Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Mon, 14 Oct 2002 09:50:27 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Mon, 14 Oct 2002 09:50:27 -0400 Received: from holomorphy.com ([66.224.33.161]:3471 "EHLO holomorphy") by vger.kernel.org with ESMTP id ; Mon, 14 Oct 2002 09:50:26 -0400 Date: Mon, 14 Oct 2002 06:52:32 -0700 From: William Lee Irwin III To: Ingo Molnar Cc: Linus Torvalds , linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [patch, feature] nonlinear mappings, prefaulting support, 2.5.42-F8 Message-ID: <20021014135232.GB4488@holomorphy.com> Mail-Followup-To: William Lee Irwin III , Ingo Molnar , Linus Torvalds , linux-kernel@vger.kernel.org, linux-mm@kvack.org References: Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.3.25i Organization: The Domain of Holomorphy Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1879 Lines: 41 On Mon, Oct 14, 2002 at 02:38:43PM +0200, Ingo Molnar wrote: > the patch has got an initial review from Linus, Andrew Morton and Hugh > Dickins, and most of their suggestions are part of the patch already. hmm On Mon, Oct 14, 2002 at 02:38:43PM +0200, Ingo Molnar wrote: > +int sys_remap_file_pages(unsigned long start, unsigned long size, > + unsigned long prot, unsigned long pgoff, unsigned long flags) ISTR suggesting vectorizing this to reduce syscall traffic. The semantics of faulting in pages on such a region, while not incorrect, are at least unusual enough to raise the question of whether it's appropriate for the kernel to fill the pages as opposed to returning an error to userspace. The requirement of MAP_LOCKED or PROT_NONE might as well be in-kernel if the file offset contiguity assumption is not met, since there's no reliable way for userspace to use the syscall otherwise. sys_remap_file_pages() also interacts in an unusual way with the semantics of MAP_POPULATE. MAP_POPULATE seems to perform a non-blocking make_pages_present() operation not shared with MAP_LOCKED, and filemap_populate() performs the file offset contiguous prefaulting which again doesn't mix well with the scatter gather semantics desired. These are the file offset contiguity assumptions I mentioned. Also, a stranger phenomenon appears in filemap_populate(), where nonblock may be true, and so filemap_getpage() will return NULL, but -ENOMEM is returned if filemap_getpage() returns NULL. Also, I see a significant portion of filemap_nopage() duplicated in filemap_getpage(), including long-stale hashtable-related comments. Bill - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/