From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail172.messagelabs.com (mail172.messagelabs.com [216.82.254.3]) by kanga.kvack.org (Postfix) with ESMTP id 89D3C8D0046 for ; Thu, 17 Mar 2011 15:56:27 -0400 (EDT) Date: Thu, 17 Mar 2011 12:54:27 -0700 From: Andrew Morton Subject: Re: [Resend] Cross Memory Attach v3 [PATCH] Message-Id: <20110317125427.eebbfb51.akpm@linux-foundation.org> In-Reply-To: <20110317154026.61ddd925@lilo> References: <20110315143547.1b233cd4@lilo> <20110315161623.4099664b.akpm@linux-foundation.org> <20110317154026.61ddd925@lilo> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Christopher Yeoh Cc: linux-mm@kvack.org, Linus Torvalds 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. -- 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