Messages in this thread | | | Date | Wed, 17 Jun 2009 22:12:37 +0800 | From | Wu Fengguang <> | Subject | Re: [PATCH 09/22] HWPOISON: Handle hardware poisoned pages in try_to_unmap |
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On Wed, Jun 17, 2009 at 10:08:13PM +0800, Minchan Kim wrote: > On Wed, Jun 17, 2009 at 11:03 PM, Wu Fengguang<fengguang.wu@intel.com> 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<fengguang.wu@intel.com> 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<fengguang.wu@intel.com> 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 <fengguang.wu@intel.com> 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 <fengguang.wu@intel.com> 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<fengguang.wu@intel.com> wrote: > >> >> >> > > > > > From: Andi Kleen <ak@linux.intel.com> > >> >> >> > > > > > > >> >> >> > > > > > 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 <fengguang.wu@intel.com> > >> >> >> > > > > > Signed-off-by: Andi Kleen <ak@linux.intel.com> > >> >> >> > > > > > > >> >> >> > > > > > --- > >> >> >> > > > > > 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 <minchan.kim@gmail.com>
Thank you, I'll add comments to clearly state that goal and its rational :)
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