linux-ext4 - Re: zero out blocks of freed user data for operation a virtual machine environment

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Message-ID: <20090525120320.GA25908@mit.edu>
Date:	Mon, 25 May 2009 08:03:20 -0400
From:	Theodore Tso <tytso@....edu>
To:	Thomas Glanzmann <thomas@...nzmann.de>,
	Arjan van de Ven <arjan@...radead.org>, tytso@...nk.org,
	LKML <linux-kernel@...r.kernel.org>, linux-ext4@...r.kernel.org
Subject: Re: zero out blocks of freed user data for operation a virtual
	machine environment

On Sun, May 24, 2009 at 07:39:33PM +0200, Thomas Glanzmann wrote:
> Hello,
> 
> > > tunable feature that zeroes our free data
> 
> > wouldn't it be better if the VM's would just support the TRIM command?
> 
> the resources available to me indicate that the TRIM command is a not
> yet standarized command targeted at SSD disks to indicate free disk
> space. Does ext3/4 trigger a block device layer call that could result
> in a TRIM command?

Yes, it does, sb_issue_discard().  So if you wanted to hook into this
routine with a function which issued calls to zero out blocks, it
would be easy to create a private patch.

					- Ted
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