Re: [Qemu-devel] [PATCH 0/4] qcow2: Save another common flush

[Anthony Liguori]

On 09/17/2010 11:18 AM, Kevin Wolf wrote:
> For copy on write (this includes any cluster allocations that don't fill the
> whole cluster with one request), what qcow2 does looks like this:
>
> 1. Allocate new clusters (increase refcounts)
> 2. bdrv_flush
> 3. Copy sectors before the first touched one
> 4. bdrv_flush
> 5. Copy sectors after the last touched one
> 6. bdrv_flush
> 7. Update the L2 table to point to the new clusters
>
> Step 2 and 4 are not necessary. This series moves flushes around to get all
> of these three bdrv_flush calls merged into one.
>    

Makes sense to me.

Regards,

Anthony Liguori

> Kevin Wolf (4):
>    qcow2: Move sync out of write_refcount_block_entries
>    qcow2: Move sync out of update_refcount
>    qcow2: Move sync out of qcow2_alloc_clusters
>    qcow2: Get rid of additional sync on COW
>
>   block/qcow2-cluster.c  |   11 ++++++++++-
>   block/qcow2-refcount.c |   13 ++++++++++++-
>   block/qcow2-snapshot.c |    2 ++
>   3 files changed, 24 insertions(+), 2 deletions(-)
>
>