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From:   Yang Shi <shy828301@gmail.com>
Date:   Tue, 8 Jun 2021 12:36:05 -0700
Message-ID: <CAHbLzkrQdt+gvq-SdQoH8sVVNiSxdMqreTGsrZC4AsVpYzysWQ@mail.gmail.com>
Subject: Re: [PATCH] mm: mempolicy: don't have to split pmd for huge zero page
To:     Michal Hocko <mhocko@suse.com>
Cc:     Zi Yan <ziy@nvidia.com>, nao.horiguchi@gmail.com,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        Hugh Dickins <hughd@google.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Linux MM <linux-mm@kvack.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
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On Tue, Jun 8, 2021 at 10:49 AM Michal Hocko <mhocko@suse.com> wrote:
>
> On Tue 08-06-21 10:15:36, Yang Shi wrote:
> [...]
> > I did some archeology, the findings are:
> >
> > The zero page has PageReserved flag set, it was skipped by the
> > explicit PageReserved check in mempolicy.c since commit f4598c8b3678
> > ("[PATCH] migration: make sure there is no attempt to migrate reserved
> > pages."). The zero page was not used anymore by do_anonymous_page()
> > since 2.6.24 by commit 557ed1fa2620 ("remove ZERO_PAGE"), then
> > reinstated by commit a13ea5b759645 ("mm: reinstate ZERO_PAGE") and
> > this commit added zero page check in vm_normal_page(), so mempolicy
> > doesn't depend on PageReserved check to skip zero page anymore since
> > then.
> >
> > So the zero page is skipped by mempolicy.c since 2.6.16.
>
> Thanks a lot! This is really useful. Can you just add it to the
> changelog so others do not have to go through the painful archeology.
>
> With that, feel free to add
> Acked-by: Michal Hocko <mhocko@suse.com>

Thanks. Will add that into v2.

>
> Thanls!
> --
> Michal Hocko
> SUSE Labs