Return-Path: linux-nfs-owner@vger.kernel.org Received: from mx1.redhat.com ([209.132.183.28]:43681 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S966836Ab2EOVIs (ORCPT ); Tue, 15 May 2012 17:08:48 -0400 Date: Tue, 15 May 2012 17:08:15 -0400 From: Josef Bacik To: "J. Bruce Fields" Cc: Josef Bacik , 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: <20120515210815.GE1907@localhost.localdomain> 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> <20120515210029.GA11932@fieldses.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <20120515210029.GA11932@fieldses.org> Sender: linux-nfs-owner@vger.kernel.org List-ID: On Tue, May 15, 2012 at 05:00:29PM -0400, J. Bruce Fields wrote: > 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?) > The copy is currently done in mark_inode_dirty(), I'm looking into what would need to be done to get the inodes to update the on disk stuff on journal commit only, but I worry that will make commits take way longer than normal and cause other issues. > > 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? > Well statx can return flags right? I'm sure we could just have a flag that says "hey iversion is completely useless." Thanks, Josef