Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754593AbYBKKQx (ORCPT ); Mon, 11 Feb 2008 05:16:53 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752021AbYBKKQo (ORCPT ); Mon, 11 Feb 2008 05:16:44 -0500 Received: from x346.tv-sign.ru ([89.108.83.215]:35595 "EHLO mail.screens.ru" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752003AbYBKKQn (ORCPT ); Mon, 11 Feb 2008 05:16:43 -0500 Date: Mon, 11 Feb 2008 13:15:30 +0300 From: Oleg Nesterov To: Hugh Dickins Cc: Miklos Szeredi , Andrew Morton , Peter Zijlstra , William Lee Irwin III , Nick Piggin , Ingo Molnar , linux-kernel@vger.kernel.org, Matt Helsley Subject: Re: [PATCH] sys_remap_file_pages: fix ->vm_file accounting Message-ID: <20080211101530.GA162@tv-sign.ru> References: <20080130142014.GA2164@tv-sign.ru> <1201712101.31222.22.camel@tucsk.pomaz.szeredi.hu> <20080130172646.GA2355@tv-sign.ru> <20080203182952.GB5827@tv-sign.ru> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.11 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1422 Lines: 39 Sorry for delay, On 02/06, Hugh Dickins wrote: > > On Sun, 3 Feb 2008, Oleg Nesterov wrote: > > Off-topic question to all. sys_remap_file_pages() doesn't work with > > shared readonly mappings, why? > > Slight correction: it works with shared readonly mappings, doesn't > it, so long as the mmap'ed file was opened for reading and writing? Yes sure. I meant, if the file was opened without FMODE_WRITE, then mmap(PROT_READ, MAP_SHARED) doesn't actually set VM_SHARED, it only sets VM_MAYSHARE. (this looks understandable, but means that !VM_SHARED doesn't necessary imply the possible cow). > > IOW, why it checks VM_SHARED but not VM_MAYSHARE? > > My guess has always been that it was just a misunderstanding of how > those VM_ flags end up working: assume so unless Ingo corrects me. > > By the time I realized that oddity, we'd been driven into several > tiresome corners by the very existence of sys_remap_file_pages. > So whereas my usual instinct would have been to relax the restriction > and generalize, in its case I wanted to hold on to every restriction > we had. OK, thanks a lot. I was afraid I missed some "obvious" reason why we can't do this. Oleg. -- 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/