Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757303AbZJ1DyF (ORCPT ); Tue, 27 Oct 2009 23:54:05 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1757291AbZJ1DyE (ORCPT ); Tue, 27 Oct 2009 23:54:04 -0400 Received: from fgwmail7.fujitsu.co.jp ([192.51.44.37]:34593 "EHLO fgwmail7.fujitsu.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757258AbZJ1DyD (ORCPT ); Tue, 27 Oct 2009 23:54:03 -0400 X-SecurityPolicyCheck-FJ: OK by FujitsuOutboundMailChecker v1.3.1 From: KOSAKI Motohiro To: Andrew Morton Subject: Re: [PATCH 3/3] vmscan: Force kswapd to take notice faster when high-order watermarks are being hit Cc: kosaki.motohiro@jp.fujitsu.com, Mel Gorman , stable@kernel.org, linux-kernel@vger.kernel.org, "linux-mm@kvack.org\"" , Frans Pop , Jiri Kosina , Sven Geggus , Karol Lewandowski , Tobias Oetiker , Pekka Enberg , Rik van Riel , Christoph Lameter , Stephan von Krawczynski , Kernel Testers List In-Reply-To: <20091027131905.410ec04a.akpm@linux-foundation.org> References: <1256650833-15516-4-git-send-email-mel@csn.ul.ie> <20091027131905.410ec04a.akpm@linux-foundation.org> Message-Id: <20091028115505.FD88.A69D9226@jp.fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit X-Mailer: Becky! ver. 2.50.07 [ja] Date: Wed, 28 Oct 2009 12:54:04 +0900 (JST) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2879 Lines: 91 > On Tue, 27 Oct 2009 13:40:33 +0000 > Mel Gorman wrote: > > > When a high-order allocation fails, kswapd is kicked so that it reclaims > > at a higher-order to avoid direct reclaimers stall and to help GFP_ATOMIC > > allocations. Something has changed in recent kernels that affect the timing > > where high-order GFP_ATOMIC allocations are now failing with more frequency, > > particularly under pressure. This patch forces kswapd to notice sooner that > > high-order allocations are occuring. > > "something has changed"? Shouldn't we find out what that is? if kswapd_max_order was changed, kswapd quickly change its own reclaim order. old: 1. happen order-0 allocation 2. kick kswapd 3. happen high-order allocation 4. change kswapd_max_order, but kswapd continue order-0 reclaim. 5. kswapd end order-0 reclaim and exit balance_pgdat 6. kswapd() restart balance_pdgat() with high-order new: 1. happen order-0 allocation 2. kick kswapd 3. happen high-order allocation 4. change kswapd_max_order 5. kswapd notice it and quickly exit balance_pgdat() 6. kswapd() restart balance_pdgat() with high-order > > > --- > > mm/vmscan.c | 9 +++++++++ > > 1 files changed, 9 insertions(+), 0 deletions(-) > > > > diff --git a/mm/vmscan.c b/mm/vmscan.c > > index 64e4388..7eceb02 100644 > > --- a/mm/vmscan.c > > +++ b/mm/vmscan.c > > @@ -2016,6 +2016,15 @@ loop_again: > > priority != DEF_PRIORITY) > > continue; > > > > + /* > > + * Exit the function now and have kswapd start over > > + * if it is known that higher orders are required > > + */ > > + if (pgdat->kswapd_max_order > order) { > > + all_zones_ok = 1; > > + goto out; > > + } > > + > > if (!zone_watermark_ok(zone, order, > > high_wmark_pages(zone), end_zone, 0)) > > all_zones_ok = 0; > > So this handles the case where some concurrent thread or interrupt > increases pgdat->kswapd_max_order while kswapd was running > balance_pgdat(), yes? Yes. > Does that actually happen much? Enough for this patch to make any > useful difference? In typical use-case, it doesn't have so much improvement. However some driver use high-order allocation on interrupt context. It mean we need quickly reclaim before GFP_ATOMIC allocation failure. I agree these driver is ill. but... We can't ignore enduser bug report. > > If one where to whack a printk in that `if' block, how often would it > trigger, and under what circumstances? > > > If the -stable maintainers were to ask me "why did you send this" then > right now my answer would have to be "I have no idea". Help. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/