Backup and commit re-query the source block status for every task and
size a task by the copy buffer, so a long run of zeroes turns into a
crowd of small write-zeroes requests. This series reuses what the
up-front scan already learned and lets one write-zeroes task cover a
whole run.
Backup of a 16G qcow2 image holding 1G of data, the rest never
allocated, sync=full to a raw target on ext4:
tasks time
before 16384 1.6s
after 1088 1.0s
Such an image is the normal case rather than a corner one: a guest with
discard enabled on a disk which is mostly free leaves exactly this
shape behind.
v2, all from Andrey's review:
- 2/9: holes spelled out in both layouts, and zero runs added, so the
write-zeroes path of 3/9 is covered too
- 3/9: COMMIT_ZERO_CHUNK has a comment of its own saying what bounds it;
the cache check drops its dead half and asserts instead
- 4/9: a Case namedtuple pairs each size with its layout, and
create_image(), write_layout(), dirty_layout() and backup_and_check()
take out the duplication
- 8/9: g_assert_not_reached() for the sync mode which cannot reach there
- 9/9: a widened write-zeroes request only pays off where the target
zeroes by metadata. supported_zero_flags rules out the targets which
cannot, and the first widened request asks for BDRV_REQ_NO_FALLBACK to
settle the rest, since a driver may advertise it and only learn better
from a failing call. A target which would write the zeroes out fails
that request without writing, and the run keeps its requests at the
buffer chunk size from there on. With the size question settled that
way the cap became BDRV_REQUEST_MAX_BYTES rather than 256M.
- rebased on master
Signed-off-by: Denis V. Lunev <[email protected]>
CC: Vladimir Sementsov-Ogievskiy <[email protected]>
CC: John Snow <[email protected]>
CC: Andrey Drobyshev <[email protected]>
Denis V. Lunev (9):
block/commit: pass BDRV_WANT_PRECISE to block-status
iotests/040: cover large and fragmented commit runs
block/commit: batch block-status queries
iotests/124: cover backup of zero clusters and holes
block/block-copy: don't reserve memory for zero tasks
block/block-copy: extract block_copy_set_task_method()
block/block-copy: track known-zero source clusters
block/backup: pre-fill zero_bitmap for full/bitmap
block/block-copy: coalesce write-zeroes tasks
block/backup.c | 93 ++++++----
block/block-copy.c | 305 ++++++++++++++++++++++++++++----
block/commit.c | 58 +++++--
include/block/block-copy.h | 5 +
tests/qemu-iotests/040 | 102 ++++++++++-
tests/qemu-iotests/040.out | 4 +-
tests/qemu-iotests/124 | 344 ++++++++++++++++++++++++++++++++++++-
tests/qemu-iotests/124.out | 4 +-
8 files changed, 827 insertions(+), 88 deletions(-)
base-commit: 5f664cd37aec17e8145aa117d8da68f507edc8f1
--
2.53.0
