Re: reiser4: discard support

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

On 05/03/2014 10:32 PM, Ivan Shapovalov wrote:
> On Saturday 03 May 2014 at 22:21:58, Edward Shishkin wrote:	
>
> TBH, I have never looked at the deallocation paths in reiser4: everything
> worked fine there.. BTW, why not to use atom's delete_set to discard
> things? Could you please take a look?
[...]
>>> Blocks used for the journal (wander.c) are deallocated without BA_DEFER
>>> set
>>> and thus they never hit delete_set. However, we want to discard these.
>> This happens in error paths. Don't be so scrupulous ;)
> I don't think so:
> - wander.c:485
>    dealloc_tx_list() <- reiser4_write_logs()
> - wander.c:505
>    dealloc_wmap_actor() <- dealloc_wmap() <- reiser4_write_logs()


Yep, indeed.
I don't completely understand this special case of wandered blocks.
Also I don't see where wandered blocks are deallocated after journal
replay (as journal is not needed any more): it can be a possible leak
of disk space after system crashes..
Once we understand it, I think we'll able to re-use the delete_set for
discard needs.

Edward.


>
>> Also users will use copy-on-write transaction model for their SSDs(*),
>> and in this mode journals are tiny: they contain only system blocks.
>> In short, there is nothing to discard..
>>
>> (*) http://marc.info/?l=reiserfs-devel&m=139449965000686&w=2
>>