This commit makes the discard operation work on the subcluster level
rather than cluster level. It introduces discard_l2_subclusters()
function and makes use of it in qcow2 discard implementation, much like
it's done with zero_in_l2_slice() / zero_l2_subclusters(). It also
changes the qcow2 driver pdiscard_alignment to subcluster_size. That
way subcluster-aligned discards lead to actual fallocate(PUNCH_HOLE)
operation and free host disk space.
This feature will let us gain additional disk space on guest
TRIM/discard requests, especially when using large enough clusters
(1M, 2M) with subclusters enabled.
Also rename qcow2_cluster_discard() -> qcow2_subcluster_discard() to
reflect the change.
Signed-off-by: Andrey Drobyshev <andrey.drobys...@virtuozzo.com>
---
block/qcow2-cluster.c | 106 +++++++++++++++++++++++++++++++++++++----
block/qcow2-snapshot.c | 6 +--
block/qcow2.c | 25 +++++-----
block/qcow2.h | 4 +-
tests/qemu-iotests/271 | 2 +-
5 files changed, 117 insertions(+), 26 deletions(-)
diff --git a/block/qcow2-cluster.c b/block/qcow2-cluster.c
index 8d39e2f960..3c134a7e80 100644
--- a/block/qcow2-cluster.c
+++ b/block/qcow2-cluster.c
@@ -2105,25 +2105,106 @@ discard_in_l2_slice(BlockDriverState *bs, uint64_t
offset, uint64_t nb_clusters,
return nb_clusters;
}
-int qcow2_cluster_discard(BlockDriverState *bs, uint64_t offset,
- uint64_t bytes, enum qcow2_discard_type type,
- bool full_discard)
+static int coroutine_fn GRAPH_RDLOCK
+discard_l2_subclusters(BlockDriverState *bs, uint64_t offset,
+ uint64_t nb_subclusters,
+ enum qcow2_discard_type type,
+ bool full_discard)
+{
+ BDRVQcow2State *s = bs->opaque;
+ uint64_t new_l2_bitmap, bitmap_alloc_mask, bitmap_zero_mask;
+ int ret, sc = offset_to_sc_index(s, offset);
+ g_auto(SubClusterRangeInfo) scri = { 0 };
+
+ ret = get_sc_range_info(bs, offset, nb_subclusters, &scri);
+ if (ret < 0) {
+ return ret;
+ }
+
+ new_l2_bitmap = scri.l2_bitmap;
+ bitmap_alloc_mask = QCOW_OFLAG_SUB_ALLOC_RANGE(sc, sc + nb_subclusters);
+ bitmap_zero_mask = QCOW_OFLAG_SUB_ZERO_RANGE(sc, sc + nb_subclusters);
+
+ new_l2_bitmap &= ~bitmap_alloc_mask;
+
+ /*
+ * Full discard means we fall through to the backing file, thus we need
+ * to mark the subclusters as deallocated and clear the corresponding
+ * zero bits.
+ *
+ * Non-full discard means subclusters should be explicitly marked as
+ * zeroes. In this case QCOW2 specification requires the corresponding
+ * allocation status bits to be unset as well. If the subclusters are
+ * deallocated in the first place and there's no backing, the operation
+ * can be skipped.
+ */
+ if (full_discard) {
+ new_l2_bitmap &= ~bitmap_zero_mask;
+ } else if (bs->backing || scri.l2_bitmap & bitmap_alloc_mask) {
+ new_l2_bitmap |= bitmap_zero_mask;
+ }
+
+ /*
+ * If after discarding this range there won't be any allocated subclusters
+ * left, and new bitmap becomes the same as it'd be after discarding the
+ * whole cluster, we better discard it entirely. That way we'd also
+ * update the refcount table.
