From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752126Ab3KYXuQ (ORCPT ); Mon, 25 Nov 2013 18:50:16 -0500 Received: from mail.linuxfoundation.org ([140.211.169.12]:57322 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751679Ab3KYXuN (ORCPT ); Mon, 25 Nov 2013 18:50:13 -0500 Date: Mon, 25 Nov 2013 15:50:11 -0800 From: Andrew Morton To: Johannes Weiner Cc: Dave Chinner , Rik van Riel , Jan Kara , Vlastimil Babka , Peter Zijlstra , Tejun Heo , Andi Kleen , Andrea Arcangeli , Greg Thelen , Christoph Hellwig , Hugh Dickins , KOSAKI Motohiro , Mel Gorman , Minchan Kim , Michel Lespinasse , Seth Jennings , Roman Gushchin , Ozgun Erdogan , Metin Doslu , linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [patch 7/9] mm: thrash detection-based file cache sizing Message-Id: <20131125155011.2f1320ab422436b1204bd15e@linux-foundation.org> In-Reply-To: <1385336308-27121-8-git-send-email-hannes@cmpxchg.org> References: <1385336308-27121-1-git-send-email-hannes@cmpxchg.org> <1385336308-27121-8-git-send-email-hannes@cmpxchg.org> X-Mailer: Sylpheed 3.2.0beta5 (GTK+ 2.24.10; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, 24 Nov 2013 18:38:26 -0500 Johannes Weiner wrote: > ... > > + * Access frequency and refault distance > + * > + * A workload is trashing when its pages are frequently used but they > + * are evicted from the inactive list every time before another access > + * would have promoted them to the active list. > + * > + * In cases where the average access distance between thrashing pages > + * is bigger than the size of memory there is nothing that can be > + * done - the thrashing set could never fit into memory under any > + * circumstance. > + * > + * However, the average access distance could be bigger than the > + * inactive list, yet smaller than the size of memory. In this case, > + * the set could fit into memory if it weren't for the currently > + * active pages - which may be used more, hopefully less frequently: > + * > + * +-memory available to cache-+ > + * | | > + * +-inactive------+-active----+ > + * a b | c d e f g h i | J K L M N | > + * +---------------+-----------+ So making the inactive list smaller will worsen this problem? If so, don't we have a conflict with this objective: > Right now we have a fixed ratio (50:50) between inactive and active > list but we already have complaints about working sets exceeding half > of memory being pushed out of the cache by simple streaming in the > background. Ultimately, we want to adjust this ratio and allow for a > much smaller inactive list. ? > + * It is prohibitively expensive to accurately track access frequency > + * of pages. But a reasonable approximation can be made to measure > + * thrashing on the inactive list, after which refaulting pages can be > + * activated optimistically to compete with the existing active pages. > + * > + * Approximating inactive page access frequency - Observations: > + * > + * 1. When a page is accesed for the first time, it is added to the "accessed" > + * head of the inactive list, slides every existing inactive page > + * towards the tail by one slot, and pushes the current tail page > + * out of memory. > + * > > ... >