Changes in v2:
- introduce new BDRV flag for write_zeroes()
instead of using driver callback directly.
Skipped introducing new functions like bdrv_co_pallocate() for now:
1. it seems ok to keep calling this write_zeroes() as zeroes
are expected;
2. most of the code can be reused now anyway, so changes to
write_zeroes() path are not significant
3. write_zeroes() alignment and max-request limits can also be reused
As a possible alternative we can have bdrv_co_pallocate() which can
switch to pwrite_zeroes(,flags|=BDRV_REQ_ALLOCATE) early.
========
This pull request is to address a few performance problems of qcow2 format:
1. non cluster-aligned write requests (to unallocated clusters) explicitly
pad data with zeroes if there is no backing data. This can be avoided
and the whole clusters are preallocated and zeroed in a single
efficient write_zeroes() operation, also providing better host file
continuity
2. moreover, efficient write_zeroes() operation can be used to preallocate
space megabytes ahead which gives noticeable improvement on some storage
types (e.g. distributed storages where space allocation operation is
expensive)
3. preallocating/zeroing the clusters in advance makes possible to enable
simultaneous writes to the same unallocated cluster, which is beneficial
for parallel sequential write operations which are not cluster-aligned
Performance test results are added to commit messages (see patch 3, 12)
Anton Nefedov (11):
block: introduce BDRV_REQ_ALLOCATE flag
file-posix: support BDRV_REQ_ALLOCATE
blkdebug: support BDRV_REQ_ALLOCATE
qcow2: do not COW the empty areas
qcow2: set inactive flag
qcow2: handle_prealloc(): find out if area zeroed by earlier
preallocation
qcow2: fix misleading comment about L2 linking
qcow2-cluster: slightly refactor handle_dependencies()
qcow2-cluster: make handle_dependencies() logic easier to follow
qcow2: allow concurrent unaligned writes to the same clusters
iotest 046: test simultaneous cluster write error case
Denis V. Lunev (3):
qcow2: alloc space for COW in one chunk
qcow2: preallocation at image expand
qcow2: truncate preallocated space
Pavel Butsykin (1):
qcow2: check space leak at the end of the image
block/blkdebug.c | 3 +-
block/file-posix.c | 9 +-
block/io.c | 19 ++-
block/qcow2-cache.c | 3 +
block/qcow2-cluster.c | 218 +++++++++++++++++++++++------
block/qcow2-refcount.c | 21 +++
block/qcow2.c | 273 ++++++++++++++++++++++++++++++++++++-
block/qcow2.h | 26 ++++
block/trace-events | 1 +
include/block/block.h | 6 +-
tests/qemu-iotests/026.out | 104 ++++++++++----
tests/qemu-iotests/026.out.nocache | 104 ++++++++++----
tests/qemu-iotests/029.out | 5 +-
tests/qemu-iotests/046 | 38 +++++-
tests/qemu-iotests/046.out | 23 ++++
tests/qemu-iotests/060 | 2 +-
tests/qemu-iotests/060.out | 13 +-
tests/qemu-iotests/061.out | 5 +-
tests/qemu-iotests/066 | 2 +-
tests/qemu-iotests/066.out | 9 +-
tests/qemu-iotests/098.out | 7 +-
tests/qemu-iotests/108.out | 5 +-
tests/qemu-iotests/112.out | 5 +-
23 files changed, 789 insertions(+), 112 deletions(-)
--
2.7.4
