From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: with ECARTIS (v1.0.0; list xfs); Mon, 25 Aug 2008 05:00:41 -0700 (PDT) Received: from cuda.sgi.com ([192.48.176.15]) by oss.sgi.com (8.12.11.20060308/8.12.11/SuSE Linux 0.7) with ESMTP id m7PC0as0010517 for ; Mon, 25 Aug 2008 05:00:37 -0700 Received: from mail2.shareable.org (localhost [127.0.0.1]) by cuda.sgi.com (Spam Firewall) with ESMTP id B24121A4086F for ; Mon, 25 Aug 2008 05:01:59 -0700 (PDT) Received: from mail2.shareable.org (mail2.shareable.org [80.68.89.115]) by cuda.sgi.com with ESMTP id ZFumiwm7MYYbUxtw for ; Mon, 25 Aug 2008 05:01:59 -0700 (PDT) Date: Mon, 25 Aug 2008 13:01:47 +0100 From: Jamie Lokier Subject: Re: XFS vs Elevators (was Re: [PATCH RFC] nilfs2: continuous snapshotting file system) Message-ID: <20080825120146.GC20960@shareable.org> References: <20080821051508.GB5706@disturbed> <200808211933.34565.nickpiggin@yahoo.com.au> <20080821170854.GJ5706@disturbed> <200808221229.11069.nickpiggin@yahoo.com.au> <20080825015922.GP5706@disturbed> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20080825015922.GP5706@disturbed> Sender: xfs-bounce@oss.sgi.com Errors-to: xfs-bounce@oss.sgi.com List-Id: xfs To: Nick Piggin , gus3 , Szabolcs Szakacsits , Andrew Morton , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, xfs@oss.sgi.com Dave Chinner wrote: > To keep on top of this, we keep adding new variations and types and > expect the filesystems to make best use of them (without > documentation) to optimise for certain situations. Example - the > new(ish) BIO_META tag that only CFQ understands. I can change the > way XFS issues bios to use this tag to make CFQ behave the same way > it used to w.r.t. metadata I/O from XFS, but then the deadline and > AS will probably regress because they don't understand that tag and > still need the old optimisations that just got removed. Ditto for > prioritised bio dispatch - CFQ supports it but none of the others > do. There's nothing wrong with adding BIO_META (for example) and other hints in _principle_. You should be able to ignore it with no adverse effects. If its not used by a filesystem (and there's nothing else competing to use the same disk), I would hope to see the same performance as other kernels which don't have it. If the elevators are being changed in such a way that old filesystem code which doesn't use new hint bits is running significantly slower, surely that's blatant elevator regression, and that's where the bugs should be reported and fixed? -- Jamie