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Date: Thu, 11 Apr 2013 11:01:11 -0400
From: KOSAKI Motohiro <kosaki.motohiro@gmail.com>
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Subject: Re: [RFC v7 00/11] Support vrange for anonymous page
References: <1363073915-25000-1-git-send-email-minchan@kernel.org> <5165CA22.6080808@gmail.com> <20130411065546.GA10303@blaptop> <5166643E.6050704@gmail.com> <20130411080243.GA12626@blaptop> <5166712C.7040802@gmail.com> <20130411083146.GB12626@blaptop>
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Cc: KOSAKI Motohiro <kosaki.motohiro@gmail.com>, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Michael Kerrisk <mtk.manpages@gmail.com>, Arun Sharma <asharma@fb.com>, John Stultz <john.stultz@linaro.org>, Mel Gorman <mel@csn.ul.ie>, Hugh Dickins <hughd@google.com>, Dave Hansen <dave@linux.vnet.ibm.com>, Rik van Riel <riel@redhat.com>, Neil Brown <neilb@suse.de>, Mike Hommey <mh@glandium.org>, Taras Glek <tglek@mozilla.com>, KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>, KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>, Jason Evans <je@fb.com>, sanjay@google.com, Paul Turner <pjt@google.com>, Johannes Weiner <hannes@cmpxchg.org>, Michel Lespinasse <walken@google.com>, Andrew Morton <akpm@linux-foundation.org>

>>>> 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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