From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Wed, 2 May 2001 10:47:00 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Wed, 2 May 2001 10:46:50 -0400 Received: from nat-pool.corp.redhat.com ([199.183.24.200]:43959 "EHLO devserv.devel.redhat.com") by vger.kernel.org with ESMTP id ; Wed, 2 May 2001 10:46:42 -0400 Date: Wed, 2 May 2001 14:43:23 +0100 From: "Stephen C. Tweedie" To: Hugh Dickins Cc: "Stephen C. Tweedie" , Rogier Wolff , Alan Cox , "J . A . Magallon" , Wakko Warner , Xavier Bestel , Goswin Brederlow , William T Wilson , Matt_Domsch@Dell.com, linux-kernel@vger.kernel.org Subject: Re: 2.4 and 2GB swap partition limit Message-ID: <20010502144323.I26638@redhat.com> In-Reply-To: <20010502120403.G26638@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.2i In-Reply-To: ; from hugh@veritas.com on Wed, May 02, 2001 at 01:49:16PM +0100 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Hi, On Wed, May 02, 2001 at 01:49:16PM +0100, Hugh Dickins wrote: > On Wed, 2 May 2001, Stephen C. Tweedie wrote: > > > > So the aim is more complex. Basically, once we are short on VM, we > > want to eliminate redundant copies of swap data. That implies two > > possible actions, not one --- we can either remove the swap page for > > data which is already in memory, or we can remove the in-memory copy > > of data which is already on swap. Which one is appropriate will > > depend on whether the ptes in the system point to the swap entry or > > the memory entry. If we have ptes pointing to both, then we cannot > > free either. > > Sorry for stating the obvious, but that last sentence gives up too easily. > If we have ptes pointing to both, then we cannot free either until we have > replaced all the references to one by references to the other. Sure, but it's far from obvious that we need to worry about this. 2.2 has exactly this same behaviour for shared pages, and so if people are complaining about a 2.4 regression, this particular aspect of the behaviour is clearly not the underlying problem. --Stephen