On Mon, Dec 13, 2010 at 10:47:04PM +0800, Wu, Fengguang wrote: > It's possible for some one to suddenly eat lots of memory, > leading to sudden drop of global dirty limit. So a dirtier > task may get hard throttled immediately without some previous > balance_dirty_pages() call to invoke background writeback. > > In this case we need to check for background writeback earlier in the > loop to avoid stucking the application for very long time. This was not > a problem before the IO-less balance_dirty_pages() because it will try > to write something and then break out of the loop regardless of the > global limit. > > Another scheme this check will help is, the dirty limit is too close to > the background threshold, so that someone manages to jump directly into > the pause threshold (background+dirty)/2. > > Signed-off-by: Wu Fengguang <fengguang.wu@xxxxxxxxx> > --- > mm/page-writeback.c | 3 +++ > 1 file changed, 3 insertions(+) > > --- linux-next.orig/mm/page-writeback.c 2010-12-13 21:46:16.000000000 +0800 > +++ linux-next/mm/page-writeback.c 2010-12-13 21:46:17.000000000 +0800 > @@ -748,6 +748,9 @@ static void balance_dirty_pages(struct a > bdi_stat(bdi, BDI_WRITEBACK); > } > > + if (unlikely(!writeback_in_progress(bdi))) > + bdi_start_background_writeback(bdi); > + > bdi_update_bandwidth(bdi, start_time, bdi_dirty, bdi_thresh); > > /* > The above patch allows this simplification. --- Subject: writeback: start background writeback earlier - handle laptop mode Date: Wed Dec 15 20:15:54 CST 2010 The laptop mode handling can be simplified since we've kick background writeback inside the balance_dirty_pages() loop on dirty_exceeded. Signed-off-by: Wu Fengguang <fengguang.wu@xxxxxxxxx> --- mm/page-writeback.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) --- linux-next.orig/mm/page-writeback.c 2010-12-15 20:14:33.000000000 +0800 +++ linux-next/mm/page-writeback.c 2010-12-15 20:15:39.000000000 +0800 @@ -891,8 +891,10 @@ pause: * In normal mode, we start background writeout at the lower * background_thresh, to keep the amount of dirty memory low. */ - if ((laptop_mode && dirty_exceeded) || - (!laptop_mode && (nr_reclaimable > background_thresh))) + if (laptop_mode) + return; + + if (nr_reclaimable > background_thresh) bdi_start_background_writeback(bdi); } -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom policy in Canada: sign http://dissolvethecrtc.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>