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

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Date:   Fri, 20 Aug 2021 11:40:24 -0700
From:   Yang Shi <shy828301@...il.com>
To:     HORIGUCHI NAOYA(堀口 直也) 
        <naoya.horiguchi@....com>
Cc:     "osalvador@...e.de" <osalvador@...e.de>,
        "tdmackey@...tter.com" <tdmackey@...tter.com>,
        "david@...hat.com" <david@...hat.com>,
        "willy@...radead.org" <willy@...radead.org>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "corbet@....net" <corbet@....net>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [v2 PATCH 3/3] mm: hwpoison: dump page for unhandlable page

On Thu, Aug 19, 2021 at 11:48 PM HORIGUCHI NAOYA(堀口　直也)
<naoya.horiguchi@....com> 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@...radead.org>
> > Cc: Naoya Horiguchi <naoya.horiguchi@....com>
> > Cc: Oscar Salvador <osalvador@...e.de>
> > Signed-off-by: Yang Shi <shy828301@...il.com>
> > ---
> >  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.

> 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.

>
> Thanks,
> Naoya Horiguchi