@@ -1015,16 +1015,16 @@ static int handle_alloc(BlockDriverState *bs, uint64_t guest_offset,
nb_clusters = count_cow_clusters(s, nb_clusters, l2_table, l2_index);
}
+ /* This function is only called when there were no non-COW clusters, so if
+ * we can't find any unallocated or COW clusters either, something is
+ * wrong with our code. */
+ assert(nb_clusters > 0);
+
ret = qcow2_cache_put(bs, s->l2_table_cache, (void**) &l2_table);
if (ret < 0) {
return ret;
}
- if (nb_clusters == 0) {
- *bytes = 0;
- return 0;
- }
-
/* Allocate, if necessary at a given offset in the image file */
alloc_cluster_offset = *host_offset;
ret = do_alloc_cluster_offset(bs, guest_offset, &alloc_cluster_offset,
@@ -1139,8 +1139,27 @@ again:
remaining = (n_end - n_start) << BDRV_SECTOR_BITS;
cluster_offset = 0;
*host_offset = 0;
+ cur_bytes = 0;
+ *m = NULL;
while (true) {
+
+ if (!*host_offset) {
+ *host_offset = start_of_cluster(s, cluster_offset);
+ }
+
+ assert(remaining >= cur_bytes);
+
+ start += cur_bytes;
+ remaining -= cur_bytes;
+ cluster_offset += cur_bytes;
+
+ if (remaining == 0) {
+ break;
+ }
+
+ cur_bytes = remaining;
+
/*
* Now start gathering as many contiguous clusters as possible:
*
@@ -1159,9 +1178,12 @@ again:
* the right synchronisation between the in-flight request and
* the new one.
*/
- cur_bytes = remaining;
ret = handle_dependencies(bs, start, &cur_bytes);
if (ret == -EAGAIN) {
+ /* Currently handle_dependencies() doesn't yield if we already had
+ * an allocation. If it did, we would have to clean up the L2Meta
+ * structs before starting over. */
+ assert(*m == NULL);
goto again;
} else if (ret < 0) {
return ret;
@@ -1178,24 +1200,11 @@ again:
if (ret < 0) {
return ret;
} else if (ret) {
- if (!*host_offset) {
- *host_offset = cluster_offset;
- }
-
- start += cur_bytes;
- remaining -= cur_bytes;
- cluster_offset += cur_bytes;
-
- cur_bytes = remaining;
+ continue;
} else if (cur_bytes == 0) {
break;
}
- /* If there is something left to allocate, do that now */
- if (remaining == 0) {
- break;
- }
-
/*
* 3. If the request still hasn't completed, allocate new clusters,
* considering any cluster_offset of steps 1c or 2.
@@ -1204,15 +1213,7 @@ again:
if (ret < 0) {
return ret;
} else if (ret) {
- if (!*host_offset) {
- *host_offset = cluster_offset;
- }
-
- start += cur_bytes;
- remaining -= cur_bytes;
- cluster_offset += cur_bytes;
-
- break;
+ continue;
} else {
assert(cur_bytes == 0);
break;
@@ -1,6 +1,6 @@
No errors were found on the image.
7292415/33554432 = 21.73% allocated, 0.00% fragmented, 0.00% compressed clusters
-Image end offset: 4296447488
+Image end offset: 4296448000
.
----------------------------------------------------------------------
Ran 1 tests
Instead of just checking once in exactly this order if there are dependendies, non-COW clusters and new allocation, this starts looping around these. This way we can, for example, gather non-COW clusters after new allocations as long as the host cluster offsets stay contiguous. Once handle_dependencies() is extended so that COW areas of in-flight allocations can be overwritten, this allows to continue with gathering other clusters (we wouldn't be able to do that without this change because we would have missed a possible second dependency in one of the next clusters). This means that in the typical sequential write case, we can combine the COW overwrite of one cluster with the allocation of the next cluster as soon as something like Delayed COW gets actually implemented. It is only by avoiding splitting requests this way that Delayed COW actually starts improving performance noticably. Signed-off-by: Kevin Wolf <kwolf@redhat.com> --- block/qcow2-cluster.c | 59 +++++++++++++++++++++++----------------------- tests/qemu-iotests/044.out | 2 +- 2 files changed, 31 insertions(+), 30 deletions(-)