Re: [PATCH v2 0/5] nilfs-utils: skip inefficient gc operations

[Andreas Rohner <andreas.rohner-hi6Y0CQ0nG0@public.gmane.org>]

On 2014-01-26 07:57, Ryusuke Konishi wrote:
> On Sat, 25 Jan 2014 19:33:42 +0300, Vyacheslav Dubeyko wrote:
>>
>> On Jan 24, 2014, at 5:18 PM, Andreas Rohner wrote:
>>
>>>>> You have to move the live blocks to a new segment, so you gain only (8
>>>>> MB - live_blocks) of free space.
>>>>
>>>> You always will have 8 MB after cleaning (garbage collection).  So, all segments
>>>> are identical from the free space point of view. What does GC check? And how
>>>> can GC distinguish segments on the basis of free space? All cleaned segments
>>>> return 8 MB free space for further allocation. So, all used segments will be over
>>>> any threshold.
>>>
>>> I am sorry if I wasn't clear enough. The invalidated blocks in a segment
>>> are basically unusable free space, that needs to be garbage collected.
>>> If you clean a segment you only gain the space of the invalidated
>>> blocks, from the perspective of the whole file system. Of course the
>>> whole segment is free after cleaning, but the live blocks were moved
>>> somewhere else and occupy space there. So from the perspective of the
>>> whole file system you only really gained the amount of space occupied by
>>> the invalidated blocks.
>>>
>>
>> I suggest not to use "free blocks" term for the case of invalidated blocks.
>> Because it is really confusing way. I suppose that we can use term
>> "invalid blocks" or "dead blocks". But I think that "dead blocks" is not
>> good way too. Because, from my point of view, invalidated blocks are
>> blocks that keep previous state of actual blocks. Dead block sounds for
>> me likewise unusable or bad block.
> 
> "free blocks" term sounds confusing.  We often use terms
> "live" and "dead" for garbage collection, but "dead blocks" also
> sounds unfit to me as Vyacheslav pointed out.
> 
> How about "min reclaimable blocks" or "min collectable blocks" ?

Ok I will also change the config options accordingly. I like the term
"reclaimable blocks".

Regards,
Andreas Rohner
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