linux-ext4 - Re: [RFC] Ext3 online defrag

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Message-Id: <1161721868.29094.35.camel@xenon.msp.redhat.com>
Date:	Tue, 24 Oct 2006 15:31:08 -0500
From:	Russell Cattelan <cattelan@...barn.com>
To:	Theodore Tso <tytso@....edu>
Cc:	David Chinner <dgc@....com>, Jeff Garzik <jeff@...zik.org>,
	Alex Tomas <alex@...sterfs.com>, Jan Kara <jack@...e.cz>,
	linux-fsdevel@...r.kernel.org, linux-ext4@...r.kernel.org
Subject: Re: [RFC] Ext3 online defrag

On Tue, 2006-10-24 at 15:44 -0400, Theodore Tso wrote:
> On Tue, Oct 24, 2006 at 11:59:28PM +1000, David Chinner wrote:
> > That's the wrong way to look at it. if you want the userspace
> > process to specify a location, then you should preallocate it first
> > before doing anything else. There is no need to clutter a simple
> > data mover interface with all sorts of unnecessary error handling.
> 
> This is doable, but it adds a huge amount of complexity before we
> could implement on-line defragmentation.
> 
> First of all, we would need a way of allowing userpsace to specify
> which blocks should be used in the preallocation.
> 
> Secondly, we would need a way of marking blocks as "preallocated but
> not pre-zeroed"; otherwise we would have to zero out all of the blocks
> in order to assure security (don't want userspace programs seeing the
> previous contents of the data blocks), only to do the copy and the
> extents vector swap

Chris Mason page place holder work for DIRECT IO should be applicable to
any pre-allocations?


-- 
Russell Cattelan <cattelan@...barn.com>

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