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

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Message-ID: <20081105165405.777ab502@lxorguk.ukuu.org.uk>
Date:	Wed, 5 Nov 2008 16:54:05 +0000
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Hugh Dickins <hugh@...itas.com>
Cc:	"Eugene V. Lyubimkin" <jackyf.devel@...il.com>,
	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>
Subject: Re: mmap: is default non-populating behavior stable?

> (Every year or so we do wonder whether to change an extending mremap
> of a MAP_SHARED|MAP_ANONYMOUS object to extend the object itself instead
> of just SIGBUSing on the extension: but I've so far remained conservative
> about that, and Eugene appears to be thinking of more ordinary files.)

Try an mremap of a VM_GROWS* mapping and all the other things of this
nature. I would say our current behaviour is not what might be expected
by users. The extending an object case is just one example of weird
behaviour.

Alan


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