| Message ID | 20230904150958.823365-1-jean-louis@dupond.be |
|---|---|
| State | New |
| Headers | show |
| Series | qcow2: keep reference on zeroize with discard-no-unref enabled | expand |
Replaced by PATCH v2. On 4/09/2023 17:09, Jean-Louis Dupond wrote: > 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. > > Next to that we also revert some logic from 42a2890a and just call > qcow2_free_any_cluster. As this will just decrease the refcount but not > remove the reference itself. And it will also send the discard further > to the lower layer. > > Fixes: https://gitlab.com/qemu-project/qemu/-/issues/1621 > Signed-off-by: Jean-Louis Dupond <jean-louis@dupond.be> > --- > block/qcow2-cluster.c | 18 +++++++----------- > 1 file changed, 7 insertions(+), 11 deletions(-) > > diff --git a/block/qcow2-cluster.c b/block/qcow2-cluster.c > index f4f6cd6ad0..48532ca3c2 100644 > --- a/block/qcow2-cluster.c > +++ b/block/qcow2-cluster.c > @@ -1975,16 +1975,7 @@ static int discard_in_l2_slice(BlockDriverState *bs, uint64_t offset, > if (has_subclusters(s)) { > set_l2_bitmap(s, l2_slice, l2_index + i, new_l2_bitmap); > } > - if (!keep_reference) { > - /* Then decrease the refcount */ > - qcow2_free_any_cluster(bs, old_l2_entry, type); > - } else if (s->discard_passthrough[type] && > - (cluster_type == QCOW2_CLUSTER_NORMAL || > - cluster_type == QCOW2_CLUSTER_ZERO_ALLOC)) { > - /* If we keep the reference, pass on the discard still */ > - bdrv_pdiscard(s->data_file, old_l2_entry & L2E_OFFSET_MASK, > - s->cluster_size); > - } > + qcow2_free_any_cluster(bs, old_l2_entry, type); > } > > qcow2_cache_put(s->l2_table_cache, (void **) &l2_slice); > @@ -2062,9 +2053,14 @@ zero_in_l2_slice(BlockDriverState *bs, uint64_t offset, > QCow2ClusterType type = qcow2_get_cluster_type(bs, old_l2_entry); > bool unmap = (type == QCOW2_CLUSTER_COMPRESSED) || > ((flags & BDRV_REQ_MAY_UNMAP) && qcow2_cluster_is_allocated(type)); > - uint64_t new_l2_entry = unmap ? 0 : old_l2_entry; > + uint64_t new_l2_entry = old_l2_entry; > uint64_t new_l2_bitmap = old_l2_bitmap; > > + if (unmap && > + !(s->discard_no_unref && type != QCOW2_CLUSTER_COMPRESSED)) { > + new_l2_entry = 0; > + } > + > if (has_subclusters(s)) { > new_l2_bitmap = QCOW_L2_BITMAP_ALL_ZEROES; > } else {
diff --git a/block/qcow2-cluster.c b/block/qcow2-cluster.c index f4f6cd6ad0..48532ca3c2 100644 --- a/block/qcow2-cluster.c +++ b/block/qcow2-cluster.c @@ -1975,16 +1975,7 @@ static int discard_in_l2_slice(BlockDriverState *bs, uint64_t offset, if (has_subclusters(s)) { set_l2_bitmap(s, l2_slice, l2_index + i, new_l2_bitmap); } - if (!keep_reference) { - /* Then decrease the refcount */ - qcow2_free_any_cluster(bs, old_l2_entry, type); - } else if (s->discard_passthrough[type] && - (cluster_type == QCOW2_CLUSTER_NORMAL || - cluster_type == QCOW2_CLUSTER_ZERO_ALLOC)) { - /* If we keep the reference, pass on the discard still */ - bdrv_pdiscard(s->data_file, old_l2_entry & L2E_OFFSET_MASK, - s->cluster_size); - } + qcow2_free_any_cluster(bs, old_l2_entry, type); } qcow2_cache_put(s->l2_table_cache, (void **) &l2_slice); @@ -2062,9 +2053,14 @@ zero_in_l2_slice(BlockDriverState *bs, uint64_t offset, QCow2ClusterType type = qcow2_get_cluster_type(bs, old_l2_entry); bool unmap = (type == QCOW2_CLUSTER_COMPRESSED) || ((flags & BDRV_REQ_MAY_UNMAP) && qcow2_cluster_is_allocated(type)); - uint64_t new_l2_entry = unmap ? 0 : old_l2_entry; + uint64_t new_l2_entry = old_l2_entry; uint64_t new_l2_bitmap = old_l2_bitmap; + if (unmap && + !(s->discard_no_unref && type != QCOW2_CLUSTER_COMPRESSED)) { + new_l2_entry = 0; + } + if (has_subclusters(s)) { new_l2_bitmap = QCOW_L2_BITMAP_ALL_ZEROES; } else {
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. Next to that we also revert some logic from 42a2890a and just call qcow2_free_any_cluster. As this will just decrease the refcount but not remove the reference itself. And it will also send the discard further to the lower layer. Fixes: https://gitlab.com/qemu-project/qemu/-/issues/1621 Signed-off-by: Jean-Louis Dupond <jean-louis@dupond.be> --- block/qcow2-cluster.c | 18 +++++++----------- 1 file changed, 7 insertions(+), 11 deletions(-)