Re: [RFC v7 00/11] Support vrange for anonymous page

[KOSAKI Motohiro]

>>>> and adding new syscall invokation is unwelcome.
>>>
>>> Sure. But one more system call could be cheaper than page-granuarity
>>> operation on purged range.
>>
>> I don't think vrange(VOLATILE) cost is the related of this discusstion.
>> Whether sending SIGBUS or just nuke pte, purge should be done on vmscan,
>> not vrange() syscall.
> 
> Again, please see the MADV_FREE. http://lwn.net/Articles/230799/
> It does changes pte and page flags on all pages of the range through
> zap_pte_range. So it would make vrange(VOLASTILE) expensive and
> the bigger cost is, the bigger range is.

This haven't been crossed my mind. now try_to_discard_one() insert vrange
for making SIGBUS. then, we can insert pte_none() as the same cost too. Am
I missing something?

I couldn't imazine why pte should be zapping on vrange(VOLATILE).
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