Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752573AbYKLDL2 (ORCPT ); Tue, 11 Nov 2008 22:11:28 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751156AbYKLDLR (ORCPT ); Tue, 11 Nov 2008 22:11:17 -0500 Received: from nlpi025.sbcis.sbc.com ([207.115.36.54]:35351 "EHLO nlpi025.prodigy.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751111AbYKLDLQ (ORCPT ); Tue, 11 Nov 2008 22:11:16 -0500 Date: Tue, 11 Nov 2008 21:10:45 -0600 (CST) From: Christoph Lameter X-X-Sender: cl@quilx.com To: Andrea Arcangeli cc: Andrew Morton , Izik Eidus , linux-kernel@vger.kernel.org, linux-mm@kvack.org, kvm@vger.kernel.org, chrisw@redhat.com, avi@redhat.com, izike@qumranet.com Subject: Re: [PATCH 2/4] Add replace_page(), change the mapping of pte from one page into another In-Reply-To: <20081112022701.GT10818@random.random> Message-ID: References: <1226409701-14831-1-git-send-email-ieidus@redhat.com> <1226409701-14831-2-git-send-email-ieidus@redhat.com> <1226409701-14831-3-git-send-email-ieidus@redhat.com> <20081111114555.eb808843.akpm@linux-foundation.org> <20081111210655.GG10818@random.random> <20081111221753.GK10818@random.random> <20081111231722.GR10818@random.random> <20081112022701.GT10818@random.random> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII X-Spam-Score: -2.6 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1003 Lines: 19 On Wed, 12 Nov 2008, Andrea Arcangeli wrote: > So are you checking if there's an unresolved reference only in the > very place I just quoted in the previous email? If answer is yes: what > should prevent get_user_pages from running in parallel from another > thread? get_user_pages will trigger a minor fault and get the elevated > reference just after you read page_count. To you it looks like there > is no o_direct in progress when you proceed to the core of migration > code, but in effect o_direct just started a moment after you read the > page count. get_user_pages() cannot get to it since the pagetables have already been modified. If get_user_pages runs then the fault handling will occur which will block the thread until migration is complete. -- 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/