On Thu, Apr 20, 2017 at 4:38 PM, <jemmy858...@gmail.com> wrote:
> From: Lidong Chen <lidongc...@tencent.com>
>
> when the buffer is zero, blk_co_pwrite_zeroes is more effectively than
> blk_co_pwritev with BDRV_REQ_WRITE_COMPRESSED. this patch can reduces
> the time when converts the qcow2 image with lots of zero.
>
the original qcow2 file which have lots of cluster unallocated:
[root]# qemu-img info /mnt/img2016111016860868_old.qcow2
image: /mnt/img2016111016860868_old.qcow2
file format: qcow2
virtual size: 20G (21474836480 bytes)
disk size: 214M (224460800 bytes)
cluster_size: 65536
backing file: /baseimage/img2015122818606660/img2015122818606660.qcow2
the time used for qemu-img convert:
[root ~]# time /root/kvm/bin/qemu-img convert -c -p -o
backing_file=/baseimage/img2015122818606660/img2015122818606660.qcow2
-O
qcow2 /mnt/img2016111016860868.qcow2 /mnt/img2016111016860868_old.qcow2
(100.00/100%)
real 0m29.456s
user 0m29.345s
sys 0m0.481s
run dd if=/dev/zero of=./test bs=65536 in guest os
then convert again.
before apply this patch:
[root~]# time /root/kvm/bin/qemu-img convert -c -p -o
backing_file=/baseimage/img2015122818606660/img2015122818606660.qcow2
-O qcow2 /mnt/img2016111016860868.qcow2 /mnt/img2016111016860868_new.qcow2
(100.00/100%)
real 5m35.617s
user 5m33.417s
sys 0m10.699s
after apply this patch:
[root~]# time /root/kvm/bin/qemu-img convert -c -p -o
backing_file=/baseimage/img2015122818606660/img2015122818606660.qcow2
-O
qcow2 /mnt/img2016111016860868.qcow2 /mnt/img2016111016860868_new1.qcow2
(100.00/100%)
real 0m51.189s
user 0m35.239s
sys 0m14.251s
the time reduce from 5m35.617s to 0m51.189s.
[root ]# ll /mnt/img2016111016860868* -h
-rw-r--r-- 1 root root 254M Apr 20 14:50 /mnt/img2016111016860868_new.qcow2
-rw-r--r-- 1 root root 232M Apr 20 15:27 /mnt/img2016111016860868_new1.qcow2
the size reduce from 254M to 232M.
> Signed-off-by: Lidong Chen <lidongc...@tencent.com>
> ---
> qemu-img.c | 19 +++++++++++++------
> 1 file changed, 13 insertions(+), 6 deletions(-)
>
> diff --git a/qemu-img.c b/qemu-img.c
> index b220cf7..0256539 100644
> --- a/qemu-img.c
> +++ b/qemu-img.c
> @@ -1675,13 +1675,20 @@ static int coroutine_fn
> convert_co_write(ImgConvertState *s, int64_t sector_num,
> * write if the buffer is completely zeroed and we're allowed to
> * keep the target sparse. */
> if (s->compressed) {
> - if (s->has_zero_init && s->min_sparse &&
> - buffer_is_zero(buf, n * BDRV_SECTOR_SIZE))
> - {
> - assert(!s->target_has_backing);
> - break;
> + if (buffer_is_zero(buf, n * BDRV_SECTOR_SIZE)) {
> + if (s->has_zero_init && s->min_sparse) {
> + assert(!s->target_has_backing);
> + break;
> + } else {
> + ret = blk_co_pwrite_zeroes(s->target,
> + sector_num << BDRV_SECTOR_BITS,
> + n << BDRV_SECTOR_BITS, 0);
> + if (ret < 0) {
> + return ret;
> + }
> + break;
> + }
> }
> -
> iov.iov_base = buf;
> iov.iov_len = n << BDRV_SECTOR_BITS;
> qemu_iovec_init_external(&qiov, &iov, 1);
> --
> 1.8.3.1
>
