Properly setting the metadata cache size can provide better performance
in case of using big qcow2 images.
This patch introduces two driver options:
* driver.metadata_cache.max_size
* driver.metadata_cache.max_size.unit
E.g. --disk ...,driver.type=qcow2,\
driver.metadata_cache.max_size=2,\
driver.metadata_cache.max_size.unit=MiB
BTW, Metadata cache size control is currently supported only for qcow2.
Regarding how to properly caluclate the cache size of qcow2, Please refer
to qemu's documentation.
Signed-off-by: Lin Ma <lma@suse.com>
11a887ece5