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

[Chris Worley <worleys@gmail.com>]

On Mon, May 25, 2009 at 7:14 AM, Goswin von Brederlow <goswin-v-b@web.de> wrote:
> Thomas Glanzmann <thomas@glanzmann.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