Re: reiser4: discard implementation, pass 2: allocation issues

[Edward Shishkin <edward.shishkin@gmail.com>]

On 06/17/2014 12:14 PM, Ivan Shapovalov wrote:
> On Tuesday 17 June 2014 at 02:37:16, Edward Shishkin wrote:	
>> [...]
>>
>> Yup, blocknr sets minimize memory consumption and are unsortable...
>>
>> I think that the cleanest option will be using lists (instead of blocknr
>> sets) for
>> the delete sets, if the discard is turned on. It will reduce memory
>> consumption
>> by 20%. Indeed, every entry in a blocknr_set occupies ~8 bytes (assuming
>> that everything is pretty fragmented because of txmod=wa), whereas a list
>> entry occupies 32 bytes (start, length, plus 2 pointers for the link).
>>
>> In this option we'll need to join lists (instead of merging blocknr
>> sets) during
>> atoms fusion and apply the list (instead of blocknr set) to the COMMIT
>> BITMAP
>> at pre_commit_hook(). I think it won't be a problem, since the lists are
>> simpler
>> than blocknr sets.
> That's a neat approach. I think I'll use unions and do the decision at runtime.


Yup.
So, if discard is on, we work with 2 lists (delete_set, 
delete_set_for_wander).
If discard is off, we work with one blocknr set..