qcow2: Avoid COW during metadata preallocation
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-stable@nongnu.org
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
(cherry picked from commit f29fbf7c6b
)
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>
stable-4.0
parent
131b9a0570
commit
5669ef1e6c
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@ -2734,7 +2734,7 @@ static int coroutine_fn preallocate_co(BlockDriverState *bs, uint64_t offset,
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bytes = new_length - offset;
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while (bytes) {
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cur_bytes = MIN(bytes, INT_MAX);
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cur_bytes = MIN(bytes, QEMU_ALIGN_DOWN(INT_MAX, s->cluster_size));
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ret = qcow2_alloc_cluster_offset(bs, offset, &cur_bytes,
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&host_offset, &meta);
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if (ret < 0) {
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