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

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Message-ID: <f3177b9e0905251026u54d6b1e0s884dbdedf74b17cd@mail.gmail.com>
Date:	Mon, 25 May 2009 11:26:15 -0600
From:	Chris Worley <worleys@...il.com>
To:	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 Mon, May 25, 2009 at 7:14 AM, Goswin von Brederlow <goswin-v-b@....de> wrote:
> Thomas Glanzmann <thomas@...nzmann.de> writes:
> > Hello Ted,
> >
> >> 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.
> >
> > that sounds good because it wouldn't only target the most used
> > filesystem but every other filesystem that uses the interface as well.
> > Do you think that a tunable or configurable patch has a chance to hit
> > upstream as well?
> >
> >         Thomas
>
> I could imagine a device mapper target that eats TRIM commands and
> writes out zeroes instead. That should be easy to maintain outside or
> inside the upstream kernel source.

Why bother with a time-consuming performance-draining operation?
There are devices that already support TRIM/discard commands today,
and once you discard a block, it's completely irretrievable (you'll
just get back zeros if you try to read that block w/o writing it after
the discard).

Chris
>
>
> MfG
>        Goswin
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