Path: csiph.com!news.mixmin.net!aioe.org!news.servidellagleba.it!bofh.it!news.nic.it!robomod From: Andrew Morton Newsgroups: linux.kernel Subject: Re: [PATCH 2/3] mm: filemap: only do access activations on reads Date: Mon, 04 Apr 2016 23:30:03 +0200 Message-ID: References: X-Mailer: Sylpheed 3.4.1 (GTK+ 2.24.23; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: robomod@news.nic.it List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Approved: robomod@news.nic.it Lines: 16 Organization: linux.* mail to news gateway X-Original-Cc: Andres Freund , Rik van Riel , linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel-team@fb.com X-Original-Date: Mon, 4 Apr 2016 14:22:33 -0700 X-Original-Message-ID: <20160404142233.cfdea284b8107768fb359efd@linux-foundation.org> X-Original-References: <1459790018-6630-1-git-send-email-hannes@cmpxchg.org> <1459790018-6630-3-git-send-email-hannes@cmpxchg.org> X-Original-Sender: linux-kernel-owner@vger.kernel.org Xref: csiph.com linux.kernel:1370906 On Mon, 4 Apr 2016 13:13:37 -0400 Johannes Weiner wrote: > Andres Freund observed that his database workload is struggling with > the transaction journal creating pressure on frequently read pages. > > Access patterns like transaction journals frequently write the same > pages over and over, but in the majority of cases those pages are > never read back. There are no caching benefits to be had for those > pages, so activating them and having them put pressure on pages that > do benefit from caching is a bad choice. Read-after-write is a pretty common pattern: temporary files for example. What are the opportunities for regressions here? Did you consider providing userspace with a way to hint "this file is probably write-then-not-read"?