From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail203.messagelabs.com (mail203.messagelabs.com [216.82.254.243]) by kanga.kvack.org (Postfix) with SMTP id 9C5C3900137 for ; Sun, 31 Jul 2011 20:43:33 -0400 (EDT) Subject: Re: [PATCH] kswapd: avoid unnecessary rebalance after an unsuccessful balancing From: "Alex,Shi" In-Reply-To: <20110729154031.GV3010@suse.de> References: <1311952990-3844-1-git-send-email-alex.shi@intel.com> <20110729154031.GV3010@suse.de> Content-Type: text/plain; charset="UTF-8" Date: Mon, 01 Aug 2011 08:45:17 +0800 Message-ID: <1312159517.27358.2446.camel@debian> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Mel Gorman Cc: "linux-mm@kvack.org" , "P@draigBrady.com" , "linux-kernel@vger.kernel.org" , "andrea@cpushare.com" , "Chen, Tim C" , "Li, Shaohua" , "akpm@linux-foundation.org" , "riel@redhat.com" , "luto@mit.edu" On Fri, 2011-07-29 at 23:40 +0800, Mel Gorman wrote: > On Fri, Jul 29, 2011 at 11:23:10PM +0800, Alex Shi wrote: > > In commit 215ddd66, Mel Gorman said kswapd is better to sleep after a > > unsuccessful balancing if there is tighter reclaim request pending in > > the balancing. In this scenario, the 'order' and 'classzone_idx' > > that are checked for tighter request judgment is incorrect, since they > > aren't the one kswapd should read from new pgdat, but the last time pgdat > > value for just now balancing. Then kswapd will skip try_to_sleep func > > and rebalance the last pgdat request. It's not our expected behavior. > > > > So, I added new variables to distinguish the returned order/classzone_idx > > from last balancing, that can resolved above issue in that scenario. > > > > I'm afraid this changelog is very difficult to read and I do not see > what problem you are trying to solve and I do not see what this patch > might solve. > > When balance_pgdat() returns with a lower classzone or order, the values > stored in pgdat are not re-read and instead it tries to go to sleep > based on the starting request. Something like; Thanks for your comments, I will use this comments style next time, list request A, B etc. > > 1. Read pgdat request A (classzone_idx, order) Assume the order of A > 0, like is 3. > 2. balance_pgdat() > 3. During pgdat, a new pgdat request B (classzone_idx, order) is placed > 4. balance_pgdat() returns but failed so classzone_idx is lower Another balance_pgdat() failure indicate is returned order == 0, am I right? If so, the next step of kswapd is not trying to sleep, but do request A balance again. And I thought this behavior doesn't match the comments in kswapd. > 5. Try to sleep based on pgdat request A > > i.e. pgdat request B is not read and there is a comment explaining > why pgdat request B is not read after balance_pgdat() fails. > > This patch adds some variables that might improve the readability > for some people but otherwise I can't see what problem is being > fixed. What did I miss? > -- 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