From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail202.messagelabs.com (mail202.messagelabs.com [216.82.254.227]) by kanga.kvack.org (Postfix) with SMTP id A83276B01EE for ; Wed, 21 Apr 2010 09:19:44 -0400 (EDT) Message-ID: <4BCEFB4C.1070206@redhat.com> Date: Wed, 21 Apr 2010 09:19:08 -0400 From: Rik van Riel MIME-Version: 1.0 Subject: Re: [RFC PATCH 0/3] Avoid the use of congestion_wait under zone pressure References: <20100322235053.GD9590@csn.ul.ie> <4BA940E7.2030308@redhat.com> <20100324145028.GD2024@csn.ul.ie> <4BCC4B0C.8000602@linux.vnet.ibm.com> <20100419214412.GB5336@cmpxchg.org> <4BCD55DA.2020000@linux.vnet.ibm.com> <20100420153202.GC5336@cmpxchg.org> <4BCDE2F0.3010009@redhat.com> <4BCE7DD1.70900@linux.vnet.ibm.com> <4BCEAAC6.7070602@linux.vnet.ibm.com> In-Reply-To: <4BCEAAC6.7070602@linux.vnet.ibm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org To: Christian Ehrhardt Cc: Johannes Weiner , Mel Gorman , Andrew Morton , linux-mm@kvack.org, Nick Piggin , Chris Mason , Jens Axboe , linux-kernel@vger.kernel.org, gregkh@novell.com, Corrado Zoccolo List-ID: On 04/21/2010 03:35 AM, Christian Ehrhardt wrote: > > > Christian Ehrhardt wrote: >> >> >> Rik van Riel wrote: >>> On 04/20/2010 11:32 AM, Johannes Weiner wrote: >>> >>>> The idea is that it pans out on its own. If the workload changes, new >>>> pages get activated and when that set grows too large, we start >>>> shrinking >>>> it again. >>>> >>>> Of course, right now this unscanned set is way too large and we can end >>>> up wasting up to 50% of usable page cache on false active pages. >>> >>> Thing is, changing workloads often change back. >>> >>> Specifically, think of a desktop system that is doing >>> work for the user during the day and gets backed up >>> at night. >>> >>> You do not want the backup to kick the working set >>> out of memory, because when the user returns in the >>> morning the desktop should come back quickly after >>> the screensaver is unlocked. >> >> IMHO it is fine to prevent that nightly backup job from not being >> finished when the user arrives at morning because we didn't give him >> some more cache - and e.g. a 30 sec transition from/to both optimized >> states is fine. >> But eventually I guess the point is that both behaviors are reasonable >> to achieve - depending on the users needs. >> >> What we could do is combine all our thoughts we had so far: >> a) Rik could create an experimental patch that excludes the in flight >> pages >> b) Johannes could create one for his suggestion to "always scan active >> file pages but only deactivate them when the ratio is off and >> otherwise strip buffers of clean pages" I think you are confusing "buffer heads" with "buffers". You can strip buffer heads off pages, but that is not your problem. "buffers" in /proc/meminfo stands for cached metadata, eg. the filesystem journal, inodes, directories, etc... Caching such metadata is legitimate, because it reduces the number of disk seeks down the line. -- 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/ . Don't email: email@kvack.org