Return-Path: linux-nfs-owner@vger.kernel.org Received: from fieldses.org ([174.143.236.118]:38941 "EHLO fieldses.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S966022Ab2EOVAv (ORCPT ); Tue, 15 May 2012 17:00:51 -0400 Date: Tue, 15 May 2012 17:00:29 -0400 From: "J. Bruce Fields" To: Josef Bacik Cc: Andreas Dilger , Boaz Harrosh , linux-ext4@vger.kernel.org, linux-nfs@vger.kernel.org, tytso@mit.edu, jack@suse.cz Subject: Re: [PATCH] ext4: fix how i_version is modified and turn it on by default V2 Message-ID: <20120515210029.GA11932@fieldses.org> References: <1337092396-3272-1-git-send-email-josef@redhat.com> <20120515175308.GB1907@localhost.localdomain> <4FB29DAC.3020801@panasas.com> <20120515182914.GC1907@localhost.localdomain> <20120515200533.GD1907@localhost.localdomain> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <20120515200533.GD1907@localhost.localdomain> Sender: linux-nfs-owner@vger.kernel.org List-ID: On Tue, May 15, 2012 at 04:05:34PM -0400, Josef Bacik wrote: > On Tue, May 15, 2012 at 01:55:33PM -0600, Andreas Dilger wrote: > > It should be fairly straight forward to have a flag set in the ext4 > > superblock (s_state flag?) that indicates that the filesystem has > > been exported via NFS. There might be other optimizations that can > > be done based on this (e.g. avoid some of the directory cookie > > hijinx that are only needed if NFS has exported the filesystem and > > needs to keep persistent cookies across reboots). > > > > I think that the ext4_mark_inode_dirty() performance problem could > > be at least partially fixed by deferring the copy of in-core inode > > to on-disk inode to use a journal commit callback. This is far more > > work than just setting a flag in the superblock, but it has the > > potential to _improve_ performance rather than make it worse. Could you give any more pointers for an ext4 ignoramus? (Where *is* the journal commit code that would need the callback? And where is the copy currently done?) > Yeah Btrfs doesn't have this sort of problem since we delay inode > updating sinc it is so costly, we simply let it hang around in the > in-core inode until we feel like updating it at some point down the > road. I'll put together a feature flag or something to make it be > enabled for always if somebody turns it on. Thanks for looking at this. A feature flag would be an improvement over a mount option. If the flag makes a noticeable difference to performance, then it makes me nervous toggling it automatically. And what will we do if statx starts returning i_version to userspace? --b.