Re: [PATCH v2 2/7] block/block-copy: use block_status

[Max Reitz]

On 27.11.19 19:08, Vladimir Sementsov-Ogievskiy wrote:
> Use bdrv_block_status_above to chose effective chunk size and to handle
> zeroes effectively.
> 
> This substitutes checking for just being allocated or not, and drops
> old code path for it. Assistance by backup job is dropped too, as
> caching block-status information is more difficult than just caching
> is-allocated information in our dirty bitmap, and backup job is not
> good place for this caching anyway.
> 
> Signed-off-by: Vladimir Sementsov-Ogievskiy <address@hidden>
> ---
>  block/block-copy.c | 67 +++++++++++++++++++++++++++++++++++++---------
>  block/trace-events |  1 +
>  2 files changed, 55 insertions(+), 13 deletions(-)
> 
> diff --git a/block/block-copy.c b/block/block-copy.c
> index 8602e2cae7..74295d93d5 100644
> --- a/block/block-copy.c
> +++ b/block/block-copy.c

[...]

> @@ -336,23 +375,25 @@ int coroutine_fn block_copy(BlockCopyState *s,
>              chunk_end = next_zero;
>          }
>  
> -        if (s->skip_unallocated) {
> -            ret = block_copy_reset_unallocated(s, start, &status_bytes);
> -            if (ret == 0) {
> -                trace_block_copy_skip_range(s, start, status_bytes);
> -                start += status_bytes;
> -                continue;
> -            }
> -            /* Clamp to known allocated region */
> -            chunk_end = MIN(chunk_end, start + status_bytes);
> +        ret = block_copy_block_status(s, start, chunk_end - start,
> +                                      &status_bytes);
> +        if (s->skip_unallocated && !(ret & BDRV_BLOCK_ALLOCATED)) {
> +            bdrv_reset_dirty_bitmap(s->copy_bitmap, start, status_bytes);
> +            s->progress_reset_callback(s->progress_opaque);
> +            trace_block_copy_skip_range(s, start, status_bytes);
> +            start += status_bytes;
> +            continue;
>          }
>  
> +        chunk_end = MIN(chunk_end, start + status_bytes);

I’m not sure how much the old “Clamp to known allocated region” actually
helps, but I wouldn’t drop it anyway.

Apart from this nit, the patch looks good to me.

Max

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