diff options
| author | Jean-Louis Dupond <jean-louis@dupond.be> | 2023-10-03 14:52:37 +0200 |
|---|---|---|
| committer | Hanna Czenczek <hreitz@redhat.com> | 2023-11-06 16:15:07 +0100 |
| commit | b2b109041ecd1095384f5be5bb9badd13c1cf286 (patch) | |
| tree | 3c6cc355936a8c74e356a86bc3b3526d0def0bc4 /qapi | |
| parent | 3e01f1147a16ca566694b97eafc941d62fa1e8d8 (diff) | |
qcow2: keep reference on zeroize with discard-no-unref enabled
When the discard-no-unref flag is enabled, we keep the reference for
normal discard requests.
But when a discard is executed on a snapshot/qcow2 image with backing,
the discards are saved as zero clusters in the snapshot image.
When committing the snapshot to the backing file, not
discard_in_l2_slice is called but zero_in_l2_slice. Which did not had
any logic to keep the reference when discard-no-unref is enabled.
Therefor we add logic in the zero_in_l2_slice call to keep the reference
on commit.
Fixes: https://gitlab.com/qemu-project/qemu/-/issues/1621
Signed-off-by: Jean-Louis Dupond <jean-louis@dupond.be>
Message-Id: <20231003125236.216473-2-jean-louis@dupond.be>
[hreitz: Made the documentation change more verbose, as discussed
on-list]
Signed-off-by: Hanna Czenczek <hreitz@redhat.com>
Diffstat (limited to 'qapi')
| -rw-r--r-- | qapi/block-core.json | 24 |
1 files changed, 14 insertions, 10 deletions
diff --git a/qapi/block-core.json b/qapi/block-core.json index 99961256f2..ca390c5700 100644 --- a/qapi/block-core.json +++ b/qapi/block-core.json @@ -3528,16 +3528,20 @@ # @pass-discard-other: whether discard requests for the data source # should be issued on other occasions where a cluster gets freed # -# @discard-no-unref: when enabled, discards from the guest will not -# cause cluster allocations to be relinquished. This prevents -# qcow2 fragmentation that would be caused by such discards. -# Besides potential performance degradation, such fragmentation -# can lead to increased allocation of clusters past the end of the -# image file, resulting in image files whose file length can grow -# much larger than their guest disk size would suggest. If image -# file length is of concern (e.g. when storing qcow2 images -# directly on block devices), you should consider enabling this -# option. (since 8.1) +# @discard-no-unref: when enabled, data clusters will remain +# preallocated when they are no longer used, e.g. because they are +# discarded or converted to zero clusters. As usual, whether the +# old data is discarded or kept on the protocol level (i.e. in the +# image file) depends on the setting of the pass-discard-request +# option. Keeping the clusters preallocated prevents qcow2 +# fragmentation that would otherwise be caused by freeing and +# re-allocating them later. Besides potential performance +# degradation, such fragmentation can lead to increased allocation +# of clusters past the end of the image file, resulting in image +# files whose file length can grow much larger than their guest disk +# size would suggest. If image file length is of concern (e.g. when +# storing qcow2 images directly on block devices), you should +# consider enabling this option. (since 8.1) # # @overlap-check: which overlap checks to perform for writes to the # image, defaults to 'cached' (since 2.2) |