Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759931AbZDOLnv (ORCPT ); Wed, 15 Apr 2009 07:43:51 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1759757AbZDOLnj (ORCPT ); Wed, 15 Apr 2009 07:43:39 -0400 Received: from mx2.redhat.com ([66.187.237.31]:33504 "EHLO mx2.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1759702AbZDOLnh (ORCPT ); Wed, 15 Apr 2009 07:43:37 -0400 Date: Wed, 15 Apr 2009 13:41:54 +0200 From: Andrea Arcangeli To: KOSAKI Motohiro Cc: Nick Piggin , LKML , Linus Torvalds , Andrew Morton , Jeff Moyer , linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, Hugh Dickins Subject: Re: [RFC][PATCH v3 1/6] mm: Don't unmap gup()ed page Message-ID: <20090415114154.GI9809@random.random> References: <20090414143252.GE28265@random.random> <200904150042.15653.nickpiggin@yahoo.com.au> <20090415165431.AC4C.A69D9226@jp.fujitsu.com> <20090415104615.GG9809@random.random> <2f11576a0904150439k6e828307ja97b6729650bcb94@mail.gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <2f11576a0904150439k6e828307ja97b6729650bcb94@mail.gmail.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1763 Lines: 38 On Wed, Apr 15, 2009 at 08:39:04PM +0900, KOSAKI Motohiro wrote: > >> + ? ? if (!migration) { > >> + ? ? ? ? ? ? /* re-check */ > >> + ? ? ? ? ? ? if (PageSwapCache(page) && > >> + ? ? ? ? ? ? ? ? page_count(page) != page_mapcount(page) + 2) { > >> + ? ? ? ? ? ? ? ? ? ? /* We lose race against get_user_pages_fast() */ > >> + ? ? ? ? ? ? ? ? ? ? set_pte_at(mm, address, pte, pteval); > >> + ? ? ? ? ? ? ? ? ? ? ret = SWAP_FAIL; > >> + ? ? ? ? ? ? ? ? ? ? goto out_unmap; > >> + ? ? ? ? ? ? } > >> + ? ? } > >> + ? ? mmu_notifier_invalidate_page(vma->vm_mm, address); > > > > With regard to mmu notifier, this is the opposite of the right > > ordering. One mmu_notifier_invalidate_page must run _before_ the first > > check. The ptep_clear_flush_notify will then stay and there's no need > > of a further mmu_notifier_invalidate_page after the second check. > > OK. but I have one question. > > Can we assume mmu_notifier is only used by kvm now? > if not, we need to make new notifier. KVM is no fundamentally different from other users in this respect, so I don't see why need a new notifier. If it works for others it'll work for KVM and the other way around is true too. mmu notifier users can or cannot take a page pin. KVM does. GRU doesn't. XPMEM does. All of them releases any pin after mmu_notifier_invalidate_page. All that is important is to run mmu_notifier_invalidate_page _after_ the ptep_clear_young_notify, so that we don't nuke secondary mappings on the pages unless we really go to nuke the pte. -- 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/