On 05/14/2016 06:01 AM, Denis V. Lunev wrote: > We should split requests even if they are less than write_zeroes_alignment. > For example we can have the following request: > offset 62k > size 4k > write_zeroes_alignment 64k > Original code will send 1 request covering 2 qcow2 clusters. One cluster > could be zeroed as a whole, another could not be. In this case we will have > both 2 clusters allocated. > > After the patch 2 requests to qcow2 layer will be sent and thus only one > cluster will be allocated.
Grammar suggestion:
The original code sent 1 request covering 2 qcow2 clusters, and resulted
in both clusters being allocated. But by splitting the request, we can
cater to the case where one of the two clusters can be zeroed as a
whole, for only 1 cluster allocated after the operation.
>
> Signed-off-by: Denis V. Lunev <d...@openvz.org>
> CC: Kevin Wolf <kw...@redhat.com>
> ---
> block/io.c | 6 +++---
> 1 file changed, 3 insertions(+), 3 deletions(-)
>
> num -= sector_num % bs->bl.write_zeroes_alignment;
> - } else if ((sector_num + num) % bs->bl.write_zeroes_alignment !=
> 0) {
> + } else if (num > bs->bl.write_zeroes_alignment &&
> + (sector_num + num) % bs->bl.write_zeroes_alignment != 0)
> {
Alignment looks off. Also, if it were me, I'd write 'a % b' rather than
'a % b != 0'.
--
Eric Blake eblake redhat com +1-919-301-3266
Libvirt virtualization library http://libvirt.org
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