Re: [PATCH] mm/memory-failure.c: bail out early if huge zero page

["HORIGUCHI NAOYA(堀口 直也)" <naoya.horiguchi@nec.com>]

On Tue, Apr 12, 2022 at 06:00:09PM +0800, Yu Xu wrote:
> On 4/12/22 5:45 PM, Yu Xu wrote:
...
> > > > > @@ -1087,12 +1087,21 @@ static int madvise_inject_error(int behavior,
> > > > >               return ret;
> > > > >           pfn = page_to_pfn(page);
> > > > > +        head = compound_head(page);
> > > > > +        if (unlikely(is_huge_zero_page(head))) {
> > > > > +            pr_warn("Unhandlable attempt to %s pfn %#lx at
> > > > > process virtual address %#lx\n",
> > > > > +                behavior == MADV_SOFT_OFFLINE ? "soft offline" :
> > > > > +                                "inject memory failure for",
> > > > > +                pfn, start);
> > > > > +            return -EINVAL;
> > > > > +        }
> > > 
> > > This check is about the detail of error handling, so I feel it
> > > desirable to
> > > do this in memory_failure().  And memory errors on huge zero page is the
> > > real scenario, so it seems to me better to make this case injectable
> > > rather
> > > than EINVAL.
> > > 
> > > How about checking is_huge_zero_page() before try_to_split_thp_page()?
> > > The result should be consistent with the results when called by other
> > > memory_failure()'s callers  like MCE handler and
> > > hard_offline_page_store().
> > 
> > Agree. thanks!
> > 
> > > 
> > > diff --git a/mm/memory-failure.c b/mm/memory-failure.c
> > > index 9b76222ee237..771fb4fc626c 100644
> > > --- a/mm/memory-failure.c
> > > +++ b/mm/memory-failure.c
> > > @@ -1852,6 +1852,12 @@ int memory_failure(unsigned long pfn, int flags)
> > >       }
> > >       if (PageTransHuge(hpage)) {
> > > +        if (is_huge_zero_page(hpage)) {
> > > +            action_result(pfn, MF_MSG_KERNEL_HIGH_ORDER, MF_IGNORED);
> > 
> > Should we use MF_MSG_UNSPLIT_THP instead of MF_MSG_KERNEL_HIGH_ORDER?
> > 
> > And should we SetPageHasHWPoisoned(hpage) for huge zero page, since
> > TestSetPageHWPoison(p) is done in the early part of memory_failure().

Yeah, these could be possible.  I suggested them to get the same result
regardless of calling interfaces of memory_failure().  How huge_zero pages
should be handled is separate from the reported issue on VM_BUG_ON_PAGE(),
so it would require a separate patch (which updates MF_COUNT_INCREASED=true
case too).

Thanks,
Naoya Horiguchi

> 
> If so, we just need to add a one-line condition in
> try_to_split_thp_page().