+ */
+ if ((full_discard && new_l2_bitmap == 0) ||
+ (!full_discard && new_l2_bitmap == QCOW_L2_BITMAP_ALL_ZEROES)) {
+ return discard_in_l2_slice(
+ bs, QEMU_ALIGN_DOWN(offset, s->cluster_size),
+ 1, type, full_discard);
+ }
+
+ if (scri.l2_bitmap != new_l2_bitmap) {
+ set_l2_bitmap(s, scri.l2_slice, scri.l2_index, new_l2_bitmap);
+ qcow2_cache_entry_mark_dirty(s->l2_table_cache, scri.l2_slice);
+ }
+
+ discard_no_unref_any_file(
+ bs, (scri.l2_entry & L2E_OFFSET_MASK) + offset_into_cluster(s, offset),
+ nb_subclusters * s->subcluster_size, scri.ctype, type);
+
+ return 0;
+}
+
+int qcow2_subcluster_discard(BlockDriverState *bs, uint64_t offset,
+ uint64_t bytes, enum qcow2_discard_type type,
+ bool full_discard)
{
BDRVQcow2State *s = bs->opaque;
uint64_t end_offset = offset + bytes;
uint64_t nb_clusters;
+ unsigned head, tail;
int64_t cleared;
int ret;
/* Caller must pass aligned values, except at image end */
- assert(QEMU_IS_ALIGNED(offset, s->cluster_size));
- assert(QEMU_IS_ALIGNED(end_offset, s->cluster_size) ||
+ assert(QEMU_IS_ALIGNED(offset, s->subcluster_size));
+ assert(QEMU_IS_ALIGNED(end_offset, s->subcluster_size) ||
end_offset == bs->total_sectors << BDRV_SECTOR_BITS);
- nb_clusters = size_to_clusters(s, bytes);
+ head = MIN(end_offset, ROUND_UP(offset, s->cluster_size)) - offset;
+ offset += head;
+
+ tail = (end_offset >= bs->total_sectors << BDRV_SECTOR_BITS) ? 0 :
+ end_offset - MAX(offset, start_of_cluster(s, end_offset));
+ end_offset -= tail;
s->cache_discards = true;
+ if (head) {
+ ret = discard_l2_subclusters(bs, offset - head,
+ size_to_subclusters(s, head), type,
+ full_discard);
+ if (ret < 0) {
+ goto fail;
+ }
+ }
+
+ nb_clusters = size_to_clusters(s, end_offset - offset);
+
/* Each L2 slice is handled by its own loop iteration */
while (nb_clusters > 0) {
cleared = discard_in_l2_slice(bs, offset, nb_clusters, type,
@@ -2137,6 +2218,15 @@ int qcow2_cluster_discard(BlockDriverState *bs, uint64_t
offset,
offset += (cleared * s->cluster_size);
}
+ if (tail) {
+ ret = discard_l2_subclusters(bs, end_offset,
+ size_to_subclusters(s, tail), type,
+ full_discard);
+ if (ret < 0) {
+ goto fail;
+ }
+ }
+
ret = 0;
fail:
s->cache_discards = false;
@@ -2286,8 +2376,8 @@ int coroutine_fn
qcow2_subcluster_zeroize(BlockDriverState *bs, uint64_t offset,
*/
if (s->qcow_version < 3) {
if (!bs->backing) {
- return qcow2_cluster_discard(bs, offset, bytes,
- QCOW2_DISCARD_REQUEST, false);
+ return qcow2_subcluster_discard(bs, offset, bytes,
+ QCOW2_DISCARD_REQUEST, false);
}
return -ENOTSUP;
}
diff --git a/block/qcow2-snapshot.c b/block/qcow2-snapshot.c
index 92e47978bf..4e39354d02 100644
--- a/block/qcow2-snapshot.c
+++ b/block/qcow2-snapshot.c
@@ -736,9 +736,9 @@ int qcow2_snapshot_create(BlockDriverState *bs,
QEMUSnapshotInfo *sn_info)
/* The VM state isn't needed any more in the active L1 table; in fact, it
* hurts by causing expensive COW for the next snapshot. */
- qcow2_cluster_discard(bs, qcow2_vm_state_offset(s),
- ROUND_UP(sn->vm_state_size, s->cluster_size),
- QCOW2_DISCARD_NEVER, false);
+ qcow2_subcluster_discard(bs, qcow2_vm_state_offset(s),
+ ROUND_UP(sn->vm_state_size, s->cluster_size),
+ QCOW2_DISCARD_NEVER, false);
#ifdef DEBUG_ALLOC
{
diff --git a/block/qcow2.c b/block/qcow2.c
index 956128b409..792b106eb6 100644
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -1967,7 +1967,7 @@ static void qcow2_refresh_limits(BlockDriverState *bs,
