On 20.10.23 23:56, Andrey Drobyshev wrote:
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. Signed-off-by: Andrey Drobyshev <andrey.drobys...@virtuozzo.com> --- block/qcow2-cluster.c | 100 ++++++++++++++++++++++++++++++++++++++++-- block/qcow2.c | 8 ++-- 2 files changed, 101 insertions(+), 7 deletions(-) diff --git a/block/qcow2-cluster.c b/block/qcow2-cluster.c index 7c6fa5524c..cf40f2dc12 100644 --- a/block/qcow2-cluster.c +++ b/block/qcow2-cluster.c @@ -2042,6 +2042,74 @@ discard_in_l2_slice(BlockDriverState *bs, uint64_t offset, uint64_t nb_clusters, return nb_clusters; }+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, + SubClusterRangeInfo *pscri) +{ + BDRVQcow2State *s = bs->opaque; + uint64_t new_l2_bitmap, l2_bitmap_mask; + int ret, sc = offset_to_sc_index(s, offset); + SubClusterRangeInfo scri = { 0 }; + + if (!pscri) { + ret = get_sc_range_info(bs, offset, nb_subclusters, &scri); + if (ret < 0) { + goto out; + } + } else { + scri = *pscri; + } + + l2_bitmap_mask = QCOW_OFLAG_SUB_ALLOC_RANGE(sc, sc + nb_subclusters); + new_l2_bitmap = scri.l2_bitmap; + new_l2_bitmap &= ~l2_bitmap_mask; + + /* + * If there're no allocated subclusters left, we might as well discard + * the entire cluster. That way we'd also update the refcount table. + */ + if (!(new_l2_bitmap & QCOW_L2_BITMAP_ALL_ALLOC)) { + return discard_in_l2_slice(bs, + QEMU_ALIGN_DOWN(offset, s->cluster_size), + 1, type, full_discard); + }
scri.l2_slice is leaked here. Hanna
