From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail144.messagelabs.com (mail144.messagelabs.com [216.82.254.51]) by kanga.kvack.org (Postfix) with SMTP id 85DD46B004F for ; Fri, 1 May 2009 10:06:06 -0400 (EDT) Message-ID: <49FB01C1.6050204@redhat.com> Date: Fri, 01 May 2009 10:05:53 -0400 From: Rik van Riel MIME-Version: 1.0 Subject: Re: [PATCH] vmscan: evict use-once pages first (v2) References: <20090428044426.GA5035@eskimo.com> <20090428192907.556f3a34@bree.surriel.com> <1240987349.4512.18.camel@laptop> <20090429114708.66114c03@cuia.bos.redhat.com> <20090430072057.GA4663@eskimo.com> <20090430174536.d0f438dd.akpm@linux-foundation.org> <20090430205936.0f8b29fc@riellaptop.surriel.com> <20090430181340.6f07421d.akpm@linux-foundation.org> <20090430215034.4748e615@riellaptop.surriel.com> <20090430195439.e02edc26.akpm@linux-foundation.org> In-Reply-To: <20090430195439.e02edc26.akpm@linux-foundation.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org To: Andrew Morton Cc: elladan@eskimo.com, peterz@infradead.org, linux-kernel@vger.kernel.org, tytso@mit.edu, kosaki.motohiro@jp.fujitsu.com, linux-mm@kvack.org List-ID: Andrew Morton wrote: >> When we implement working set protection, we might as well >> do it for frequently accessed unmapped pages too. There is >> no reason to restrict this protection to mapped pages. > > Well. Except for empirical observation, which tells us that biasing > reclaim to prefer to retain mapped memory produces a better result. That used to be the case because file-backed and swap-backed pages shared the same set of LRUs, while each following a different page reclaim heuristic! Today: 1) file-backed and swap-backed pages are separated, 2) the majority of mapped pages are on the swap-backed LRUs 3) the accessed bit on active pages no longer means much, for good scalability reasons, and 4) because of (3), we cannot really provide special treatment to any individual page any more, however This means we need to provide our working set protection on a per-list basis, by tweaking the scan rate or avoiding scanning of the active file list alltogether under certain conditions. As a side effect, this will help protect frequently accessed file pages (good for ftp and nfs servers), indirect blocks, inode buffers and other frequently used metadata. -- All rights reversed. -- 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