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:
> > 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 <shaohua.li@xxxxxxxxx>
---
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)
--
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