Re: [PATCH v3 07/10] block/dirty-bitmap: improve _next_dirty_area API

[Max Reitz <mreitz@redhat.com>]

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On 19.12.19 11:03, Vladimir Sementsov-Ogievskiy wrote:
> Firstly, _next_dirty_area is for scenarios when we may contiguously
> search for next dirty area inside some limited region, so it is more
> comfortable to specify "end" which should not be recalculated on each
> iteration.
> 
> Secondly, let's add a possibility to limit resulting area size, not
> limiting searching area. This will be used in NBD code in further
> commit. (Note that now bdrv_dirty_bitmap_next_dirty_area is unused)
> 
> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
> ---
>  include/block/dirty-bitmap.h |  3 ++-
>  include/qemu/hbitmap.h       | 25 ++++++++++++---------
>  block/dirty-bitmap.c         |  6 +++--
>  tests/test-hbitmap.c         | 43 +++++++++++++++++++++++-------------
>  util/hbitmap.c               | 41 +++++++++++++++++++++-------------
>  5 files changed, 74 insertions(+), 44 deletions(-)

[...]

>  /**
> diff --git a/tests/test-hbitmap.c b/tests/test-hbitmap.c
> index e3f1b3f361..d75e84a76a 100644
> --- a/tests/test-hbitmap.c
> +++ b/tests/test-hbitmap.c
> @@ -920,18 +920,19 @@ static void test_hbitmap_next_x_after_truncate(TestHBitmapData *data,
>      test_hbitmap_next_x_check(data, 0);
>  }
>  
> -static void test_hbitmap_next_dirty_area_check(TestHBitmapData *data,
> -                                               int64_t offset,
> -                                               int64_t count)
> +static void test_hbitmap_next_dirty_area_check_limited(TestHBitmapData *data,
> +                                                       int64_t offset,
> +                                                       int64_t count,
> +                                                       int64_t max_dirty)
>  {
>      int64_t off1, off2;
>      int64_t len1 = 0, len2;
>      bool ret1, ret2;
>      int64_t end;
>  
> -    off1 = offset;
> -    len1 = count;
> -    ret1 = hbitmap_next_dirty_area(data->hb, &off1, &len1);
> +    ret1 = hbitmap_next_dirty_area(data->hb,
> +            offset, count == INT64_MAX ? INT64_MAX : offset + count, max_dirty,
> +            &off1, &len1);
>  
>      end = offset > data->size || data->size - offset < count ? data->size :
>                                                                 offset + count;
> @@ -940,21 +941,25 @@ static void test_hbitmap_next_dirty_area_check(TestHBitmapData *data,
>          ;

These empty statements look a bit weird to me.  But they’re
pre-existing, obviously.

>      }
>  
> -    for (len2 = 1; off2 + len2 < end && hbitmap_get(data->hb, off2 + len2);
> -         len2++) {
> +    for (len2 = 1; (off2 + len2 < end && len2 < max_dirty &&
> +                    hbitmap_get(data->hb, off2 + len2)); len2++)
> +    {
>          ;
>      }

[...]

> diff --git a/util/hbitmap.c b/util/hbitmap.c
> index d23f4b9678..2a1661ec1d 100644
> --- a/util/hbitmap.c
> +++ b/util/hbitmap.c
> @@ -270,22 +270,34 @@ int64_t hbitmap_next_zero(const HBitmap *hb, int64_t start, int64_t count)
>      return res;
>  }
>  
> -bool hbitmap_next_dirty_area(const HBitmap *hb, int64_t *start, int64_t *count)
> +bool hbitmap_next_dirty_area(const HBitmap *hb, int64_t start, int64_t end,
> +                             int64_t max_dirty_count,
> +                             int64_t *dirty_start, int64_t *dirty_count)
>  {
> -    int64_t area_start, area_end;
> +    int64_t next_zero;
>  
> -    area_start = hbitmap_next_dirty(hb, *start, *count);
> -    if (area_start < 0) {
> +    assert(start >= 0 && end >= 0 && max_dirty_count > 0);
> +
> +    if (start >= hb->orig_size || end <= start) {
> +        return false;
> +    }
> +
> +    end = MIN(end, hb->orig_size);

You could put this assignment before the if () and then drop the “start”
check from the condition.  (But that’s mostly me itching to do
optimizations.  I don’t think it’d make the code easier to read.)

[...]

> @@ -844,13 +856,12 @@ static void hbitmap_sparse_merge(HBitmap *dst, const HBitmap *src)
>      int64_t offset = 0;
>      int64_t count = src->orig_size;

These initializations are now unnecessary.  I’d drop them because I find
at least the one for @count a tiny bit confusing now.  (Because as a
reader, I’d wonder where this value is used.)

With that done (or maybe not because you disagree):

Reviewed-by: Max Reitz <mreitz@redhat.com>

>  
> -    while (hbitmap_next_dirty_area(src, &offset, &count)) {
> +    for (offset = 0;
> +         hbitmap_next_dirty_area(src, offset, src->orig_size, INT64_MAX,
> +                                 &offset, &count);
> +         offset += count)
> +    {
>          hbitmap_set(dst, offset, count);
> -        offset += count;
> -        if (offset >= src->orig_size) {
> -            break;
> -        }
> -        count = src->orig_size - offset;
>      }
>  }
>  
> 


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