Re: [Qemu-block] [PATCH v2 6/7] mirror: efficiently zero out target

[John Snow]

On 07/07/2016 05:35 AM, Denis V. Lunev wrote:
> With a bdrv_co_write_zeroes method on a target BDS zeroes will not be placed
> into the wire. Thus the target could be very efficiently zeroed out. This
> is should be done with the largest chunk possible.
> 
> Signed-off-by: Denis V. Lunev <address@hidden>
> Reviewed-by: Vladimir Sementsov-Ogievskiy<address@hidden>
> CC: Stefan Hajnoczi <address@hidden>
> CC: Fam Zheng <address@hidden>
> CC: Kevin Wolf <address@hidden>
> CC: Max Reitz <address@hidden>
> CC: Jeff Cody <address@hidden>
> CC: Eric Blake <address@hidden>
> ---
>  block/mirror.c | 33 +++++++++++++++++++++++++++++++--
>  1 file changed, 31 insertions(+), 2 deletions(-)
> 
> diff --git a/block/mirror.c b/block/mirror.c
> index 7208023..4ecfbf1 100644
> --- a/block/mirror.c
> +++ b/block/mirror.c
> @@ -526,8 +526,37 @@ static int mirror_dirty_init(MirrorBlockJob *s)
>      last_pause_ns = qemu_clock_get_ns(QEMU_CLOCK_REALTIME);
>  
>      if (base == NULL && !bdrv_has_zero_init(target_bs)) {
> -        bdrv_set_dirty_bitmap(s->dirty_bitmap, 0, end);
> -        return 0;
> +        if (!bdrv_can_write_zeroes_with_unmap(target_bs)) {
> +            bdrv_set_dirty_bitmap(s->dirty_bitmap, 0, end);
> +            return 0;
> +        }
> +
> +        for (sector_num = 0; sector_num < end; ) {
> +            int64_t now = qemu_clock_get_ns(QEMU_CLOCK_REALTIME);
> +
> +            int nb_sectors = QEMU_ALIGN_DOWN(INT_MAX, s->granularity);
> +            nb_sectors = MIN(nb_sectors >> BDRV_SECTOR_BITS, end - 
> sector_num);
> +
> +            if (now - last_pause_ns > SLICE_TIME) {
> +                last_pause_ns = now;
> +                block_job_sleep_ns(&s->common, QEMU_CLOCK_REALTIME, 0);
> +            }
> +
> +            if (block_job_is_cancelled(&s->common)) {
> +                return 0;
> +            }
> +
> +            if (s->in_flight >= MAX_IN_FLIGHT) {
> +                trace_mirror_yield(s, s->in_flight, s->buf_free_count, -1);
> +                mirror_wait_for_io(s);
> +                continue;
> +            }
> +
> +            mirror_do_zero_or_discard(s, sector_num, nb_sectors, false);
> +            sector_num += nb_sectors;
> +        }
> +
> +        mirror_drain(s);
>      }
>  
>      /* First part, loop on the sectors and initialize the dirty bitmap.  */
> 

Apart from needing the coroutine tag and Eric's comments, I think this
is fine.

--js