From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail172.messagelabs.com (mail172.messagelabs.com [216.82.254.3]) by kanga.kvack.org (Postfix) with SMTP id DDCE66B0055 for ; Wed, 17 Jun 2009 09:37:24 -0400 (EDT) Date: Wed, 17 Jun 2009 21:37:08 +0800 From: Wu Fengguang Subject: Re: [PATCH 09/22] HWPOISON: Handle hardware poisoned pages in try_to_unmap Message-ID: <20090617133708.GA7839@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> <28c262360906170627p2e57f907y2f8bbdc9fd5804f2@mail.gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <28c262360906170627p2e57f907y2f8bbdc9fd5804f2@mail.gmail.com> Sender: owner-linux-mm@kvack.org 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" List-ID: 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 > >> > > > > > > >> > > > > > --- > >> > > > > > A include/linux/rmap.h | A A 1 + > >> > > > > > A mm/rmap.c A A A A A A | A A 9 ++++++++- > >> > > > > > A 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 > >> > > > > > A A A A /* Update high watermark before we lower rss */ > >> > > > > > A A A A update_hiwater_rss(mm); > >> > > > > > > >> > > > > > - A A A if (PageAnon(page)) { > >> > > > > > + A A A if (PageHWPoison(page) && !(flags & TTU_IGNORE_HWPOISON)) { > >> > > > > > + A A A A A A A if (PageAnon(page)) > >> > > > > > + A A A A A A A A A A A dec_mm_counter(mm, anon_rss); > >> > > > > > + A A A A A A A else if (!is_migration_entry(pte_to_swp_entry(*pte))) > >> > > > > > >> > > > > Isn't it straightforward to use !is_hwpoison_entry ? > >> > > > > >> > > > Good catch! A 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) A A A ((swp_entry_t) { \ > >> > A A A A A A A A A A A A A A A A A A A A A ((type) << (_PAGE_BIT_PRESENT + 1)) \ > >> > A A A A A A A A A A A A A A A A A A A A A | ((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 > >> > >> - A A A A A A A else if (!is_migration_entry(pte_to_swp_entry(*pte))) > >> + A A A A A A A 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: > > > > A A A A TestSetPageHWPoison(p); > > A A A A A A A A A A A A A A A A A lock_page(page); > > A A A A A A A A A A A A A A A A A try_to_unmap(page, TTU_MIGRATION|...); > > A A A A 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 :( Thanks, Fengguang -- 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