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

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Date:	Thu, 11 Apr 2013 11:01:11 -0400
From:	KOSAKI Motohiro <kosaki.motohiro@...il.com>
To:	Minchan Kim <minchan@...nel.org>
CC:	KOSAKI Motohiro <kosaki.motohiro@...il.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	Michael Kerrisk <mtk.manpages@...il.com>,
	Arun Sharma <asharma@...com>,
	John Stultz <john.stultz@...aro.org>,
	Mel Gorman <mel@....ul.ie>, Hugh Dickins <hughd@...gle.com>,
	Dave Hansen <dave@...ux.vnet.ibm.com>,
	Rik van Riel <riel@...hat.com>, Neil Brown <neilb@...e.de>,
	Mike Hommey <mh@...ndium.org>, Taras Glek <tglek@...illa.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Jason Evans <je@...com>, sanjay@...gle.com,
	Paul Turner <pjt@...gle.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Michel Lespinasse <walken@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [RFC v7 00/11] Support vrange for anonymous page

>>>> 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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