From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755155AbYKDQGj (ORCPT ); Tue, 4 Nov 2008 11:06:39 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753484AbYKDQGb (ORCPT ); Tue, 4 Nov 2008 11:06:31 -0500 Received: from casper.infradead.org ([85.118.1.10]:45273 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752238AbYKDQGb (ORCPT ); Tue, 4 Nov 2008 11:06:31 -0500 Subject: Re: mmap: is default non-populating behavior stable? From: Peter Zijlstra To: Chris Friesen Cc: Rik van Riel , "Eugene V. Lyubimkin" , linux-kernel@vger.kernel.org, linux-mm , hugh In-Reply-To: <491070B5.2060209@nortel.com> References: <490F73CD.4010705@gmail.com> <1225752083.7803.1644.camel@twins> <490F8005.9020708@redhat.com> <491070B5.2060209@nortel.com> Content-Type: text/plain Content-Transfer-Encoding: 7bit Date: Tue, 04 Nov 2008 17:07:00 +0100 Message-Id: <1225814820.7803.1672.camel@twins> Mime-Version: 1.0 X-Mailer: Evolution 2.24.1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 2008-11-04 at 09:56 -0600, Chris Friesen wrote: > Rik van Riel wrote: > > Peter Zijlstra wrote: > > >> The exact interaction of mmap() and truncate() I'm not exactly clear on. > > > > Truncate will reduce the size of the mmaps on the file to > > match the new file size, so processes accessing beyond the > > end of file will get a segmentation fault (SIGSEGV). > > I suspect Peter was talking about using truncate() to set the initial > file size, effectively increasing rather than reducing it. I was thinking of truncate() on an already mmap()'ed region, either increasing or decreasing the size so that part of the mmap becomes (in)valid. I'm not sure how POSIX speaks of this. I think Linux does the expected thing.