Error **errp)
bs->bl.request_alignment = qcrypto_block_get_sector_size(s->crypto);
}
bs->bl.pwrite_zeroes_alignment = s->subcluster_size;
- bs->bl.pdiscard_alignment = s->cluster_size;
+ bs->bl.pdiscard_alignment = s->subcluster_size;
}
static int GRAPH_UNLOCKED
@@ -4112,19 +4112,19 @@ qcow2_co_pdiscard(BlockDriverState *bs, int64_t offset,
int64_t bytes)
return -ENOTSUP;
}
- if (!QEMU_IS_ALIGNED(offset | bytes, s->cluster_size)) {
- assert(bytes < s->cluster_size);
+ if (!QEMU_IS_ALIGNED(offset | bytes, bs->bl.pdiscard_alignment)) {
+ assert(bytes < bs->bl.pdiscard_alignment);
/* Ignore partial clusters, except for the special case of the
* complete partial cluster at the end of an unaligned file */
- if (!QEMU_IS_ALIGNED(offset, s->cluster_size) ||
+ if (!QEMU_IS_ALIGNED(offset, bs->bl.pdiscard_alignment) ||
offset + bytes != bs->total_sectors * BDRV_SECTOR_SIZE) {
return -ENOTSUP;
}
}
qemu_co_mutex_lock(&s->lock);
- ret = qcow2_cluster_discard(bs, offset, bytes, QCOW2_DISCARD_REQUEST,
- false);
+ ret = qcow2_subcluster_discard(bs, offset, bytes, QCOW2_DISCARD_REQUEST,
+ false);
qemu_co_mutex_unlock(&s->lock);
return ret;
}
@@ -4335,10 +4335,10 @@ qcow2_co_truncate(BlockDriverState *bs, int64_t offset,
bool exact,
goto fail;
}
- ret = qcow2_cluster_discard(bs, ROUND_UP(offset, s->cluster_size),
- old_length - ROUND_UP(offset,
- s->cluster_size),
- QCOW2_DISCARD_ALWAYS, true);
+ ret = qcow2_subcluster_discard(bs, ROUND_UP(offset, s->cluster_size),
+ old_length - ROUND_UP(offset,
+ s->cluster_size),
+ QCOW2_DISCARD_ALWAYS, true);
if (ret < 0) {
error_setg_errno(errp, -ret, "Failed to discard cropped clusters");
goto fail;
@@ -5032,8 +5032,9 @@ static int GRAPH_RDLOCK qcow2_make_empty(BlockDriverState
*bs)
* default action for this kind of discard is to pass the discard,
* which will ideally result in an actually smaller image file, as
* is probably desired. */
- ret = qcow2_cluster_discard(bs, offset, MIN(step, end_offset - offset),
- QCOW2_DISCARD_SNAPSHOT, true);
+ ret = qcow2_subcluster_discard(bs, offset,
+ MIN(step, end_offset - offset),
+ QCOW2_DISCARD_SNAPSHOT, true);
if (ret < 0) {
break;
}
diff --git a/block/qcow2.h b/block/qcow2.h
index 197bdcdf53..a65c185b51 100644
--- a/block/qcow2.h
+++ b/block/qcow2.h
@@ -953,8 +953,8 @@ void coroutine_fn GRAPH_RDLOCK
qcow2_alloc_cluster_abort(BlockDriverState *bs, QCowL2Meta *m);
int GRAPH_RDLOCK
-qcow2_cluster_discard(BlockDriverState *bs, uint64_t offset, uint64_t bytes,
- enum qcow2_discard_type type, bool full_discard);
+qcow2_subcluster_discard(BlockDriverState *bs, uint64_t offset, uint64_t bytes,
+ enum qcow2_discard_type type, bool full_discard);
int coroutine_fn GRAPH_RDLOCK
qcow2_subcluster_zeroize(BlockDriverState *bs, uint64_t offset, uint64_t bytes,
diff --git a/tests/qemu-iotests/271 b/tests/qemu-iotests/271
index 59a6fafa2f..04c57813c2 100755
--- a/tests/qemu-iotests/271
+++ b/tests/qemu-iotests/271
@@ -518,7 +518,7 @@ done
############################################################
############################################################
-# Test qcow2_cluster_discard() with full and normal discards
+# Test qcow2_subcluster_discard() with full and normal discards
for use_backing_file in yes no; do
echo
echo "### Discarding clusters with non-zero bitmaps (backing file:
$use_backing_file) ###"
--
2.39.3
