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

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Date:   Mon, 9 Aug 2021 09:25:26 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Zi Yan <ziy@...dia.com>, linux-mm@...ck.org,
        Alexander Duyck <alexander.duyck@...il.com>
Cc:     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>,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 11/15] mm/page_reporting: report pages at section size
 instead of MAX_ORDER.

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 ?

-- 
Thanks,

David / dhildenb