| Message ID | 1509551048-129830-9-git-send-email-anton.nefedov@virtuozzo.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Wed 01 Nov 2017 04:44:01 PM CET, Anton Nefedov wrote: > 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. > so, break on write_aio event instead, will work for the test > (but write won't fail anymore, so update reference output) > > 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.nefedov@virtuozzo.com> > --- > block/qcow2.h | 6 +++++ > block/qcow2-cluster.c | 3 ++- > block/qcow2.c | 67 ++++++++++++++++++++++++++++++++++++++++++++-- > block/trace-events | 1 + > tests/qemu-iotests/060 | 2 +- > tests/qemu-iotests/060.out | 3 ++- > tests/qemu-iotests/066 | 2 +- > tests/qemu-iotests/066.out | 4 +-- > 8 files changed, 80 insertions(+), 8 deletions(-) > > diff --git a/block/qcow2.h b/block/qcow2.h > index 782a206..e312e48 100644 > --- a/block/qcow2.h > +++ b/block/qcow2.h > @@ -377,6 +377,12 @@ typedef struct QCowL2Meta > Qcow2COWRegion cow_end; > > /** > + * Indicates that both COW areas are empty (nb_bytes == 0) > + * or filled with zeroes and do not require any more copying > + */ > + bool zero_cow; I think the terminology elsewhere is "COW regions". Also, in this patch that field doesn't really seem to track the case where both regions have nb_bytes == 0, or does it? It seems to be checked separately in all cases. Example: > - if (start->nb_bytes == 0 && end->nb_bytes == 0) { > + if ((start->nb_bytes == 0 && end->nb_bytes == 0) || m->zero_cow) { > return 0; > } Here, 'if (m->zero_cow)' would suffice. > + /* If both COW regions are zeroes already, skip this too */ > + if (m->zero_cow) { > + continue; > + } Same as above > +static bool is_zero_cow(BlockDriverState *bs, QCowL2Meta *m) > +{ > + if (bs->encrypted) { > + return false; > + } > + > + if (m->cow_start.nb_bytes != 0 && > + !is_zero(bs, m->offset + m->cow_start.offset, m->cow_start.nb_bytes)) > + { > + return false; > + } > + > + if (m->cow_end.nb_bytes != 0 && > + !is_zero(bs, m->offset + m->cow_end.offset, m->cow_end.nb_bytes)) > + { > + return false; > + } Why do you need to check that nb_bytes != 0? Doesn't is_zero() do that already? Berto
On 15/1/2018 6:31 PM, Alberto Garcia wrote: > On Wed 01 Nov 2017 04:44:01 PM CET, Anton Nefedov wrote: >> 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. >> so, break on write_aio event instead, will work for the test >> (but write won't fail anymore, so update reference output) >> >> 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.nefedov@virtuozzo.com> >> --- >> block/qcow2.h | 6 +++++ >> block/qcow2-cluster.c | 3 ++- >> block/qcow2.c | 67 ++++++++++++++++++++++++++++++++++++++++++++-- >> block/trace-events | 1 + >> tests/qemu-iotests/060 | 2 +- >> tests/qemu-iotests/060.out | 3 ++- >> tests/qemu-iotests/066 | 2 +- >> tests/qemu-iotests/066.out | 4 +-- >> 8 files changed, 80 insertions(+), 8 deletions(-) >> >> diff --git a/block/qcow2.h b/block/qcow2.h >> index 782a206..e312e48 100644 >> --- a/block/qcow2.h >> +++ b/block/qcow2.h >> @@ -377,6 +377,12 @@ typedef struct QCowL2Meta >> Qcow2COWRegion cow_end; >> >> /** >> + * Indicates that both COW areas are empty (nb_bytes == 0) >> + * or filled with zeroes and do not require any more copying >> + */ >> + bool zero_cow; > > I think the terminology elsewhere is "COW regions". > Hi Berto! thanks much for checking this series Will fix 'areas' to 'regions' > Also, in this patch that field doesn't really seem to track the case > where both regions have nb_bytes == 0, or does it? It seems to be > checked separately in all cases. > > Example: > >> - if (start->nb_bytes == 0 && end->nb_bytes == 0) { >> + if ((start->nb_bytes == 0 && end->nb_bytes == 0) || m->zero_cow) { >> return 0; >> } > > Here, 'if (m->zero_cow)' would suffice. > The thing is, zero_cow is not assigned on some code paths, e.g. !(bs->file->bs->supported_zero_flags & BDRV_REQ_ALLOCATE) or when bs->encrypted. but now thinking about this again; probably it should be - that will be least confusing. I'll fix >> + /* If both COW regions are zeroes already, skip this too */ >> + if (m->zero_cow) { >> + continue; >> + } > > Same as above > Yep. >> +static bool is_zero_cow(BlockDriverState *bs, QCowL2Meta *m) >> +{ >> + if (bs->encrypted) { >> + return false; >> + } >> + >> + if (m->cow_start.nb_bytes != 0 && >> + !is_zero(bs, m->offset + m->cow_start.offset, m->cow_start.nb_bytes)) >> + { >> + return false; >> + } >> + >> + if (m->cow_end.nb_bytes != 0 && >> + !is_zero(bs, m->offset + m->cow_end.offset, m->cow_end.nb_bytes)) >> + { >> + return false; >> + } > > Why do you need to check that nb_bytes != 0? Doesn't is_zero() do that > already? > I really don't; I think previously is_zero() didn't have that check and I didn't notice it introduced during a rebase. Will fix > Berto >
