Re: [Qemu-devel] [PATCH v6 04/10] block: Support meta dirty bitmap

[John Snow]

On 07/18/2016 10:57 AM, Max Reitz wrote:
> On 15.07.2016 22:27, John Snow wrote:
>> From: Fam Zheng <address@hidden>
>>
>> The added group of operations enables tracking of the changed bits in
>> the dirty bitmap.
>>
>> Signed-off-by: Fam Zheng <address@hidden>
>> Reviewed-by: Max Reitz <address@hidden>
>> Signed-off-by: John Snow <address@hidden>
>> ---
>>  block/dirty-bitmap.c         | 52 
>> ++++++++++++++++++++++++++++++++++++++++++++
>>  include/block/dirty-bitmap.h |  9 ++++++++
>>  2 files changed, 61 insertions(+)
>>
>> diff --git a/block/dirty-bitmap.c b/block/dirty-bitmap.c
>> index 628b77c..9c53c56 100644
>> --- a/block/dirty-bitmap.c
>> +++ b/block/dirty-bitmap.c
>> @@ -38,6 +38,7 @@
> 
> [...]
> 
>> +int bdrv_dirty_bitmap_get_meta(BlockDriverState *bs,
>> +                               BdrvDirtyBitmap *bitmap, int64_t sector,
>> +                               int nb_sectors)
>> +{
>> +    uint64_t i;
>> +    int gran = bdrv_dirty_bitmap_granularity(bitmap) >> BDRV_SECTOR_BITS;
>> +
>> +    /* To optimize: we can make hbitmap to internally check the range in a
>> +     * coarse level, or at least do it word by word. */
> 
> So you really want to leave even the simple optimizations for later? :-)
> 

I guess partly I felt bad about not going all the way on it, but I can
bring it a little closer :)

> (i.e. "int gran = hbitmap_granularity(bitmap->meta);")
> 
> Max
> 
>> +    for (i = sector; i < sector + nb_sectors; i += gran) {
>> +        if (hbitmap_get(bitmap->meta, i)) {
>> +            return true;
>> +        }
>> +    }
>> +    return false;
>> +}
> 
>