From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Wed, 23 May 2001 14:02:54 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Wed, 23 May 2001 14:02:44 -0400 Received: from nat-pool-meridian.redhat.com ([199.183.24.200]:60000 "EHLO devserv.devel.redhat.com") by vger.kernel.org with ESMTP id ; Wed, 23 May 2001 14:02:35 -0400 Date: Wed, 23 May 2001 18:34:19 +0100 From: "Stephen C. Tweedie" To: Linus Torvalds Cc: linux-kernel@vger.kernel.org, Stephen Tweedie Subject: Re: DVD blockdevice buffers Message-ID: <20010523183419.I27177@redhat.com> In-Reply-To: <20010518210226.A7147@moserv.hasi> <20010518212531.A6763@suse.de> <9e7ain$lis$1@penguin.transmeta.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.2.5i In-Reply-To: <9e7ain$lis$1@penguin.transmeta.com>; from torvalds@transmeta.com on Sat, May 19, 2001 at 07:36:07PM -0700 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Hi, On Sat, May 19, 2001 at 07:36:07PM -0700, Linus Torvalds wrote: > Right now we don't try to aggressively drop streaming pages, but it's > possible. Using raw devices is a silly work-around that should not be > needed, and this load shows a real problem in current Linux (one soon to > be fixed, I think - Andrea already has some experimental patches for the > page-cache thing). Right. I'd like to see buffered IO able to work well --- apart from the VM issues, it's the easiest way to allow the application to take advantage of readahead. However, there's one sticking point we encountered, which is applications which write to block devices in units smaller than a page. Small block writes get magically transformed into read/modify/write cycles if you shift the block devices into the page cache. Of course, we could just say "then don't do that" and be done with it --- after all, we already have this behaviour when writing to regular files. --Stephen