zero deleted blocks

[Konstantin Belousov]

On Mon, Aug 13, 2012 at 09:01:57AM +0300, Petri Helenius wrote:
> 
> Hi,
> 
> Is it possible to have ZFS or UFS to zero out the deallocated blocks
> to facilitate VM disk compaction?

I think TRIM support in UFS can be extended to zero-out the deleted
blocks, with relatively small amount of work. Basically, in
ufs/ffs/ffs_alloc.c:ffs_blkfree(), a BIO_WRITE of zero buffer shall be
issued instead of BIO_DELETE.

More, it seems that zero_region can be often used as a source of zeroes.
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