qcow2: Batch discards
This optimises the discard operation for freed clusters by batching
discard requests (both snapshot deletion and bdrv_discard end up
updating the refcounts cluster by cluster).
Note that we don't discard asynchronously, but keep s->lock held. This
is to avoid that a freed cluster is reallocated and written to while the
discard is still in flight.
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
diff --git a/block/qcow2-cluster.c b/block/qcow2-cluster.c
index 3191d6b..cca76d4 100644
--- a/block/qcow2-cluster.c
+++ b/block/qcow2-cluster.c
@@ -1377,18 +1377,25 @@
nb_clusters = size_to_clusters(s, end_offset - offset);
+ s->cache_discards = true;
+
/* Each L2 table is handled by its own loop iteration */
while (nb_clusters > 0) {
ret = discard_single_l2(bs, offset, nb_clusters);
if (ret < 0) {
- return ret;
+ goto fail;
}
nb_clusters -= ret;
offset += (ret * s->cluster_size);
}
- return 0;
+ ret = 0;
+fail:
+ s->cache_discards = false;
+ qcow2_process_discards(bs, ret);
+
+ return ret;
}
/*
@@ -1450,15 +1457,22 @@
/* Each L2 table is handled by its own loop iteration */
nb_clusters = size_to_clusters(s, nb_sectors << BDRV_SECTOR_BITS);
+ s->cache_discards = true;
+
while (nb_clusters > 0) {
ret = zero_single_l2(bs, offset, nb_clusters);
if (ret < 0) {
- return ret;
+ goto fail;
}
nb_clusters -= ret;
offset += (ret * s->cluster_size);
}
- return 0;
+ ret = 0;
+fail:
+ s->cache_discards = false;
+ qcow2_process_discards(bs, ret);
+
+ return ret;
}
