Re: [v2 PATCH 3/3] mm: hwpoison: dump page for unhandlable page

[HORIGUCHI NAOYA(堀口 直也)]

On Fri, Aug 20, 2021 at 11:40:24AM -0700, Yang Shi wrote:
> On Thu, Aug 19, 2021 at 11:48 PM HORIGUCHI NAOYA(堀口　直也)
> <naoya.horiguchi@xxxxxxx> wrote:
> >
> > On Wed, Aug 18, 2021 at 10:41:16PM -0700, Yang Shi wrote:
> > > Currently just very simple message is shown for unhandlable page, e.g.
> > > non-LRU page, like:
> > > soft_offline: 0x1469f2: unknown non LRU page type 5ffff0000000000 ()
> > >
> > > It is not very helpful for further debug, calling dump_page() could show
> > > more useful information.
> > >
> > > Calling dump_page() in get_any_page() in order to not duplicate the call
> > > in a couple of different places.  It may be called with pcp disabled and
> > > holding memory hotplug lock, it should be not a big deal since hwpoison
> > > handler is not called very often.
> > >
> > > Suggested-by: Matthew Wilcox <willy@xxxxxxxxxxxxx>
> > > Cc: Naoya Horiguchi <naoya.horiguchi@xxxxxxx>
> > > Cc: Oscar Salvador <osalvador@xxxxxxx>
> > > Signed-off-by: Yang Shi <shy828301@xxxxxxxxx>
> > > ---
> > >  mm/memory-failure.c | 3 +++
> > >  1 file changed, 3 insertions(+)
> > >
> > > diff --git a/mm/memory-failure.c b/mm/memory-failure.c
> > > index 7cfa134b1370..60df8fcd0444 100644
> > > --- a/mm/memory-failure.c
> > > +++ b/mm/memory-failure.c
> > > @@ -1228,6 +1228,9 @@ static int get_any_page(struct page *p, unsigned long flags)
> > >               ret = -EIO;
> > >       }
> > >  out:
> > > +     if (ret == -EIO)
> > > +             dump_page(p, "hwpoison: unhandlable page");
> > > +
> >
> > I feel that 4 callers of get_hwpoison_page() are in the different context,
> > so it might be better to consider them separately to add dump_page() or not.
> > soft_offline_page() still prints out "%s: %#lx: unknown page type: %lx (%pGp)"
> 
> No strong opinion to keep or remove it.

Reading the explanation below, I think that calling dump_page() in the
original place is fine.  So let's remove "else if (ret == 0)" block in
soft_offline_page().

> 
> > message, which might be duplicate so this printk() may be dropped.
> > In memory_failure_hugetlb() and memory_failure(), we can call dump_page() after
> > action_result().  unpoison_memory() doesn't need dump_page() at all because
> > it's related to already hwpoisoned page.
> 
> I don't have a strong opinion either to have the dump_page() called
> either before action or after action, it just moves around the dumped
> page information around that printk.
> 
> For unpoison_memory(), I think it is harmless to have dump_page()
> called, right? If get_hwpoison_page() can't return -EIO, then the
> dump_page() won't be called at all, if it is possible then this is
> exactly why we call dump_page() to help debug.
> 
> So IMHO calling dump_page() in get_any_page when -EIO is returned
> could work for all the cases well and avoid duplicating the call.

Fair enough. So could you repost 3/3 with the above change in soft_offline_page()?

Thanks,
Naoya Horiguchi