linux-ext4 - Re: [PATCH] ext4: fix how i_version is modified and turn it on by default V2

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20120515210815.GE1907@localhost.localdomain>
Date:	Tue, 15 May 2012 17:08:15 -0400
From:	Josef Bacik <josef@...hat.com>
To:	"J. Bruce Fields" <bfields@...ldses.org>
Cc:	Josef Bacik <josef@...hat.com>, Andreas Dilger <adilger@...ger.ca>,
	Boaz Harrosh <bharrosh@...asas.com>,
	linux-ext4@...r.kernel.org, linux-nfs@...r.kernel.org,
	tytso@....edu, jack@...e.cz
Subject: Re: [PATCH] ext4: fix how i_version is modified and turn it on by
 default V2

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
--
To unsubscribe from this list: send the line "unsubscribe linux-ext4" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html