From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail143.messagelabs.com (mail143.messagelabs.com [216.82.254.35]) by kanga.kvack.org (Postfix) with ESMTP id 73E5F8D0039 for ; Sun, 20 Mar 2011 21:50:33 -0400 (EDT) Received: from d23relay05.au.ibm.com (d23relay05.au.ibm.com [202.81.31.247]) by e23smtp06.au.ibm.com (8.14.4/8.13.1) with ESMTP id p2L1oFci018796 for ; Mon, 21 Mar 2011 12:50:15 +1100 Received: from d23av02.au.ibm.com (d23av02.au.ibm.com [9.190.235.138]) by d23relay05.au.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id p2L1oHBD1908740 for ; Mon, 21 Mar 2011 12:50:22 +1100 Received: from d23av02.au.ibm.com (loopback [127.0.0.1]) by d23av02.au.ibm.com (8.14.4/8.13.1/NCO v10.0 AVout) with ESMTP id p2L1oHM7026555 for ; Mon, 21 Mar 2011 12:50:17 +1100 Date: Mon, 21 Mar 2011 12:20:18 +1030 From: Christopher Yeoh Subject: Re: [Resend] Cross Memory Attach v3 [PATCH] Message-ID: <20110321122018.6306d067@lilo> In-Reply-To: <20110317125427.eebbfb51.akpm@linux-foundation.org> References: <20110315143547.1b233cd4@lilo> <20110315161623.4099664b.akpm@linux-foundation.org> <20110317154026.61ddd925@lilo> <20110317125427.eebbfb51.akpm@linux-foundation.org> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Andrew Morton Cc: linux-mm@kvack.org, Linus Torvalds On Thu, 17 Mar 2011 12:54:27 -0700 Andrew Morton wrote: > On Thu, 17 Mar 2011 15:40:26 +1030 > Christopher Yeoh wrote: > > > > Thinking out loud: if we had a way in which a process can add and > > > remove a local anonymous page into pagecache then other processes > > > could access that page via mmap. If both processes map the file > > > with a nonlinear vma they they can happily sit there flipping > > > pages into and out of the shared mmap at arbitrary file offsets. > > > The details might get hairy ;) We wouldn't want all the regular > > > mmap semantics of > > > > Yea, its the complexity of trying to do it that way that eventually > > lead me to implementing it via a syscall and get_user_pages > > instead, trying to keep things as simple as possible. > > The pagecache trick potentially gives zero-copy access, whereas the > proposed code is single-copy. Although the expected benefits of that > may not be so great due to TLB manipulation overheads. > > I worry that one day someone will come along and implement the > pagecache trick, then we're stuck with obsolete code which we have to > maintain for ever. Perhaps I don't understand what you're saying correctly but I think that one problem with the zero copy page flipping approach is that there is no guarantee with the data that the MPI apps want to send resides in a page or pages all by itself. Regards, Chris -- cyeoh@au.ibm.com -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org