linux-kernel - Re: [PATCH -next] mm/hotplug: skip bad PFNs from pfn_to_online

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Date:   Fri, 14 Jun 2019 10:59:25 -0400
From:   Qian Cai <cai@....pw>
To:     "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>,
        Dan Williams <dan.j.williams@...el.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Oscar Salvador <osalvador@...e.de>,
        Linux MM <linux-mm@...ck.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH -next] mm/hotplug: skip bad PFNs from
 pfn_to_online_page()

On Fri, 2019-06-14 at 14:28 +0530, Aneesh Kumar K.V wrote:
> Qian Cai <cai@....pw> writes:
> 
> 
> > 1) offline is busted [1]. It looks like test_pages_in_a_zone() missed the
> > same
> > pfn_section_valid() check.
> > 
> > 2) powerpc booting is generating endless warnings [2]. In
> > vmemmap_populated() at
> > arch/powerpc/mm/init_64.c, I tried to change PAGES_PER_SECTION to
> > PAGES_PER_SUBSECTION, but it alone seems not enough.
> > 
> 
> Can you check with this change on ppc64.  I haven't reviewed this series yet.
> I did limited testing with change . Before merging this I need to go
> through the full series again. The vmemmap poplulate on ppc64 needs to
> handle two translation mode (hash and radix). With respect to vmemap
> hash doesn't setup a translation in the linux page table. Hence we need
> to make sure we don't try to setup a mapping for a range which is
> arleady convered by an existing mapping.

It works fine.

> 
> diff --git a/arch/powerpc/mm/init_64.c b/arch/powerpc/mm/init_64.c
> index a4e17a979e45..15c342f0a543 100644
> --- a/arch/powerpc/mm/init_64.c
> +++ b/arch/powerpc/mm/init_64.c
> @@ -88,16 +88,23 @@ static unsigned long __meminit
> vmemmap_section_start(unsigned long page)
>   * which overlaps this vmemmap page is initialised then this page is
>   * initialised already.
>   */
> -static int __meminit vmemmap_populated(unsigned long start, int page_size)
> +static bool __meminit vmemmap_populated(unsigned long start, int page_size)
>  {
>  	unsigned long end = start + page_size;
>  	start = (unsigned long)(pfn_to_page(vmemmap_section_start(start)));
>  
> -	for (; start < end; start += (PAGES_PER_SECTION * sizeof(struct
> page)))
> -		if (pfn_valid(page_to_pfn((struct page *)start)))
> -			return 1;
> +	for (; start < end; start += (PAGES_PER_SECTION * sizeof(struct
> page))) {
>  
> -	return 0;
> +		struct mem_section *ms;
> +		unsigned long pfn = page_to_pfn((struct page *)start);
> +
> +		if (pfn_to_section_nr(pfn) >= NR_MEM_SECTIONS)
> +			return 0;
> +		ms = __nr_to_section(pfn_to_section_nr(pfn));
> +		if (valid_section(ms))
> +			return true;
> +	}
> +	return false;
>  }
>  
>  /*
>