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

[Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>]

20.01.2020 16:58, Max Reitz wrote:
> 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):


I agree)

> 
> 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;
>>       }
>>   }
>>   
>>
> 


-- 
Best regards,
Vladimir