From: Kevin Wolf <kw...@redhat.com> 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> Reviewed-by: Eric Blake <ebl...@redhat.com> (cherry picked from commit f29fbf7c6b1c9a84f6931c1c222716fbe073e6e4) *modified to avoid functional dependency on 93e32b3e Signed-off-by: Michael Roth <mdr...@linux.vnet.ibm.com> --- block/qcow2.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/block/qcow2.c b/block/qcow2.c index 991d6ac91b..6ddaf9a1f8 100644 --- a/block/qcow2.c +++ b/block/qcow2.c @@ -2590,6 +2590,7 @@ 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; @@ -2600,7 +2601,7 @@ 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) { -- 2.17.1