linux-kernel - Re: [RFC PATCH 11/15] mm/page_reporting: report pages at section size instead of MAX

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Date:   Mon, 09 Aug 2021 11:08:09 -0400
From:   Zi Yan <ziy@...dia.com>
To:     Alexander Duyck <alexander.duyck@...il.com>
Cc:     David Hildenbrand <david@...hat.com>,
        linux-mm <linux-mm@...ck.org>,
        Matthew Wilcox <willy@...radead.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Michal Hocko <mhocko@...nel.org>,
        John Hubbard <jhubbard@...dia.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH 11/15] mm/page_reporting: report pages at section size instead of MAX_ORDER.

On 9 Aug 2021, at 10:12, Alexander Duyck wrote:

> On Mon, Aug 9, 2021 at 12:25 AM David Hildenbrand <david@...hat.com> wrote:
>>
>> On 05.08.21 21:02, Zi Yan wrote:
>>> From: Zi Yan <ziy@...dia.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@...dia.com>
>>> Cc: David Hildenbrand <david@...hat.com>
>>> Cc: linux-mm@...ck.org
>>> Cc: linux-kernel@...r.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.

MAX_ORDER is changed to a boot time variable in Patch 15, thus cannot be used
for page_reporting_order initialization after that.

Thanks for David’s explanation. I will initialize page_reporting_order to 0
and fix the commit message.

—
Best Regards,
Yan, Zi

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