From: NeilBrown Subject: Re: [RFC PATCH 1/2] bdi: Create a flag to indicate that a backing device needs stable page writes Date: Tue, 30 Oct 2012 10:48:37 +1100 Message-ID: <20121030104837.2e4b06fc@notabene.brown> References: <20121026101909.GB19617@blackbox.djwong.org> <20121027013524.GA19591@blackbox.djwong.org> <20121029181358.GG18767@quack.suse.cz> <20121029183051.GJ18767@quack.suse.cz> Mime-Version: 1.0 Content-Type: multipart/signed; micalg=PGP-SHA1; boundary="Sig_/KXAUnllFU/8ig4COcDuGsgc"; protocol="application/pgp-signature" Cc: "Darrick J. Wong" , Theodore Ts'o , linux-ext4 , linux-fsdevel To: Jan Kara Return-path: Received: from cantor2.suse.de ([195.135.220.15]:57199 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758494Ab2J2XsU (ORCPT ); Mon, 29 Oct 2012 19:48:20 -0400 In-Reply-To: <20121029183051.GJ18767@quack.suse.cz> Sender: linux-ext4-owner@vger.kernel.org List-ID: --Sig_/KXAUnllFU/8ig4COcDuGsgc Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: quoted-printable On Mon, 29 Oct 2012 19:30:51 +0100 Jan Kara wrote: > On Mon 29-10-12 19:13:58, Jan Kara wrote: > > On Fri 26-10-12 18:35:24, Darrick J. Wong wrote: > > > This creates BDI_CAP_STABLE_WRITES, which indicates that a device req= uires > > > stable page writes. It also plumbs in a sysfs attribute so that admi= ns can > > > check the device status. > > >=20 > > > Signed-off-by: Darrick J. Wong > > I guess Jens Axboe would be the best target for this > > patch (so that he can merge it). The patch looks OK to me. You can add: > > Reviewed-by: Jan Kara > One more thing popped up in my mind: What about NFS, Ceph or md RAID5? > These could (at least theoretically) care about stable writes as well. I'm > not sure if they really started to use them but it would be good to at > least let them know. >=20 What exactly are the semantics of BDI_CAP_STABLE_WRITES ? If I set it for md/RAID5, do I get a cast-iron guarantee that no byte in any page submitted for write will ever change until after I call bio_endio()? If so, is this true for all filesystems? - I would expect a bigger patch wo= uld be needed for that. If not, what exactly are the semantics? Thanks, NeilBrown --Sig_/KXAUnllFU/8ig4COcDuGsgc Content-Type: application/pgp-signature; name=signature.asc Content-Disposition: attachment; filename=signature.asc -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.18 (GNU/Linux) iQIVAwUBUI8V1Tnsnt1WYoG5AQKaUw/+KY6KG7Vb32opbE/7ZSJlE7Yig97VQteR 6zhwHCh713rWt9jUmzL1fgpM6qIzx8fZqcIpegFt6/u8KjydR9qfsvI+LErEHOoe VLMWYN5eYQJhUOctN1HP794Nkg5PJYQbMNH+OurgFaacztJKE51BBwAUP4AT2Lpq F6UF4lLV/CxUTEEVvSqliIWAIjr3bbuHqLFaNo0vhM9Yzshu8WfGMsyLO4rVyVP7 HpYY+IVYipSiLjTAPWx90iNx/PSNtu5XK8VUSBvAmJaE1d43AMTi5wTVrkBYoTMY VAM40Z1Fe/iJ4PyRe8c+D8fUpzYCfxBi0+Tz4wG2HJpYY4InX//jn03AH5kFvm1P fKLrFp8xpg/wX36xJcCX3FKboEzJtBtNmQ6NNkBejUw1s7D0Zkz1NjcTyN2ExIEB aQ+WHixMfsJmsNQ85WZaAegCMN9sWii3W4/6PcaDVSq3M3EbSSAmZgnf5MZNhxsb aBFPfREb93VRGJjf7WhhjgbEi0LRQF2nYkD0kpK7qH+54R5zHz13RcatUF7xewrV bl0RB+9IU8twwX+Km6QCIym1sVu2K5ZPoJV0A0by1uG3wrmyMTmCihjPt+LWt/S4 FXRgzPMh//bicIguwx52+cja2Xj8um5CaeQar0RVrj0UHnRivYa+bx1ItCm6QjlN 327kzCm+7Ek= =WJez -----END PGP SIGNATURE----- --Sig_/KXAUnllFU/8ig4COcDuGsgc--