From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1765243AbZFQOM6 (ORCPT ); Wed, 17 Jun 2009 10:12:58 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755097AbZFQOMv (ORCPT ); Wed, 17 Jun 2009 10:12:51 -0400 Received: from mga03.intel.com ([143.182.124.21]:29915 "EHLO mga03.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754110AbZFQOMt (ORCPT ); Wed, 17 Jun 2009 10:12:49 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.42,236,1243839600"; d="scan'208";a="155594974" Date: Wed, 17 Jun 2009 22:12:37 +0800 From: Wu Fengguang To: Minchan Kim Cc: Andrew Morton , LKML , Andi Kleen , Ingo Molnar , Mel Gorman , Thomas Gleixner , "H. Peter Anvin" , Peter Zijlstra , Nick Piggin , Hugh Dickins , Andi Kleen , "riel@redhat.com" , "chris.mason@oracle.com" , "linux-mm@kvack.org" Subject: Re: [PATCH 09/22] HWPOISON: Handle hardware poisoned pages in try_to_unmap Message-ID: <20090617141237.GA8528@localhost> References: <20090615152612.GA11700@localhost> <20090616090308.bac3b1f7.minchan.kim@barrios-desktop> <20090616134944.GB7524@localhost> <20090617092826.56730a10.minchan.kim@barrios-desktop> <20090617072319.GA5841@localhost> <28c262360906170627p2e57f907y2f8bbdc9fd5804f2@mail.gmail.com> <20090617133708.GA7839@localhost> <28c262360906170643o3783b0a4k8fbc1001baa8e2e1@mail.gmail.com> <20090617140334.GB8079@localhost> <28c262360906170708u467f9324qf218c0c6f5fa434f@mail.gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <28c262360906170708u467f9324qf218c0c6f5fa434f@mail.gmail.com> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jun 17, 2009 at 10:08:13PM +0800, Minchan Kim wrote: > On Wed, Jun 17, 2009 at 11:03 PM, Wu Fengguang wrote: > > On Wed, Jun 17, 2009 at 09:43:29PM +0800, Minchan Kim wrote: > >> On Wed, Jun 17, 2009 at 10:37 PM, Wu Fengguang wrote: > >> > On Wed, Jun 17, 2009 at 09:27:36PM +0800, Minchan Kim wrote: > >> >> On Wed, Jun 17, 2009 at 4:23 PM, Wu Fengguang wrote: > >> >> > On Wed, Jun 17, 2009 at 08:28:26AM +0800, Minchan Kim wrote: > >> >> >> On Tue, 16 Jun 2009 21:49:44 +0800 > >> >> >> Wu Fengguang wrote: > >> >> >> > >> >> >> > On Tue, Jun 16, 2009 at 08:03:08AM +0800, Minchan Kim wrote: > >> >> >> > > On Mon, 15 Jun 2009 23:26:12 +0800 > >> >> >> > > Wu Fengguang wrote: > >> >> >> > > > >> >> >> > > > On Mon, Jun 15, 2009 at 09:09:03PM +0800, Minchan Kim wrote: > >> >> >> > > > > On Mon, Jun 15, 2009 at 11:45 AM, Wu Fengguang wrote: > >> >> >> > > > > > From: Andi Kleen > >> >> >> > > > > > > >> >> >> > > > > > When a page has the poison bit set replace the PTE with a poison entry. > >> >> >> > > > > > This causes the right error handling to be done later when a process runs > >> >> >> > > > > > into it. > >> >> >> > > > > > > >> >> >> > > > > > Also add a new flag to not do that (needed for the memory-failure handler > >> >> >> > > > > > later) > >> >> >> > > > > > > >> >> >> > > > > > Reviewed-by: Wu Fengguang > >> >> >> > > > > > Signed-off-by: Andi Kleen > >> >> >> > > > > > > >> >> >> > > > > > --- > >> >> >> > > > > >  include/linux/rmap.h |    1 + > >> >> >> > > > > >  mm/rmap.c            |    9 ++++++++- > >> >> >> > > > > >  2 files changed, 9 insertions(+), 1 deletion(-) > >> >> >> > > > > > > >> >> >> > > > > > --- sound-2.6.orig/mm/rmap.c > >> >> >> > > > > > +++ sound-2.6/mm/rmap.c > >> >> >> > > > > > @@ -958,7 +958,14 @@ static int try_to_unmap_one(struct page > >> >> >> > > > > >        /* Update high watermark before we lower rss */ > >> >> >> > > > > >        update_hiwater_rss(mm); > >> >> >> > > > > > > >> >> >> > > > > > -       if (PageAnon(page)) { > >> >> >> > > > > > +       if (PageHWPoison(page) && !(flags & TTU_IGNORE_HWPOISON)) { > >> >> >> > > > > > +               if (PageAnon(page)) > >> >> >> > > > > > +                       dec_mm_counter(mm, anon_rss); > >> >> >> > > > > > +               else if (!is_migration_entry(pte_to_swp_entry(*pte))) > >> >> >> > > > > > >> >> >> > > > > Isn't it straightforward to use !is_hwpoison_entry ? > >> >> >> > > > > >> >> >> > > > Good catch!  