Re: [Qemu-devel] [RFC PATCH] block: optimize zero writes with bdrv_write_zeroes

[Fam Zheng <famz@redhat.com>]

On Sat, 02/22 14:00, Peter Lieven wrote:
> this patch tries to optimize zero write requests
> by automatically using bdrv_write_zeroes if it is
> supported by the format.
> 
> i know that there is a lot of potential for discussion, but i would
> like to know what the others think.
> 
> this should significantly speed up file system initialization and
> should speed zero write test used to test backend storage performance.
> 
> the difference can simply be tested by e.g.
> 
> dd if=/dev/zero of=/dev/vdX bs=1M
> 
> Signed-off-by: Peter Lieven <pl@kamp.de>
> ---

With this patch, is is still possible to actually do zero fill? Prefill is
usually writing zeroes too, but according to the semantic, bdrv_write_zeroes
may just set L2 entry flag without allocating clusters, which won't satisfy
that.

Thanks,
Fam