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From:   Alexander Duyck <alexander.duyck@gmail.com>
Date:   Mon, 9 Aug 2021 07:12:04 -0700
Message-ID: <CAKgT0UdCVTYiiGHuhBv7VnyJeD3ZAijBcZPLEPc=r7QD=9veNA@mail.gmail.com>
Subject: Re: [RFC PATCH 11/15] mm/page_reporting: report pages at section size
 instead of MAX_ORDER.
To:     David Hildenbrand <david@redhat.com>
Cc:     Zi Yan <ziy@nvidia.com>, linux-mm <linux-mm@kvack.org>,
        Matthew Wilcox <willy@infradead.org>,
        Vlastimil Babka <vbabka@suse.cz>,
        "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
        Mike Kravetz <mike.kravetz@oracle.com>,
        Michal Hocko <mhocko@kernel.org>,
        John Hubbard <jhubbard@nvidia.com>,
        LKML <linux-kernel@vger.kernel.org>
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On Mon, Aug 9, 2021 at 12:25 AM David Hildenbrand <david@redhat.com> wrote:
>
> On 05.08.21 21:02, Zi Yan wrote:
> > From: Zi Yan <ziy@nvidia.com>
> >
> > page_reporting_order was set to MAX_ORDER, which is always smaller than
> > a memory section size. An upcoming change will make MAX_ORDER larger
> > than a memory section size. Set page_reporting_order to
> > PFN_SECTION_SHIFT to match existing size assumption.
> >
> > Signed-off-by: Zi Yan <ziy@nvidia.com>
> > Cc: David Hildenbrand <david@redhat.com>
> > Cc: linux-mm@kvack.org
> > Cc: linux-kernel@vger.kernel.org
> > ---
> >   mm/page_reporting.c | 3 ++-
> >   1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/mm/page_reporting.c b/mm/page_reporting.c
> > index 382958eef8a9..dc4a2d699862 100644
> > --- a/mm/page_reporting.c
> > +++ b/mm/page_reporting.c
> > @@ -11,7 +11,8 @@
> >   #include "page_reporting.h"
> >   #include "internal.h"
> >
> > -unsigned int page_reporting_order = MAX_ORDER;
> > +/* Set page_reporting_order at section size */
> > +unsigned int page_reporting_order = PFN_SECTION_SHIFT;
> >   module_param(page_reporting_order, uint, 0644);
> >   MODULE_PARM_DESC(page_reporting_order, "Set page reporting order");
> >
> >
>
> If you look closely, this is only a placeholder and will get overwritten
> in page_reporting_register(). I don't recall why we have the module
> parameter at all. Most probably, to adjust the reporting order after we
> already registered a user. Can't we just initialize that to 0 ?

Yeah, it is pretty much there for debugging in the event that we are
on an architecture that is misconfigured.