From mboxrd@z Thu Jan 1 00:00:00 1970 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 15:48:44 +1100 Message-ID: <20121030154844.1898f068@notabene.brown> References: <20121026101909.GB19617@blackbox.djwong.org> <20121027013524.GA19591@blackbox.djwong.org> Mime-Version: 1.0 Content-Type: multipart/signed; micalg=PGP-SHA1; boundary="Sig_/c/itFBuq+A.7zMntXTa.IYL"; protocol="application/pgp-signature" Cc: "Darrick J. Wong" , "Theodore Ts'o" , linux-ext4 , linux-fsdevel To: "Martin K. Petersen" Return-path: Received: from cantor2.suse.de ([195.135.220.15]:36379 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752527Ab2J3Es0 (ORCPT ); Tue, 30 Oct 2012 00:48:26 -0400 In-Reply-To: Sender: linux-fsdevel-owner@vger.kernel.org List-ID: --Sig_/c/itFBuq+A.7zMntXTa.IYL Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: quoted-printable On Tue, 30 Oct 2012 00:10:22 -0400 "Martin K. Petersen" wrote: > >>>>> "Darrick" =3D=3D Darrick J Wong writes: >=20 > Darrick> This creates BDI_CAP_STABLE_WRITES, which indicates that a > Darrick> device requires stable page writes. It also plumbs in a sysfs > Darrick> attribute so that admins can check the device status. >=20 > Might be nice to make the sysfs knob tweakable. Also, don't forget to > add a suitable blurb to Documentation/ABI/. It isn't at all clear to me that having the sysfs knob 'tweakable' is a go= od idea. From the md/raid5 perspective, I would want to know for certain whether the pages in a give bio are guaranteed not to change, or if they might. I could set the BDI_CAP_STABLE_WRITES and believe they will never change, = or test the BDI_CAP_STABLE_WRITES and let that tell me if they might change or not. But if the bit can be changed at any moment, then it can never be trusted and so becomes worthless to me. At the very least it should only be possible to change it when there is no IO in flight. NeilBrown >=20 > Feel free to add my Acked-by: >=20 --Sig_/c/itFBuq+A.7zMntXTa.IYL Content-Type: application/pgp-signature; name=signature.asc Content-Disposition: attachment; filename=signature.asc -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.18 (GNU/Linux) iQIVAwUBUI9cLDnsnt1WYoG5AQLmLA//U5Xz60zeREjktAv1PIv/31S/KdEceRXt ipilRltZGso/AntT4gyNfAU8wzojTKJxcVY8nmE+e0M2HsAks5y2WsdiqK9Sfkg8 S6tsxqJpEPMYJVg6uPIMAZvM5OjQWBtSMHDaWt/mWhzQq9eF9EV0dJNmEXZLEqMA zQO+nu3tnK4VEkwCtXFb+z4wJkidDtUT+Zsl+a920COORJBGAkNX/M2BhQDodaRG Hfx9StPbgWgWPGl98t/LbQN8eu2/eqyij0oNtWVN6D6FSbnemphsusDjwyIftXuY RTzSbMijTyojNfhZT73rVkduHa6evAlQ5jhZPN+G/9mHdN9J2cAm0zDt8/BnRzjO Hu6W9mqe2XZNEghVPZjqjAWl+UBBUXU2GfJHxkZyEz3jv1WZKLDfsdigyeVxYd2K YYd7pM3TUQmniUDvqHSiynGFwWWI+MRpg/96Fr5IxxJjdBW1Wyn9kqD7G/1uTTlw kze1d3W2zAg4aRoNs9PSWaGvaEcXkIrJjnHpM6mi0TTA0vFfr/Fa04O1axjTQv4+ KQBASb2TlQC0iN3W8NLc97yyTpurJMZJ2CQDAwL+k0nKxy+wqXcoeASKs3OCXkCR EVIFMpQkYvAIAB5rIsMrdpPkJvW9iQuQNC02e8pKavZBZyKmWZVmqz+XqybhCvGf 8OP8NUs4lJ0= =hcZ+ -----END PGP SIGNATURE----- --Sig_/c/itFBuq+A.7zMntXTa.IYL--