linux-kernel - Re: [PATCH -rc7] mm/huge_memory: mark huge_zero

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Date: Tue, 14 May 2024 14:42:04 -0700
From: Andrew Morton <akpm@...ux-foundation.org>
To: Yang Shi <shy828301@...il.com>
Cc: Miaohe Lin <linmiaohe@...wei.com>, nao.horiguchi@...il.com,
 xuyu@...ux.alibaba.com, linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH -rc7] mm/huge_memory: mark huge_zero_page reserved

On Tue, 14 May 2024 15:28:12 -0600 Yang Shi <shy828301@...il.com> wrote:

> On Tue, May 14, 2024 at 3:14 PM Andrew Morton <akpm@...ux-foundation.org> wrote:
> >
> > On Sat, 11 May 2024 11:54:35 +0800 Miaohe Lin <linmiaohe@...wei.com> wrote:
> >
> > > When I did memory failure tests recently, below panic occurs:
> > >
> > >  kernel BUG at include/linux/mm.h:1135!
> > >  invalid opcode: 0000 [#1] PREEMPT SMP NOPTI
> > >  CPU: 9 PID: 137 Comm: kswapd1 Not tainted 6.9.0-rc4-00491-gd5ce28f156fe-dirty #14
> > >
> > > ...
> > >
> > > --- a/mm/huge_memory.c
> > > +++ b/mm/huge_memory.c
> > > @@ -208,6 +208,7 @@ static bool get_huge_zero_page(void)
> > >               __free_pages(zero_page, compound_order(zero_page));
> > >               goto retry;
> > >       }
> > > +     __SetPageReserved(zero_page);
> > >       WRITE_ONCE(huge_zero_pfn, page_to_pfn(zero_page));
> > >
> > >       /* We take additional reference here. It will be put back by shrinker */
> > > @@ -260,6 +261,7 @@ static unsigned long shrink_huge_zero_page_scan(struct shrinker *shrink,
> > >               struct page *zero_page = xchg(&huge_zero_page, NULL);
> > >               BUG_ON(zero_page == NULL);
> > >               WRITE_ONCE(huge_zero_pfn, ~0UL);
> > > +             __ClearPageReserved(zero_page);
> > >               __free_pages(zero_page, compound_order(zero_page));
> > >               return HPAGE_PMD_NR;
> > >       }
> >
> > This causes a bit of a mess when staged ahead of mm-stable.  So to
> > avoid disruption I staged it behind mm-stable.  This means that when
> > the -stable maintainers try to merge it, they will ask for a fixed up
> > version for older kernels so you can please just send them this
> > version.
> 
> Can you please drop this from mm-unstable since both I and David
> nack'ed a similar patch in another thread.
> https://lore.kernel.org/linux-mm/20240511032801.1295023-1-linmiaohe@huawei.com/

That appears to link to the incorrect email thread?