If COW areas of the newly allocated clusters are zeroes on the backing image, efficient bdrv_write_zeroes(flags=BDRV_REQ_ALLOCATE) 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. iotest 066: cluster-alignment areas that were not really COWed are now detected as zeroes, hence the initial write has to be exactly the same size for the maps to match Signed-off-by: Anton Nefedov <anton.nefe...@virtuozzo.com> --- qapi/block-core.json | 4 ++- block/qcow2.h | 6 +++++ block/qcow2-cluster.c | 2 +- block/qcow2.c | 66 ++++++++++++++++++++++++++++++++++++++++++++-- block/trace-events | 1 + tests/qemu-iotests/060 | 26 +++++++++++------- tests/qemu-iotests/060.out | 5 +++- tests/qemu-iotests/066 | 2 +- tests/qemu-iotests/066.out | 4 +-- 9 files changed, 98 insertions(+), 18 deletions(-) diff --git a/qapi/block-core.json b/qapi/block-core.json index e94a688..1579a77 100644 --- a/qapi/block-core.json +++ b/qapi/block-core.json @@ -2546,6 +2546,8 @@ # # @cor_write: a write due to copy-on-read (since 2.11) # +# @cluster_alloc_space: an allocation of a cluster file space (since 2.12) +# # Since: 2.9 ## { 'enum': 'BlkdebugEvent', 'prefix': 'BLKDBG', @@ -2564,7 +2566,7 @@ '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: diff --git a/block/qcow2.h b/block/qcow2.h index 46c8cf4..e6e3a22 100644 --- a/block/qcow2.h +++ b/block/qcow2.h @@ -377,6 +377,12 @@ 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 * from @cow_start and @cow_end into one single write operation. diff --git a/block/qcow2-cluster.c b/block/qcow2-cluster.c index a3fec27..511ceb8 100644 --- a/block/qcow2-cluster.c +++ b/block/qcow2-cluster.c @@ -791,7 +791,7 @@ 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; } diff --git a/block/qcow2.c b/block/qcow2.c index 2ed21ff..087cb26 100644 --- a/block/qcow2.c +++ b/block/qcow2.c @@ -1833,6 +1833,11 @@ 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) { @@ -1875,6 +1880,52 @@ static bool is_zero(BlockDriverState *bs, int64_t offset, int64_t bytes) return res >= 0 && (res & BDRV_BLOCK_ZERO) && nr == bytes; } +static bool is_zero_cow(BlockDriverState *bs, QCowL2Meta *m) +{ + return is_zero(bs, m->offset + m->cow_start.offset, + m->cow_start.nb_bytes) && + is_zero(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; + + for (m = l2meta; m != NULL; m = m->next) { + int ret; + + if (!m->cow_start.nb_bytes && !m->cow_end.nb_bytes) { + continue; + } + + if (bs->encrypted) { + continue; + } + + if (!is_zero_cow(bs, m)) { + continue; + } + + BLKDBG_EVENT(bs->file, BLKDBG_CLUSTER_ALLOC_SPACE); + /* instead of writing zero COW buffers, + efficiently zero out the whole clusters */ + ret = bdrv_co_pwrite_zeroes(bs->file, m->alloc_offset, + m->nb_clusters * s->cluster_size, + BDRV_REQ_ALLOCATE); + 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) @@ -1957,24 +2008,35 @@ static coroutine_fn int qcow2_co_pwritev(BlockDriverState *bs, uint64_t offset, goto fail; } + qemu_co_mutex_unlock(&s->lock); + + if (bs->file->bs->supported_zero_flags & BDRV_REQ_ALLOCATE) { + 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(bs->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); + while (l2meta != NULL) { QCowL2Meta *next; diff --git a/block/trace-events b/block/trace-events index 11c8d5f..c9fa596 100644 --- a/block/trace-events +++ b/block/trace-events @@ -61,6 +61,7 @@ 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" # block/qcow2-cluster.c qcow2_alloc_clusters_offset(void *co, uint64_t offset, int bytes) "co %p offset 0x%" PRIx64 " bytes %d" diff --git a/tests/qemu-iotests/060 b/tests/qemu-iotests/060 index 14797dd..92beff4 100755 --- a/tests/qemu-iotests/060 +++ b/tests/qemu-iotests/060 @@ -143,27 +143,33 @@ $QEMU_IO -c "$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 + +$QEMU_IO -c 'write 64k 64k' "$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 +# unallocate the sector rather than make it a zero sector as we would like +# to reuse it for another guest offset +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 -# Discard the first cluster. This cluster will soon enough be reallocated and -# used for COW. +# Discard the first cluster. This cluster will soon enough be reallocated $QEMU_IO -c 'discard 0k 64k' "$TEST_IMG" | _filter_qemu_io # Now, corrupt the image by marking the second L2 table cluster as free. poke_file "$TEST_IMG" '131084' "\x00\x00" # 0x2000c -# Start a write operation requiring COW on the image stopping it right before -# doing the read; then, trigger the corruption prevention by writing anything to -# any unallocated cluster, leading to an attempt to overwrite the second L2 +# Start a write operation requiring COW on the image; +# this write will reuse the host offset released by a previous discard. +# Stop it right before doing the read. +# Then, trigger the corruption prevention by writing anything to +# another unallocated cluster, leading to an attempt to overwrite the second L2 # table. Finally, resume the COW write and see it fail (but not crash). echo "open -o file.driver=blkdebug $TEST_IMG break cow_read 0 -aio_write 0k 1k +aio_write 64k 1k wait_break 0 -write 64k 64k +write 128k 64k resume 0" | $QEMU_IO | _filter_qemu_io echo diff --git a/tests/qemu-iotests/060.out b/tests/qemu-iotests/060.out index c4cb7c6..15d95d5 100644 --- a/tests/qemu-iotests/060.out +++ b/tests/qemu-iotests/060.out @@ -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 65536 +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 diff --git a/tests/qemu-iotests/066 b/tests/qemu-iotests/066 index 8638217..3c216a1 100755 --- a/tests/qemu-iotests/066 +++ b/tests/qemu-iotests/066 @@ -71,7 +71,7 @@ echo _make_test_img $IMG_SIZE # Create data clusters (not aligned to an L2 table) -$QEMU_IO -c 'write -P 42 1M 256k' "$TEST_IMG" | _filter_qemu_io +$QEMU_IO -c "write -P 42 $(((1024 + 32) * 1024)) 192k" "$TEST_IMG" | _filter_qemu_io orig_map=$($QEMU_IMG map --output=json "$TEST_IMG") # Convert the data clusters to preallocated zero clusters diff --git a/tests/qemu-iotests/066.out b/tests/qemu-iotests/066.out index 3d9da9b..093431e 100644 --- a/tests/qemu-iotests/066.out +++ b/tests/qemu-iotests/066.out @@ -19,8 +19,8 @@ Offset Length Mapped to File === Writing to preallocated zero clusters === Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=67109376 -wrote 262144/262144 bytes at offset 1048576 -256 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec) +wrote 196608/196608 bytes at offset 1081344 +192 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec) wrote 262144/262144 bytes at offset 1048576 256 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec) wrote 196608/196608 bytes at offset 1081344 -- 2.7.4