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 A23DF6B0169 for ; Mon, 8 Aug 2011 08:51:46 -0400 (EDT) Message-ID: <4E3FDBD7.2030801@parallels.com> Date: Mon, 8 Aug 2011 16:51:35 +0400 From: Konstantin Khlebnikov MIME-Version: 1.0 Subject: Re: [PATCH 1/2] vmscan: promote shared file mapped pages References: <20110808110658.31053.55013.stgit@localhost6> <4E3FD403.6000400@parallels.com> In-Reply-To: Content-Type: text/plain; charset="ISO-8859-1"; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Pekka Enberg Cc: "linux-mm@kvack.org" , Andrew Morton , "linux-kernel@vger.kernel.org" , Wu Fengguang , KAMEZAWA Hiroyuki , Johannes Weiner Pekka Enberg wrote: > On Mon, Aug 8, 2011 at 3:18 PM, Konstantin Khlebnikov > wrote: >> Pekka Enberg wrote: >>> >>> Hi Konstantin, >>> >>> On Mon, Aug 8, 2011 at 2:06 PM, Konstantin Khlebnikov >>> wrote: >>>> >>>> Commit v2.6.33-5448-g6457474 (vmscan: detect mapped file pages used only >>>> once) >>>> greatly decreases lifetime of single-used mapped file pages. >>>> Unfortunately it also decreases life time of all shared mapped file >>>> pages. >>>> Because after commit v2.6.28-6130-gbf3f3bc (mm: don't mark_page_accessed >>>> in fault path) >>>> page-fault handler does not mark page active or even referenced. >>>> >>>> Thus page_check_references() activates file page only if it was used >>>> twice while >>>> it stays in inactive list, meanwhile it activates anon pages after first >>>> access. >>>> Inactive list can be small enough, this way reclaimer can accidentally >>>> throw away any widely used page if it wasn't used twice in short period. >>>> >>>> After this patch page_check_references() also activate file mapped page >>>> at first >>>> inactive list scan if this page is already used multiple times via >>>> several ptes. >>>> >>>> Signed-off-by: Konstantin Khlebnikov >>> >>> Both patches seem reasonable but the changelogs don't really explain >>> why you're doing the changes. How did you find out about the problem? >>> Is there some workload that's affected? How did you test your changes? >>> >> >> I found this while trying to fix degragation in rhel6 (~2.6.32) from rhel5 >> (~2.6.18). >> There a complete mess with>100 web/mail/spam/ftp containers, >> they share all their files but there a lot of anonymous pages: >> ~500mb shared file mapped memory and 15-20Gb non-shared anonymous memory. >> In this situation major-pagefaults are very costly, because all containers >> share the same page. >> In my load kernel created a disproportionate pressure on the file memory, >> compared with the anonymous, >> they equaled only if I raise swappiness up to 150 =) >> >> These patches actually wasn't helped a lot in my problem, >> but I saw noticable (10-20 times) reduce in count and average time of >> major-pagefault in file-mapped areas. >> >> Actually both patches are fixes for commit v2.6.33-5448-g6457474, >> because it was aimed at one scenario (singly used pages), >> but it breaks the logic in other scenarios (shared and/or executable pages) > > It'd be nice to have such details in the changelogs. FWIW, It's not quite honest, I did not do any measurements in the mainline kernel, I only boot 3.1-rc1 with them on my laptop. It would be nice to repeat the measurements from v2.6.30-5507-g8cab475, but I do not have time for that right now. > > Acked-by: Pekka Enberg -- 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