On Thu, 2011-07-28 at 18:56 +0800, Mel Gorman wrote:

On Thu, Jul 28, 2011 at 04:13:01PM +0800, Shaohua Li wrote:

quoted

correctly clear ZONE_CONGESTED. If a zone watermark is ok, we
should clear ZONE_CONGESTED regardless if this is a high order
allocation, because pages can be reclaimed in other tasks but
ZONE_CONGESTED is only cleared in kswapd.

What problem does this solve?

As it is, for high order allocations it takes the following steps

If reclaiming at high order {
	for each zone {
		if all_unreclaimable
			skip
		if watermark is not met
			order = 0
			loop again
		
		/* watermark is met */
		clear congested
	}
}

If high orders are failing, kswapd balances for order-0 where there
is already a cleaning of ZONE_CONGESTED if the zone was shrunk and
became balanced. I see the case for hunk 1 of the patch because now
it'll clear ZONE_CONGESTED for zones that are already balanced which
might have a noticable effect on wait_iff_congested. Is this what
you see? Even if it is, it does not explain hunk 2 of the patch.

I first looked at the hunk 2 place and thought we don't clear
ZONE_CONGESTED there. I then figured out we need do the same thing for
the hunk 1. But you are correct, with hunk 1, hunk 2 isn't required.
updated patch.



correctly clear ZONE_CONGESTED. If a zone watermark is ok, we
should clear ZONE_CONGESTED because pages can be reclaimed in
other tasks but ZONE_CONGESTED is only cleared in kswapd.

Signed-off-by: Shaohua Li <redacted>
---
 mm/vmscan.c |    3 +++
 1 file changed, 3 insertions(+)

Index: linux/mm/vmscan.c
===================================================================

--- linux.orig/mm/vmscan.c	2011-07-29 08:24:10.000000000 +0800
+++ linux/mm/vmscan.c	2011-07-29 08:26:29.000000000 +0800

@@ -2494,6 +2494,9 @@ loop_again:
 					high_wmark_pages(zone), 0, 0)) {
 				end_zone = i;
 				break;
+			} else {
+				/* If balanced, clear the congested flag */
+				zone_clear_flag(zone, ZONE_CONGESTED);
 			}
 		}
 		if (i < 0)


--

To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>