linux-kernel - Re: [PATCH v1 1/4] resource: Use PFN_UP / PFN_DOWN in walk_system_ram

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Date:   Wed, 14 Aug 2019 16:06:08 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     David Hildenbrand <david@...hat.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Dan Williams <dan.j.williams@...el.com>,
        Borislav Petkov <bp@...e.de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Ingo Molnar <mingo@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Nadav Amit <namit@...are.com>,
        Wei Yang <richardw.yang@...ux.intel.com>,
        Oscar Salvador <osalvador@...e.de>
Subject: Re: [PATCH v1 1/4] resource: Use PFN_UP / PFN_DOWN in
 walk_system_ram_range()

On Fri 09-08-19 14:56:58, David Hildenbrand wrote:
> This makes it clearer that we will never call func() with duplicate PFNs
> in case we have multiple sub-page memory resources. All unaligned parts
> of PFNs are completely discarded.
> 
> Cc: Dan Williams <dan.j.williams@...el.com>
> Cc: Borislav Petkov <bp@...e.de>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Bjorn Helgaas <bhelgaas@...gle.com>
> Cc: Ingo Molnar <mingo@...nel.org>
> Cc: Dave Hansen <dave.hansen@...ux.intel.com>
> Cc: Nadav Amit <namit@...are.com>
> Cc: Wei Yang <richardw.yang@...ux.intel.com>
> Cc: Oscar Salvador <osalvador@...e.de>
> Signed-off-by: David Hildenbrand <david@...hat.com>

Acked-by: Michal Hocko <mhocko@...e.com>

> ---
>  kernel/resource.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/resource.c b/kernel/resource.c
> index 7ea4306503c5..88ee39fa9103 100644
> --- a/kernel/resource.c
> +++ b/kernel/resource.c
> @@ -487,8 +487,8 @@ int walk_system_ram_range(unsigned long start_pfn, unsigned long nr_pages,
>  	while (start < end &&
>  	       !find_next_iomem_res(start, end, flags, IORES_DESC_NONE,
>  				    false, &res)) {
> -		pfn = (res.start + PAGE_SIZE - 1) >> PAGE_SHIFT;
> -		end_pfn = (res.end + 1) >> PAGE_SHIFT;
> +		pfn = PFN_UP(res.start);
> +		end_pfn = PFN_DOWN(res.end + 1);
>  		if (end_pfn > pfn)
>  			ret = (*func)(pfn, end_pfn - pfn, arg);
>  		if (ret)
> -- 
> 2.21.0

-- 
Michal Hocko
SUSE Labs