From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail6.bemta7.messagelabs.com (mail6.bemta7.messagelabs.com [216.82.255.55]) by kanga.kvack.org (Postfix) with ESMTP id 51AFF6B0169 for ; Thu, 28 Jul 2011 20:35:28 -0400 (EDT) Subject: Re: [patch 1/3]vmscan: clear ZONE_CONGESTED for zone with good watermark From: Shaohua Li In-Reply-To: <20110728105611.GJ3010@suse.de> References: <1311840781.15392.407.camel@sli10-conroe> <20110728105611.GJ3010@suse.de> Content-Type: text/plain; charset="UTF-8" Date: Fri, 29 Jul 2011 08:35:25 +0800 Message-ID: <1311899725.15392.416.camel@sli10-conroe> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Mel Gorman Cc: Andrew Morton , linux-mm , Minchan Kim 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 --- 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: email@kvack.org