linux-ext4 - Re: Ext2/3 block remapping tool

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Message-ID: <20070430122921.GI28367@duck.suse.cz>
Date:	Mon, 30 Apr 2007 14:29:21 +0200
From:	Jan Kara <jack@...e.cz>
To:	Theodore Tso <tytso@....edu>
Cc:	linux-fsdevel@...r.kernel.org, linux-ext4@...r.kernel.org
Subject: Re: Ext2/3 block remapping tool

On Mon 30-04-07 08:09:30, Theodore Tso wrote:
> On Fri, Apr 27, 2007 at 12:09:42PM -0600, Andreas Dilger wrote:
> > I'd prefer that such functionality be integrated with Takashi's online
> > defrag tool, since it needs virtually the same functionality.  For that
> > matter, this is also very similar to the block-mapped -> extents tool
> > from Aneesh.  It doesn't make sense to have so many separate tools for
> > users, especially if they start interfering with each other (i.e. defrag
> > undoes the remapping done by your tool).
> 
> Yep, in fact, I'm really glad that Jan is working on the remapping
> tool because if the on-line defrag kernel interfaces don't have the
> right support for it, then that means we need to fix the on-line
> defrag patches.  :-)
  ;-) Exactly that was the reason why I wrote the userspace program - so
that I have something in hands when we start discussing how the kernel
interface will look like.

> While we're at it, someone want to start thinking about on-line
> shrinking of ext4 filesystems?  Again, the same block remapping
> interfaces for defrag and file access optimizations should also be
> useful for shrinking filesystems (even if some of the files that need
> to be relocated are being actively used).  If not, that probably means
> we got the interface wrong.
  Yes, that's a good idea. Currently it seems to me that block+inode
relocation (we also need for defrag) would be enough to support filesystem
shrinking. Actually, in some ancient times (like 6-7 years ago) I had
written ext2 online filesystem shrinking. Currently, the patch is probably
unusably obsolete but I can still dig it out and look what functions did I
need at that time.

								Honza
-- 
Jan Kara <jack@...e.cz>
SuSE CR Labs
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