linux-kernel - Re: mmap: is default non-populating behavior stable?

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Date:	Tue, 04 Nov 2008 18:51:36 +0200
From:	"Eugene V. Lyubimkin" <jackyf.devel@...il.com>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
CC:	Peter Zijlstra <peterz@...radead.org>,
	Chris Friesen <cfriesen@...tel.com>,
	Rik van Riel <riel@...hat.com>, linux-kernel@...r.kernel.org,
	linux-mm <linux-mm@...ck.org>, hugh <hugh@...itas.com>
Subject: Re: mmap: is default non-populating behavior stable?

Alan Cox wrote:
> On Tue, 04 Nov 2008 17:07:00 +0100
> Peter Zijlstra <peterz@...radead.org> wrote:
>> [snip]
>> I'm not sure how POSIX speaks of this.
>>
>> I think Linux does the expected thing.
> 
> I believe our behaviour is correct for mmap/mumap/truncate and it
> certainly used to be and was tested.
> 
> At the point you do anything involving mremap (which is non posix) our
> behaviour becomes rather bizarre.

Thanks to all for answers. I have made the conclusion that doing "open() new
file, truncate(<big size>), mmap(<the same big size>), write/read some memory
pages" should not populate other, untouched by write/read pages (until
MAP_POPULATE given), right?

-- 
Eugene V. Lyubimkin aka JackYF


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