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Re: [Qemu-block] [PATCH v7 04/10] block: Support meta dirty bitmap


From: John Snow
Subject: Re: [Qemu-block] [PATCH v7 04/10] block: Support meta dirty bitmap
Date: Fri, 22 Jul 2016 17:58:45 -0400
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.1.1


On 07/22/2016 05:57 PM, Max Reitz wrote:
> On 18.07.2016 22:57, 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(+)
> 
> [...]
> 
>> +int bdrv_dirty_bitmap_get_meta(BlockDriverState *bs,
>> +                               BdrvDirtyBitmap *bitmap, int64_t sector,
>> +                               int nb_sectors)
>> +{
>> +    uint64_t i;
>> +    int gran = hbitmap_granularity(bitmap->meta);
> 
> /me is making a note first: If John says an optimization may be
> premature, it probably is.
> 
> Did I say hbitmap_granularity()? I may have wanted to actually say
> "1 << hbitmap_granularity()". Sorry. :-/
> 
> /me is making a second note now: Look up how something works before
> proposing it, not after someone has actually followed your advice.
> 
> Max
> 

Haha, alright. I will ACTUALLY sit down and make this nice tonight.

I'll have to turn off autopilot for a few bleeding moments.

--js

>> +
>> +    /* To optimize: we can make hbitmap to internally check the range in a
>> +     * coarse level, or at least do it word by word. */
>> +    for (i = sector; i < sector + nb_sectors; i += gran) {
>> +        if (hbitmap_get(bitmap->meta, i)) {
>> +            return true;
>> +        }
>> +    }
>> +    return false;
>> +}
> 



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