From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760178AbYEMSJ2 (ORCPT ); Tue, 13 May 2008 14:09:28 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754453AbYEMSJV (ORCPT ); Tue, 13 May 2008 14:09:21 -0400 Received: from mx1.redhat.com ([66.187.233.31]:60756 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753756AbYEMSJU (ORCPT ); Tue, 13 May 2008 14:09:20 -0400 Date: Tue, 13 May 2008 14:09:02 -0400 From: Rik van Riel To: Lee Schermerhorn Cc: Daisuke Nishimura , akpm@linux-foundation.org, kosaki.motohiro@jp.fujitsu.com, linux-kernel@vger.kernel.org Subject: Re: [PATCH] take pageout refcount into account for remove_exclusive_swap_page Message-ID: <20080513140902.1030afaa@cuia.bos.redhat.com> In-Reply-To: <1210700635.6208.40.camel@lts-notebook> References: <20080428181835.502876582@redhat.com> <20080428181852.620969450@redhat.com> <4828283C.4000803@mxp.nes.nec.co.jp> <20080512093307.2ace3096@bree.surriel.com> <482990FC.3020303@mxp.nes.nec.co.jp> <20080513120417.0833cec1@cuia.bos.redhat.com> <1210700635.6208.40.camel@lts-notebook> Organization: Red Hat, Inc X-Mailer: Claws Mail 3.3.1 (GTK+ 2.12.5; i386-redhat-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 13 May 2008 13:43:55 -0400 Lee Schermerhorn wrote: > Or, more generally, 2 + N, for an anon page that is mapped [must be > read-only, right?] by N processes. This can happen after, e.g., fork(). > Looks like this patch handles the condition just fine, but you might > want to reflect this in the comment. No, this patch only removes a page from the swap cache that is mapped by one process. The function page_mapped() returns either 1 or 0, not the same as page_mapcount(). I am not sure if trying to handle swap cache pages that are mapped by multiple processes could get us into other corner cases and think that we should probably try to stick to the safe thing for now. Besides, shouldn't anonymous shared pages be COW and relatively rare? > Now, I think I can use this to try to remove anon pages from the swap > cache when they're mlocked. > > > + */ > > +int remove_exclusive_swap_page_ref(struct page *page) > > +{ > > + return remove_exclusive_swap_page_count(page, 2 + page_mapped(page)); > > +} > > + > > +/* > > * Free the swap entry like above, but also try to > > * free the page cache entry if it is the last user. > > */ > > > > All Rights Reversed -- All Rights Reversed