On Mon 15 Jan 2018 07:21:01 PM CET, Anton Nefedov wrote: >>> /** >>> + * Indicates that both COW areas are empty (nb_bytes == 0) >>> + * or filled with zeroes and do not require any more copying >>> + */ >>> + bool zero_cow; [...] >>> - if (start->nb_bytes == 0 && end->nb_bytes == 0) { >>> + if ((start->nb_bytes == 0 && end->nb_bytes == 0) || m->zero_cow) { >>> return 0; >>> } >> >> Here, 'if (m->zero_cow)' would suffice. > > The thing is, zero_cow is not assigned on some code paths, > e.g. !(bs->file->bs->supported_zero_flags & BDRV_REQ_ALLOCATE) > or when bs->encrypted. Right, that's why I said that the comment on the zero_cow field is incorrect, zero_cow does not indicate when nb_bytes == 0. > but now thinking about this again; probably it should be - that will > be least confusing. I'll fix Choose the simplest solution, as long as the documentation matches the semantics. Berto
diff --git a/block/qcow2.h b/block/qcow2.h index 782a206..e312e48 100644 --- a/block/qcow2.h +++ b/block/qcow2.h @@ -377,6 +377,12 @@ typedef struct QCowL2Meta Qcow2COWRegion cow_end; /** + * Indicates that both COW areas are empty (nb_bytes == 0) + * or filled with zeroes and do not require any more copying + */ + bool zero_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 fb10e26..e364116 100644 --- a/block/qcow2-cluster.c +++ b/block/qcow2-cluster.c @@ -783,7 +783,7 @@ 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->zero_cow) { return 0; } @@ -1383,6 +1383,7 @@ static int handle_alloc(BlockDriverState *bs, uint64_t guest_offset, .offset = nb_bytes, .nb_bytes = avail_bytes - nb_bytes, }, + .zero_cow = false, }; qemu_co_queue_init(&(*m)->dependent_requests); QLIST_INSERT_HEAD(&s->cluster_allocs, *m, next_in_flight); diff --git a/block/qcow2.c b/block/qcow2.c index db759ce..827058d 100644 --- a/block/qcow2.c +++ b/block/qcow2.c @@ -1856,6 +1856,11 @@ static bool merge_cow(uint64_t offset, unsigned bytes, continue; } + /* If both COW regions are zeroes already, skip this too */ + if (m->zero_cow) { + continue; + } + /* The data (middle) region must be immediately after the * start region */ if (l2meta_cow_start(m) + m->cow_start.nb_bytes != offset) { @@ -1898,6 +1903,57 @@ 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) +{ + if (bs->encrypted) { + return false; + } + + if (m->cow_start.nb_bytes != 0 && + !is_zero(bs, m->offset + m->cow_start.offset, m->cow_start.nb_bytes)) + { + return false; + } + + if (m->cow_end.nb_bytes != 0 && + !is_zero(bs, m->offset + m->cow_end.offset, m->cow_end.nb_bytes)) + { + return false; + } + + return true; +} + +static void 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 (!is_zero_cow(bs, m)) { + continue; + } + + /* 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) { + continue; + } + + trace_qcow2_skip_cow(qemu_coroutine_self(), m->offset, m->nb_clusters); + m->zero_cow = true; + } +} + static coroutine_fn int qcow2_co_pwritev(BlockDriverState *bs, uint64_t offset, uint64_t bytes, QEMUIOVector *qiov, int flags) @@ -1980,24 +2036,31 @@ 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) { + handle_alloc_space(bs, l2meta); + } + /* 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 8e95c45..3a0f096 100755 --- a/tests/qemu-iotests/060 +++ b/tests/qemu-iotests/060 @@ -160,7 +160,7 @@ poke_file "$TEST_IMG" '131084' "\x00\x00" # 0x2000c # any 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 +break write_aio 0 aio_write 0k 1k wait_break 0 write 64k 64k diff --git a/tests/qemu-iotests/060.out b/tests/qemu-iotests/060.out index 5ca3af4..736dc30 100644 --- a/tests/qemu-iotests/060.out +++ b/tests/qemu-iotests/060.out @@ -108,7 +108,8 @@ qcow2: Marking image as corrupt: Preventing invalid write on metadata (overlaps blkdebug: Suspended request '0' write failed: Input/output error blkdebug: Resuming request '0' -aio_write failed: No medium found +wrote 1024/1024 bytes at offset 0 +1 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec) === Testing unallocated image header === 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
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. so, break on write_aio event instead, will work for the test (but write won't fail anymore, so update reference output) 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.nefedov@virtuozzo.com> --- block/qcow2.h | 6 +++++ block/qcow2-cluster.c | 3 ++- block/qcow2.c | 67 ++++++++++++++++++++++++++++++++++++++++++++-- block/trace-events | 1 + tests/qemu-iotests/060 | 2 +- tests/qemu-iotests/060.out | 3 ++- tests/qemu-iotests/066 | 2 +- tests/qemu-iotests/066.out | 4 +-- 8 files changed, 80 insertions(+), 8 deletions(-)