Limiting the allocation to INT_MAX bytes isn't particularly clever
because it means that the final cluster will be a partial cluster which
will be completed through a COW operation. This results in unnecessary
data read and write requests which lead to an unwanted non-sparse
filesystem block for metadata preallocation.
Align the maximum allocation size down to the cluster size to avoid this
situation.
Cc: qemu-sta...@nongnu.org
Signed-off-by: Kevin Wolf <kw...@redhat.com>
---
block/qcow2.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/block/qcow2.c b/block/qcow2.c
index d507ee0686..c8400e9712 100644
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -2723,6 +2723,7 @@ static int qcow2_set_up_encryption(BlockDriverState *bs,
static int coroutine_fn preallocate_co(BlockDriverState *bs, uint64_t offset,
uint64_t new_length)
{
+ BDRVQcow2State *s = bs->opaque;
uint64_t bytes;
uint64_t host_offset = 0;
unsigned int cur_bytes;
@@ -2733,7 +2734,7 @@ static int coroutine_fn preallocate_co(BlockDriverState
*bs, uint64_t offset,
bytes = new_length - offset;
while (bytes) {
- cur_bytes = MIN(bytes, INT_MAX);
+ cur_bytes = MIN(bytes, QEMU_ALIGN_DOWN(INT_MAX, s->cluster_size));
ret = qcow2_alloc_cluster_offset(bs, offset, &cur_bytes,
&host_offset, &meta);
if (ret < 0) {
--
2.20.1
