@@ -3215,6 +3215,8 @@
#
# @cor_write: a write due to copy-on-read (since 2.11)
#
+# @cluster_alloc_space: an allocation of file space for a cluster (since 4.1)
+#
# Since: 2.9
##
{ 'enum': 'BlkdebugEvent', 'prefix': 'BLKDBG',
@@ -3233,7 +3235,7 @@
'pwritev_rmw_tail', 'pwritev_rmw_after_tail', 'pwritev',
'pwritev_zero', 'pwritev_done', 'empty_image_prepare',
'l1_shrink_write_table', 'l1_shrink_free_l2_clusters',
- 'cor_write'] }
+ 'cor_write', 'cluster_alloc_space'] }
##
# @BlkdebugInjectErrorOptions:
@@ -398,6 +398,12 @@ typedef struct QCowL2Meta
*/
Qcow2COWRegion cow_end;
+ /*
+ * Indicates that COW regions are already handled and do not require
+ * any more processing.
+ */
+ bool skip_cow;
+
/**
* The I/O vector with the data from the actual guest write request.
* If non-NULL, this is meant to be merged together with the data
@@ -832,7 +832,7 @@ static int perform_cow(BlockDriverState *bs, QCowL2Meta *m)
assert(start->offset + start->nb_bytes <= end->offset);
assert(!m->data_qiov || m->data_qiov->size == data_bytes);
- if (start->nb_bytes == 0 && end->nb_bytes == 0) {
+ if ((start->nb_bytes == 0 && end->nb_bytes == 0) || m->skip_cow) {
return 0;
}
@@ -2120,6 +2120,11 @@ static bool merge_cow(uint64_t offset, unsigned bytes,
continue;
}
+ /* If COW regions are handled already, skip this too */
+ if (m->skip_cow) {
+ continue;
+ }
+
/* The data (middle) region must be immediately after the
* start region */
if (l2meta_cow_start(m) + m->cow_start.nb_bytes != offset) {
@@ -2145,6 +2150,80 @@ static bool merge_cow(uint64_t offset, unsigned bytes,
return false;
}
+static bool is_unallocated(BlockDriverState *bs, int64_t offset, int64_t bytes)
+{
+ int64_t nr;
+ return !bytes ||
+ (!bdrv_is_allocated_above(bs, NULL, offset, bytes, &nr) && nr == bytes);
+}
+
+static bool is_zero_cow(BlockDriverState *bs, QCowL2Meta *m)
+{
+ /*
+ * This check is designed for optimization shortcut so it must be
+ * efficient.
+ * Instead of is_zero(), use is_unallocated() as it is faster (but not
+ * as accurate and can result in false negatives).
+ */
+ return is_unallocated(bs, m->offset + m->cow_start.offset,
+ m->cow_start.nb_bytes) &&
+ is_unallocated(bs, m->offset + m->cow_end.offset,
+ m->cow_end.nb_bytes);
+}
+
+static int handle_alloc_space(BlockDriverState *bs, QCowL2Meta *l2meta)
+{
+ BDRVQcow2State *s = bs->opaque;
+ QCowL2Meta *m;
+
+ if (!(s->data_file->bs->supported_zero_flags & BDRV_REQ_NO_FALLBACK)) {
+ return 0;
+ }
+
+ if (bs->encrypted) {
+ return 0;
+ }
+
+ for (m = l2meta; m != NULL; m = m->next) {
+ int ret;
+
+ if (!m->cow_start.nb_bytes && !m->cow_end.nb_bytes) {
+ continue;
+ }
+
+ if (!is_zero_cow(bs, m)) {
+ continue;
+ }
+
+ /*
+ * instead of writing zero COW buffers,
+ * efficiently zero out the whole clusters
+ */
+
+ ret = qcow2_pre_write_overlap_check(bs, 0, m->alloc_offset,
+ m->nb_clusters * s->cluster_size,
+ true);
+ if (ret < 0) {
+ return ret;
+ }
+
+ BLKDBG_EVENT(bs->file, BLKDBG_CLUSTER_ALLOC_SPACE);
+ ret = bdrv_co_pwrite_zeroes(s->data_file, m->alloc_offset,
+ m->nb_clusters * s->cluster_size,
+ BDRV_REQ_NO_FALLBACK);
+ if (ret < 0) {
+ if (ret != -ENOTSUP && ret != -EAGAIN) {
+ return ret;
+ }
+ continue;
+ }
+
+ trace_qcow2_skip_cow(qemu_coroutine_self(), m->offset, m->nb_clusters);
+ m->skip_cow = true;
+ }
+ return 0;
+}
+
static coroutine_fn int qcow2_co_pwritev(BlockDriverState *bs, uint64_t offset,
uint64_t bytes, QEMUIOVector *qiov,
int flags)
@@ -2225,24 +2304,34 @@ static coroutine_fn int qcow2_co_pwritev(BlockDriverState *bs, uint64_t offset,
goto fail;
}
+ qemu_co_mutex_unlock(&s->lock);
+
+ /* Try to efficiently initialize the physical space with zeroes */
+ ret = handle_alloc_space(bs, l2meta);
+ if (ret < 0) {
+ qemu_co_mutex_lock(&s->lock);
+ goto fail;
+ }
+
/* If we need to do COW, check if it's possible to merge the
* writing of the guest data together with that of the COW regions.