It looks like a redundant check: the > >> >> >> > > > page_check_address() at the beginning of the function guarantees that > >> >> >> > > > !is_migration_entry() or !is_migration_entry() tests will all be TRUE. > >> >> >> > > > So let's do this? > >> >> >> > > It seems you expand my sight :) > >> >> >> > > > >> >> >> > > I don't know migration well. > >> >> >> > > How page_check_address guarantee it's not migration entry ? > >> >> >> > > >> >> >> > page_check_address() calls pte_present() which returns the > >> >> >> > (_PAGE_PRESENT | _PAGE_PROTNONE) bits. While x86-64 defines > >> >> >> > > >> >> >> > #define __swp_entry(type, offset)       ((swp_entry_t) { \ > >> >> >> >                                          ((type) << (_PAGE_BIT_PRESENT + 1)) \ > >> >> >> >                                          | ((offset) << SWP_OFFSET_SHIFT) }) > >> >> >> > > >> >> >> > where SWP_OFFSET_SHIFT is defined to the bigger one of > >> >> >> > max(_PAGE_BIT_PROTNONE + 1, _PAGE_BIT_FILE + 1) = max(8+1, 6+1) = 9. > >> >> >> > > >> >> >> > So __swp_entry(type, offset) := (type << 1) | (offset << 9) > >> >> >> > > >> >> >> > We know that the swap type is 5 bits. So the bit 0 _PAGE_PRESENT and bit 8 > >> >> >> > _PAGE_PROTNONE will all be zero for swap entries. > >> >> >> > > >> >> >> > >> >> >> Thanks for kind explanation :) > >> >> > > >> >> > You are welcome~ > >> >> > > >> >> >> > > >> >> >> > > In addtion, If the page is poison while we are going to > >> >> >> > > migration((PAGE_MIGRATION && migration) == TRUE), we should decrease > >> >> >> > > file_rss ? > >> >> >> > > >> >> >> > It will die on trying to migrate the poisoned page so we don't care > >> >> >> > the accounting. But normally the poisoned page shall already be > >> >> >> > >> >> >> > >> >> >> Okay. then, how about this ? > >> >> >> We should not increase file_rss on trying to migrate the poisoned page > >> >> >> > >> >> >> -               else if (!is_migration_entry(pte_to_swp_entry(*pte))) > >> >> >> +               else if (!(PAGE_MIGRATION && migration)) > >> >> > > >> >> > This is good if we are going to stop the hwpoison page from being > >> >> > consumed by move_to_new_page(), but I highly doubt we'll ever add > >> >> > PageHWPoison() checks into the migration code. > >> >> > > >> >> > Because this race window is small enough: > >> >> > > >> >> >        TestSetPageHWPoison(p); > >> >> >                                   lock_page(page); > >> >> >                                   try_to_unmap(page, TTU_MIGRATION|...); > >> >> >        lock_page_nosync(p); > >> >> > > >> >> > such small race windows can be found all over the kernel, it's just > >> >> > insane to try to fix any of them. > >> >> > >> >> Sorry for too late response. > >> >> > >> >> I see your point. > >> >> My opinion is that at least we must be notified when such situation happen. > >> >> So I think it would be better to add some warning to fix up it when it > >> >> happen even thought  it is small race window. > >> > > >> > Notification is also pointless here: we'll die hard on > >> > accessing/consuming the poisoned page anyway :( > >> > >> My intention wasn't to recover it. > > > > Yes, that's not the point. > > > >> It just add something like WARN_ON. > >> You said it is small window enough. but I think it can happen more > >> hight probability in migration-workload.(At a moment, I don't know > >> what kinds of app) > >> For such case, If we can hear reporting of warning, at that time we > >> can consider migration handling for HWPoison. > > > > The point is, any page can go corrupted any time. We don't need to add > > 1000 PageHWPoison() tests in the kernel like this. We don't aim for > > 100% protection, that's impossible. I'd be very contented if ever it > > can reach 80% coverage :) > > Okay. > If it is your goal, I also think migration portion of all is very small. > Thanks for kind reply for my boring discussion. > > Reviewed-by : Minchan Kim Thank you, I'll add comments to clearly state that goal and its rational :)