: we need dirty data that is too recent for periodic flushing and not large enough for waking up limit flushing. As per Mel. Signed-off-by: Johannes Weiner <[email protected]> --- mm/vmscan.c | 16 ++++++++-------- 1 file changed, 8 insertions(+), 8 deletions(-) diff --git a/mm/vmscan.c b/mm/vmscan.c index 56ea8d24041f..ccd4bf952cb3 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -1799,15 +1799,14 @@ shrink_inactive_list(unsigned long nr_to_scan, struct lruvec *lruvec, /* * If dirty pages are scanned that are not queued for IO, it * implies that flushers are not doing their job. This can - * happen when memory pressure pushes dirty pages to the end - * of the LRU without the dirty limits being breached. It can - * also happen when the proportion of dirty pages grows not - * through writes but through memory pressure reclaiming all - * the clean cache. And in some cases, the flushers simply - * cannot keep up with the allocation rate. Nudge the flusher - * threads in case they are asleep, but also allow kswapd to - * start writing pages during reclaim. + * happen when memory pressure pushes dirty pages to the end of + * the LRU before the dirty limits are breached and the dirty + * data has expired. It can also happen when the proportion of + * dirty pages grows not through writes but through memory + * pressure reclaiming all the clean cache. And in some cases, + * the flushers simply cannot keep up with the allocation + * rate. Nudge the flusher threads in case they are asleep, but + * also allow kswapd to start writing pages during reclaim. */ if (stat.nr_unqueued_dirty == nr_taken) { wakeup_flusher_threads(0, WB_REASON_VMSCAN); -- 2.11.0
