On Thu, Dec 02, 2010 at 07:03:33AM +0800, Andrew Morton wrote: > On Wed, 1 Dec 2010 21:38:18 +0800 > Wu Fengguang <fengguang.wu@xxxxxxxxx> wrote: > > > It shows that > > > > 1) io_schedule_timeout(200ms) always return immediately for iostat, > > forming a busy loop. How can this happen? When iostat received > > some signal? Then we may have to break out of the loop on catching > > signals. Note that I already have > > if (fatal_signal_pending(current)) > > break; > > in the balance_dirty_pages() loop. Obviously that's not enough. > > Presumably the calling task has singal_pending(). > > Using TASK_INTERRUPTIBLE in balance_dirty_pages() seems wrong. If it's > going to do that then it must break out if signal_pending(), otherwise > it's pretty much guaranteed to degenerate into a busywait loop. Right. It seems not rewarding enough to check signal_pending(). We've already been able to response to signals much faster than before (which takes more time to block in get_request_wait()). > Plus we *do* want these processes to appear in D state and to > contribute to load average. > > So it should be TASK_UNINTERRUPTIBLE. Fair enough. I do missed the D state (without the long wait :). Here is the patch. Thanks, Fengguang --- Subject: writeback: do uninterruptible sleep in balance_dirty_pages() Date: Thu Dec 02 09:31:19 CST 2010 Using TASK_INTERRUPTIBLE in balance_dirty_pages() seems wrong. If it's going to do that then it must break out if signal_pending(), otherwise it's pretty much guaranteed to degenerate into a busywait loop. Plus we *do* want these processes to appear in D state and to contribute to load average. So it should be TASK_UNINTERRUPTIBLE. -- Andrew Morton Signed-off-by: Wu Fengguang <fengguang.wu@xxxxxxxxx> --- mm/page-writeback.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- linux-next.orig/mm/page-writeback.c 2010-12-02 09:30:29.000000000 +0800 +++ linux-next/mm/page-writeback.c 2010-12-02 09:30:34.000000000 +0800 @@ -636,7 +636,7 @@ pause: pages_dirtied, pause); bdi_update_write_bandwidth(bdi, &bw_time, &bw_written); - __set_current_state(TASK_INTERRUPTIBLE); + __set_current_state(TASK_UNINTERRUPTIBLE); io_schedule_timeout(pause); bdi_update_write_bandwidth(bdi, &bw_time, &bw_written); -- 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>