From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id DA227C6FA8A for ; Thu, 8 Sep 2022 23:45:32 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230204AbiIHXpb (ORCPT ); Thu, 8 Sep 2022 19:45:31 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:34434 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229919AbiIHXpZ (ORCPT ); Thu, 8 Sep 2022 19:45:25 -0400 Received: from smtp-out1.suse.de (smtp-out1.suse.de [195.135.220.28]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id AE9C8A2607; Thu, 8 Sep 2022 16:45:24 -0700 (PDT) Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by smtp-out1.suse.de (Postfix) with ESMTPS id F2FDB336AE; Thu, 8 Sep 2022 23:45:22 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_rsa; t=1662680723; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=x71AWVjMQBSYFLOAJJTAszIVLpOBTb+pkZdb7Q/uDY4=; b=yFmHsA2rRxVQg6WEGxwoVfPC0V5zZkZDY4cx1KPO/TmJhR/ffEo/wSjt67etkyuC8Q8XCN j2sb2WtBnwcC2Fza6vmBQmFoou8DP1uK0yAu8uIki87ZTitT7S+Ahb8aG21hdcWcH/EQay p4elSw0vOTGCeXaU4Okdl7R+VOvMxY4= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_ed25519; t=1662680723; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=x71AWVjMQBSYFLOAJJTAszIVLpOBTb+pkZdb7Q/uDY4=; b=HjT5yEfaqGECKpGJ+uLMTy96VmaZa3x6X6Nsrlljor4fRUr4fgAcW1Lcg9WfVmJDQvq2Yv 3QPoT1gLKqeetTDw== Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by imap2.suse-dmz.suse.de (Postfix) with ESMTPS id CCEF413A6D; Thu, 8 Sep 2022 23:45:14 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap2.suse-dmz.suse.de with ESMTPSA id naC6H4p+GmNHHgAAMHmgww (envelope-from ); Thu, 08 Sep 2022 23:45:14 +0000 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 From: "NeilBrown" To: "Jeff Layton" Cc: "J. Bruce Fields" , "Theodore Ts'o" , "Jan Kara" , adilger.kernel@dilger.ca, djwong@kernel.org, david@fromorbit.com, trondmy@hammerspace.com, viro@zeniv.linux.org.uk, zohar@linux.ibm.com, xiubli@redhat.com, chuck.lever@oracle.com, lczerner@redhat.com, brauner@kernel.org, fweimer@redhat.com, linux-man@vger.kernel.org, linux-api@vger.kernel.org, linux-btrfs@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, ceph-devel@vger.kernel.org, linux-ext4@vger.kernel.org, linux-nfs@vger.kernel.org, linux-xfs@vger.kernel.org Subject: Re: [man-pages RFC PATCH v4] statx, inode: document the new STATX_INO_VERSION field In-reply-to: <53298467f5fce443c70ef6821e055d10caf9331e.camel@kernel.org> References: <79aaf122743a295ddab9525d9847ac767a3942aa.camel@kernel.org>, <20220907125211.GB17729@fieldses.org>, <771650a814ab1ff4dc5473d679936b747d9b6cf5.camel@kernel.org>, <20220907135153.qvgibskeuz427abw@quack3>, <166259786233.30452.5417306132987966849@noble.neil.brown.name>, <20220908083326.3xsanzk7hy3ff4qs@quack3>, , <02928a8c5718590bea5739b13d6b6ebe66cac577.camel@kernel.org>, <20220908155605.GD8951@fieldses.org>, <9e06c506fd6b3e3118da0ec24276e85ea3ee45a1.camel@kernel.org>, <20220908182252.GA18939@fieldses.org>, <44efe219dbf511492b21a653905448d43d0f3363.camel@kernel.org>, <166267807678.30452.18035749642786839300@noble.neil.brown.name>, <53298467f5fce443c70ef6821e055d10caf9331e.camel@kernel.org> Date: Fri, 09 Sep 2022 09:45:09 +1000 Message-id: <166268070965.30452.8884091101479997991@noble.neil.brown.name> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 09 Sep 2022, Jeff Layton wrote: > On Fri, 2022-09-09 at 09:01 +1000, NeilBrown wrote: > > On Fri, 09 Sep 2022, Jeff Layton wrote: > > > On Thu, 2022-09-08 at 14:22 -0400, J. Bruce Fields wrote: > > > > On Thu, Sep 08, 2022 at 01:40:11PM -0400, Jeff Layton wrote: > > > > > Yeah, ok. That does make some sense. So we would mix this into the > > > > > i_version instead of the ctime when it was available. Preferably, w= e'd > > > > > mix that in when we store the i_version rather than adding it after= ward. > > > > >=20 > > > > > Ted, how would we access this? Maybe we could just add a new (gener= ic) > > > > > super_block field for this that ext4 (and other filesystems) could > > > > > populate at mount time? > > > >=20 > > > > Couldn't the filesystem just return an ino_version that already inclu= des > > > > it? > > > >=20 > > >=20 > > > Yes. That's simple if we want to just fold it in during getattr. If we > > > want to fold that into the values stored on disk, then I'm a little less > > > clear on how that will work. > > >=20 > > > Maybe I need a concrete example of how that will work: > > >=20 > > > Suppose we have an i_version value X with the previous crash counter > > > already factored in that makes it to disk. We hand out a newer version > > > X+1 to a client, but that value never makes it to disk. > >=20 > > As I understand it, the crash counter would NEVER appear in the on-disk > > i_version. > > The crash counter is stable while a filesystem is mounted so is the same > > when loading an inode from disk and when writing it back. > >=20 > > When loading, add crash counter to on-disk i_version to provide > > in-memory i_version. > > when storing, subtract crash counter from in-memory i_version to provide > > on-disk i_version. > >=20 > > "add" and "subtract" could be any reversible hash, and its inverse. I > > would probably shift the crash counter up 16 and add/subtract. > >=20 > >=20 >=20 > If you store the value with the crash counter already factored-in, then > not every inode would end up being invalidated after a crash. If we try > to mix it in later, the client will end up invalidating the cache even > for inodes that had no changes. How do we know which inodes need the crash counter merged in? I thought the whole point of the crash counter was that it affected every file (easy, safe, expensive, but hopefully rare enough that the expense could be justified). NeilBrown >=20 > > >=20 > > > The machine crashes and comes back up, and we get a query for i_version > > > and it comes back as X. Fine, it's an old version. Now there is a write. > > > What do we do to ensure that the new value doesn't collide with X+1?=20 > > > --=20 > > > Jeff Layton > > >=20 >=20 > --=20 > Jeff Layton >=20