Re: [PATCH v5.1 0/2] create BLKZEROOUT ioctl that invalidates page cache

[Christoph Hellwig]

On Wed, Mar 02, 2016 at 10:15:02AM +0100, Arnd Bergmann wrote:
> I'm missing the background on this, just saw the patch fly by,
> so sorry if this has been asked before:
> 
> Why do you want to invalidate the cache? Is this to save RAM
> or is something else going to write here and you have to invalidate
> it for correctness?

BLKZEROOUT can be though as a direct I/O operation - it issues a 
WRITE SAME (or similar) command straight to the device to zero
the specified range.  If there was cached data for this range it would
now be stale.