From: Kevin Wolf <[email protected]> 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: [email protected] Signed-off-by: Kevin Wolf <[email protected]> Reviewed-by: Eric Blake <[email protected]> (cherry picked from commit f29fbf7c6b1c9a84f6931c1c222716fbe073e6e4) Signed-off-by: Michael Roth <[email protected]> --- block/qcow2.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/block/qcow2.c b/block/qcow2.c index 3ace3b2209..dfac74c264 100644 --- a/block/qcow2.c +++ b/block/qcow2.c @@ -2734,7 +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) { -- 2.17.1
