From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S264729AbUEYE7m (ORCPT ); Tue, 25 May 2004 00:59:42 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S264727AbUEYE7m (ORCPT ); Tue, 25 May 2004 00:59:42 -0400 Received: from fw.osdl.org ([65.172.181.6]:17886 "EHLO mail.osdl.org") by vger.kernel.org with ESMTP id S264725AbUEYE7l (ORCPT ); Tue, 25 May 2004 00:59:41 -0400 Date: Mon, 24 May 2004 21:59:36 -0700 (PDT) From: Linus Torvalds To: Andrea Arcangeli cc: Benjamin Herrenschmidt , Andrew Morton , Linux Kernel list , Ingo Molnar , Ben LaHaise , linux-mm@kvack.org, Architectures Group Subject: Re: [PATCH] ppc64: Fix possible race with set_pte on a present PTE In-Reply-To: <20040525045059.GW29378@dualathlon.random> Message-ID: References: <1085369393.15315.28.camel@gaston> <1085371988.15281.38.camel@gaston> <1085373839.14969.42.camel@gaston> <20040525034326.GT29378@dualathlon.random> <20040525042054.GU29378@dualathlon.random> <20040525045059.GW29378@dualathlon.random> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 25 May 2004, Andrea Arcangeli wrote: > > no, that's not what I remeber from alpha, alpha always sets the young > bit as soon as it sets the pte from non-null to something. Yes. However, whtn the page is _aged_ later, the young bits will be cleared. And _that_ is when you will now start getting infinite page faults, because with your patch the young bits will never be set again on a normal read. See what I'm saying? Your patch literally leaves the page table alone on pure reads. Which is not acceptable, since the page being marked old was what caused the read-fault in the first place. But yes, pages will be young by default, so you won't ever actually _see_ this behaviour until you start having memory pressure and VM reclaim starts trying to age the things. Linus