diff mbox series

[01/97] qcow2: Avoid COW during metadata preallocation

Message ID 20191001234616.7825-2-mdroth@linux.vnet.ibm.com
State New
Headers show
Series Patch Round-up for stable 4.0.1, freeze on 2019-10-10 | expand

Commit Message

Michael Roth Oct. 1, 2019, 11:44 p.m. UTC 
From: Kevin Wolf <kwolf@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-stable@nongnu.org
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
(cherry picked from commit f29fbf7c6b1c9a84f6931c1c222716fbe073e6e4)
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>
---
 block/qcow2.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
diff mbox series

Patch

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) {