From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754841AbZFQN1n (ORCPT ); Wed, 17 Jun 2009 09:27:43 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752096AbZFQN1f (ORCPT ); Wed, 17 Jun 2009 09:27:35 -0400 Received: from yw-out-2324.google.com ([74.125.46.29]:33612 "EHLO yw-out-2324.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751796AbZFQN1e convert rfc822-to-8bit (ORCPT ); Wed, 17 Jun 2009 09:27:34 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :cc:content-type:content-transfer-encoding; b=CwNLC9Mnk5gCmzt1uX7xOyYOKSOCfkcsaAjyI6TfyQHEP5r5q51autoRzeBWuRuuSB 8N4Vi2SucCfw+odkNzSDeULhz0c9yqUk4hDwDEKDhkB6QfJb9FSC5a5RG0mFoNITJJwW CYx4pH0acC0c/tat9z2qlQZJGAAmQqSPw751A= MIME-Version: 1.0 In-Reply-To: <20090617072319.GA5841@localhost> References: <20090615024520.786814520@intel.com> <20090615031253.530308256@intel.com> <28c262360906150609gd736bf7p7a57de1b81cedd97@mail.gmail.com> <20090615152612.GA11700@localhost> <20090616090308.bac3b1f7.minchan.kim@barrios-desktop> <20090616134944.GB7524@localhost> <20090617092826.56730a10.minchan.kim@barrios-desktop> <20090617072319.GA5841@localhost> Date: Wed, 17 Jun 2009 22:27:36 +0900 Message-ID: <28c262360906170627p2e57f907y2f8bbdc9fd5804f2@mail.gmail.com> Subject: Re: [PATCH 09/22] HWPOISON: Handle hardware poisoned pages in try_to_unmap From: Minchan Kim To: Wu Fengguang 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" Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. -- Kinds regards, Minchan Kim