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
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: Eric Blake <ebl...@redhat.com>
CC: Kevin Wolf <kw...@redhat.com>
---
block/io.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/block/io.c b/block/io.c
index cd6d71a..6a24ea8 100644
--- a/block/io.c
+++ b/block/io.c
@@ -1172,13 +1172,13 @@ static int coroutine_fn
bdrv_co_do_write_zeroes(BlockDriverState *bs,
/* Align request. Block drivers can expect the "bulk" of the request
* to be aligned.
*/
- if (bs->bl.write_zeroes_alignment
- && num > bs->bl.write_zeroes_alignment) {
+ if (bs->bl.write_zeroes_alignment) {
if (sector_num % bs->bl.write_zeroes_alignment != 0) {
/* Make a small request up to the first aligned sector. */
num = bs->bl.write_zeroes_alignment;
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) {
/* Shorten the request to the last aligned sector. num cannot
* underflow because num > bs->bl.write_zeroes_alignment.
*/
--
2.1.4
