Re: [Qemu-devel] [PATCH 1/1] nbd: increase maximum size of the PWRITE_ZERO request

[Eric Blake]

On 02/08/2018 07:23 AM, Edgar Kaziakhmedov wrote:
> Upstream NBD protocol implementation supports an efficient zero out
> mechanism over the wire, along with the ability to check whether a
> client allows using a hole.
>
> Accordingly, since PWRITE_ZERO doesn't involve any payload on the wire,
> increase a maximum size of the PWRITE_ZERO request up to 1Gb (aligned).
> Moreover, such change will decrease the number of PWRITE_ZERO NBD commands
> in comparison with the current 32M limit. The benefits of
> the larger constraint can be examined in a block mirroring over NBD.
>
> Signed-off-by: Edgar Kaziakhmedov <address@hidden>
> ---
>   block/nbd.c         | 2 +-
>   include/block/nbd.h | 3 +++
>   2 files changed, 4 insertions(+), 1 deletion(-)

I've posted a counter-proposal series that should accomplish the same 
effect, but in a way (soon to be) sanctioned by the NBD spec:

https://lists.gnu.org/archive/html/qemu-devel/2018-05/msg00135.html

--
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org