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.
--
Mel Gorman
SUSE Labs
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