* If it's not possible (or not necessary) then write the
* guest data now. */
if (!merge_cow(offset, cur_bytes, &hd_qiov, l2meta)) {
- qemu_co_mutex_unlock(&s->lock);
BLKDBG_EVENT(bs->file, BLKDBG_WRITE_AIO);
trace_qcow2_writev_data(qemu_coroutine_self(),
cluster_offset + offset_in_cluster);
ret = bdrv_co_pwritev(s->data_file,
cluster_offset + offset_in_cluster,
cur_bytes, &hd_qiov, 0);
- qemu_co_mutex_lock(&s->lock);
if (ret < 0) {
+ qemu_co_mutex_lock(&s->lock);
goto fail;
}
}
+ qemu_co_mutex_lock(&s->lock);
+
ret = qcow2_handle_l2meta(bs, &l2meta, true);
if (ret) {
goto fail;
@@ -68,6 +68,7 @@ qcow2_writev_done_part(void *co, int cur_bytes) "co %p cur_bytes %d"
qcow2_writev_data(void *co, uint64_t offset) "co %p offset 0x%" PRIx64
qcow2_pwrite_zeroes_start_req(void *co, int64_t offset, int count) "co %p offset 0x%" PRIx64 " count %d"
qcow2_pwrite_zeroes(void *co, int64_t offset, int count) "co %p offset 0x%" PRIx64 " count %d"
+qcow2_skip_cow(void *co, uint64_t offset, int nb_clusters) "co %p offset 0x%" PRIx64 " nb_clusters %d"
# qcow2-cluster.c
qcow2_alloc_clusters_offset(void *co, uint64_t offset, int bytes) "co %p offset 0x%" PRIx64 " bytes %d"
@@ -150,10 +150,15 @@ $QEMU_IO -c "$OPEN_RO" -c "read -P 1 0 512" | _filter_qemu_io
echo
echo "=== Testing overlap while COW is in flight ==="
echo
+BACKING_IMG=$TEST_IMG.base
+TEST_IMG=$BACKING_IMG _make_test_img 1G
+
+$QEMU_IO -c 'write 0k 64k' "$BACKING_IMG" | _filter_qemu_io
+
# compat=0.10 is required in order to make the following discard actually
# unallocate the sector rather than make it a zero sector - we want COW, after
# all.
-IMGOPTS='compat=0.10' _make_test_img 1G
+IMGOPTS='compat=0.10' _make_test_img -b "$BACKING_IMG" 1G
# Write two clusters, the second one enforces creation of an L2 table after
# the first data cluster.
$QEMU_IO -c 'write 0k 64k' -c 'write 512M 64k' "$TEST_IMG" | _filter_qemu_io
@@ -97,7 +97,10 @@ read 512/512 bytes at offset 0
=== Testing overlap while COW is in flight ===
-Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=1073741824
+Formatting 'TEST_DIR/t.IMGFMT.base', fmt=IMGFMT size=1073741824
+wrote 65536/65536 bytes at offset 0
+64 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=1073741824 backing_file=TEST_DIR/t.IMGFMT.base
wrote 65536/65536 bytes at offset 0
64 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
wrote 65536/65536 bytes at offset 536870912
If COW areas of the newly allocated clusters are zeroes on the backing image, efficient bdrv_write_zeroes(flags=BDRV_REQ_NO_FALLBACK) can be used on the whole cluster instead of writing explicit zero buffers later in perform_cow(). iotest 060: write to the discarded cluster does not trigger COW anymore. Use a backing image instead. Signed-off-by: Anton Nefedov <anton.nefedov@virtuozzo.com> --- qapi/block-core.json | 4 +- block/qcow2.h | 6 +++ block/qcow2-cluster.c | 2 +- block/qcow2.c | 93 +++++++++++++++++++++++++++++++++++++- block/trace-events | 1 + tests/qemu-iotests/060 | 7 ++- tests/qemu-iotests/060.out | 5 +- 7 files changed, 112 insertions(+), 6 deletions(-)