Re: [PATCH 0/6] reiser4: discard support: "precise discard" aka padding of extents to erase unit boundaries.

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

On 12/15/2014 08:30 PM, Edward Shishkin wrote:
> On 12/14/2014 09:03 AM, Ivan Shapovalov wrote:
>> On Saturday 13 December 2014 at 23:38:02, Edward Shishkin wrote:
>>> On 12/12/2014 10:10 PM, Ivan Shapovalov wrote:
>>>> So, this patchset uses your algorithm of padding/gluing extents to 
>>>> be discarded.
>>>> I've added exact allocation primitives (is it what you've been 
>>>> talking about?
>>>
>>> So, we found out that the old bitmap primitives don't allow us to 
>>> implement
>>> precise discard, and I asked for new ones. Also we wanted to 
>>> implement the
>>> general case, when precise discard works for any pair (offset, unit).
>>> Currently
>>> it works only for ones determined by the function 
>>> convert_lattice_params().
>>> For some reasons (that I don't remember) I was sure, that the 
>>> general case
>>> should be obtained from this partial case by a small transformation 
>>> of the
>>> function discard_sorted_merged_extents().
>>>
>>> Well, I'll try to dive into details and generalize things on the 
>>> holidays.
>>> If generalization is impossible, 


Hopefully this is possible,
I'll try to send the patch in short.

Edward.


>>> then we'll switch to non-precise
>>> discard every
>>> time when convert_lattice_params() fails.
>> I don't quite understand you here... Do you mean that some non-insane 
>> combinations
>> of discard unit, discard offset and blocksize are not handled (but worth
>> handling)?
>
>
> Yes. As you can see, if (discard_offset % block_size != 0), then we
> don't issue discard requests. Neither precise, nor non-precise.
> It is hard to implement the precise discard support in the generic 
> case straight away.
>
>
>>
>> TBH, convert_lattice_params() looks magic-ish to me...
>
>
> OK, I'll try to provide some background (geometric minimum).
>
> Edward.