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 --- mm/page-writeback.c | 3 +++ 1 file changed, 3 insertions(+) --- linux-next.orig/mm/page-writeback.c 2010-12-08 23:54:36.000000000 +0800 +++ linux-next/mm/page-writeback.c 2010-12-08 23:56:55.000000000 +0800 @@ -662,6 +662,9 @@ static void balance_dirty_pages(struct a break; bdi_prev_dirty = bdi_dirty; + if (unlikely(!writeback_in_progress(bdi))) + bdi_start_background_writeback(bdi); + bdi_update_bandwidth(bdi, start_time, bdi_dirty, bdi_thresh); if (bdi_dirty >= task_thresh) { -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/