From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail143.messagelabs.com (mail143.messagelabs.com [216.82.254.35]) by kanga.kvack.org (Postfix) with SMTP id 6E2566B006A for ; Wed, 17 Jun 2009 09:26:48 -0400 (EDT) Received: by gxk28 with SMTP id 28so558555gxk.14 for ; Wed, 17 Jun 2009 06:27:36 -0700 (PDT) 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 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Sender: owner-linux-mm@kvack.org 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" List-ID: 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 pois= on entry. >> > > > > > This causes the right error handling to be done later when a p= rocess runs >> > > > > > into it. >> > > > > > >> > > > > > Also add a new flag to not do that (needed for the memory-fail= ure handler >> > > > > > later) >> > > > > > >> > > > > > Reviewed-by: Wu Fengguang >> > > > > > Signed-off-by: Andi Kleen >> > > > > > >> > > > > > --- >> > > > > > =C2=A0include/linux/rmap.h | =C2=A0 =C2=A01 + >> > > > > > =C2=A0mm/rmap.c =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0| =C2= =A0 =C2=A09 ++++++++- >> > > > > > =C2=A02 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 >> > > > > > =C2=A0 =C2=A0 =C2=A0 =C2=A0/* Update high watermark before we = lower rss */ >> > > > > > =C2=A0 =C2=A0 =C2=A0 =C2=A0update_hiwater_rss(mm); >> > > > > > >> > > > > > - =C2=A0 =C2=A0 =C2=A0 if (PageAnon(page)) { >> > > > > > + =C2=A0 =C2=A0 =C2=A0 if (PageHWPoison(page) && !(flags & TTU= _IGNORE_HWPOISON)) { >> > > > > > + =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 if (PageAno= n(page)) >> > > > > > + =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2= =A0 =C2=A0 =C2=A0 dec_mm_counter(mm, anon_rss); >> > > > > > + =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 else if (!i= s_migration_entry(pte_to_swp_entry(*pte))) >> > > > > >> > > > > Isn't it straightforward to use !is_hwpoison_entry ? >> > > > >> > > > Good catch! =C2=A0It looks like a redundant check: the >> > > > page_check_address() at the beginning of the function guarantees t= hat >> > > > !is_migration_entry() or !is_migration_entry() tests will all be T= RUE. >> > > > 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) =C2=A0 =C2=A0 =C2=A0 ((swp_entry_t) = { \ >> > =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 = =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2= =A0((type) << (_PAGE_BIT_PRESENT + 1)) \ >> > =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 = =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2= =A0| ((offset) << SWP_OFFSET_SHIFT) }) >> > >> > where SWP_OFFSET_SHIFT is defined to the bigger one of >> > max(_PAGE_BIT_PROTNONE + 1, _PAGE_BIT_FILE + 1) =3D max(8+1, 6+1) =3D = 9. >> > >> > So __swp_entry(type, offset) :=3D (type << 1) | (offset << 9) >> > >> > We know that the swap type is 5 bits. So the bit 0 _PAGE_PRESENT and b= it 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) =3D=3D TRUE), we should decr= ease >> > > 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 >> >> - =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 else if (!is_migratio= n_entry(pte_to_swp_entry(*pte))) >> + =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 else if (!(PAGE_MIGRA= TION && 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: > > =C2=A0 =C2=A0 =C2=A0 =C2=A0TestSetPageHWPoison(p); > =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2= =A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 lock_page(page); > =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2= =A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 try_to_unmap(page, TTU_MIGRAT= ION|...); > =C2=A0 =C2=A0 =C2=A0 =C2=A0lock_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. --=20 Kinds regards, Minchan Kim -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org