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Date:   Thu, 6 Feb 2020 14:15:35 +0000
From:   Wei Yang <richard.weiyang@gmail.com>
To:     Baoquan He <bhe@redhat.com>
Cc:     David Hildenbrand <david@redhat.com>,
        Wei Yang <richardw.yang@linux.intel.com>,
        akpm@linux-foundation.org, osalvador@suse.de,
        dan.j.williams@intel.com, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH] mm/sparsemem: pfn_to_page is not valid yet on SPARSEMEM
Message-ID: <20200206141535.4w4h5wnuzxmi37wu@master>
Reply-To: Wei Yang <richard.weiyang@gmail.com>
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On Thu, Feb 06, 2020 at 09:50:16PM +0800, Baoquan He wrote:
>On 02/06/20 at 02:28pm, David Hildenbrand wrote:
>> On 06.02.20 13:53, Wei Yang wrote:
>> > When we use SPARSEMEM instead of SPARSEMEM_VMEMMAP, pfn_to_page()
>> > doesn't work before sparse_init_one_section() is called. This leads to a
>> > crash when hotplug memory.
>> > 
>> > We should use memmap as it did.
>> > 
>> > Fixes: ba72b4c8cf60 ("mm/sparsemem: support sub-section hotplug")
>> > Signed-off-by: Wei Yang <richardw.yang@linux.intel.com>
>> > CC: Dan Williams <dan.j.williams@intel.com>
>> > ---
>> >  mm/sparse.c | 2 +-
>> >  1 file changed, 1 insertion(+), 1 deletion(-)
>> > 
>> > diff --git a/mm/sparse.c b/mm/sparse.c
>> > index 5a8599041a2a..2efb24ff8f96 100644
>> > --- a/mm/sparse.c
>> > +++ b/mm/sparse.c
>> > @@ -882,7 +882,7 @@ int __meminit sparse_add_section(int nid, unsigned long start_pfn,
>> >  	 * Poison uninitialized struct pages in order to catch invalid flags
>> >  	 * combinations.
>> >  	 */
>> > -	page_init_poison(pfn_to_page(start_pfn), sizeof(struct page) * nr_pages);
>> > +	page_init_poison(memmap, sizeof(struct page) * nr_pages);
>> 
>> If you add sub-sections that don't fall onto the start of the section,
>> 
>> pfn_to_page(start_pfn) != memmap
>> 
>> and your patch would break that under SPARSEMEM_VMEMMAP if I am not wrong.
>
>It returns the pfn_to_page(pfn) from __populate_section_memmap() and
>assign to memmap in vmemmap case, how come it breaks anything. Correct
>me if I was wrong.
>

Just see your reply.

Thanks for your explanation. :-)

>> David / dhildenb

-- 
Wei Yang
Help you, Help me