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From: Wei Yang <richard.weiyang@linux.alibaba.com>
To: David Hildenbrand <david@redhat.com>
Cc: Wei Yang <richard.weiyang@gmail.com>,
	Wei Yang <richard.weiyang@linux.alibaba.com>,
	linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	Michal Hocko <mhocko@suse.com>,
	stable@vger.kernel.org, Andrew Morton <akpm@linux-foundation.org>,
	Johannes Weiner <hannes@cmpxchg.org>,
	Minchan Kim <minchan@kernel.org>,
	Huang Ying <ying.huang@intel.com>,
	Mel Gorman <mgorman@techsingularity.net>,
	Dan Williams <dan.j.williams@intel.com>
Subject: Re: [PATCH v2 1/3] mm/shuffle: don't move pages between zones and don't read garbage memmaps
Date: Tue, 23 Jun 2020 17:30:18 +0800	[thread overview]
Message-ID: <20200623093018.GA6069@L-31X9LVDL-1304.local> (raw)
In-Reply-To: <c0b62330-11d3-e628-a811-b54789d8f182@redhat.com>

On Tue, Jun 23, 2020 at 09:55:43AM +0200, David Hildenbrand wrote:
>On 23.06.20 09:39, David Hildenbrand wrote:
>>> Hmm.. I thought this is the behavior for early section, while it looks current
>>> code doesn't work like this:
>>>
>>>        if (section_is_early && memmap)
>>>                free_map_bootmem(memmap);
>>>        else
>>> 	       depopulate_section_memmap(pfn, nr_pages, altmap);
>>>
>>> section_is_early is always "true" for early section, while memmap is not-NULL
>>> only when sub-section map is empty.
>>>
>>> If my understanding is correct, when we remove a sub-section in early section,
>>> the code would call depopulate_section_memmap(), which in turn free related
>>> memmap. By removing the memmap, the return value from pfn_to_online_page() is
>>> not a valid one.
>> 
>> I think you're right, and pfn_valid() would also return true, as it is
>> an early section. This looks broken.
>> 
>>>
>>> Maybe we want to write the code like this:
>>>
>>>        if (section_is_early)
>>>                if (memmap)
>>>                        free_map_bootmem(memmap);
>>>        else
>>> 	       depopulate_section_memmap(pfn, nr_pages, altmap);
>>>
>> 
>> I guess that should be the way to go
>> 
>> @Dan, I think what Wei proposes here is correct, right? Or how does it
>> work in the VMEMMAP case with early sections?
>> 
>
>Especially, if you would re-hot-add, section_activate() would assume
>there is a memmap, it must not be removed.
>

You are right here. I didn't notice it.

>@Wei, can you send a patch?
>

Sure, let me prepare for it.

>-- 
>Thanks,
>
>David / dhildenb

-- 
Wei Yang
Help you, Help me


  reply	other threads:[~2020-06-23  9:30 UTC|newest]

Thread overview: 30+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-06-19 12:59 [PATCH v2 0/3] mm/shuffle: fix and cleanups David Hildenbrand
2020-06-19 12:59 ` [PATCH v2 1/3] mm/shuffle: don't move pages between zones and don't read garbage memmaps David Hildenbrand
2020-06-20  1:37   ` Williams, Dan J
2020-06-22  8:26   ` Wei Yang
2020-06-22  8:43     ` David Hildenbrand
2020-06-22  9:22       ` Wei Yang
2020-06-22  9:51         ` David Hildenbrand
2020-06-22 13:10           ` Wei Yang
2020-06-22 14:06             ` David Hildenbrand
2020-06-22 21:55               ` Wei Yang
2020-06-23  7:39                 ` David Hildenbrand
2020-06-23  7:55                   ` David Hildenbrand
2020-06-23  9:30                     ` Wei Yang [this message]
2020-07-24  3:08                       ` Andrew Morton
2020-07-24  5:45                         ` Wei Yang
2020-07-24  8:20                         ` David Hildenbrand
2020-06-22 14:11         ` David Hildenbrand
2020-06-19 12:59 ` [PATCH v2 2/3] mm/memory_hotplug: document why shuffle_zone() is relevant David Hildenbrand
2020-06-20  1:41   ` Dan Williams
2020-06-22  7:27     ` David Hildenbrand
2020-06-23 21:15       ` Dan Williams
2020-06-24  9:31         ` David Hildenbrand
2020-06-22 15:32   ` Michal Hocko
2020-06-19 12:59 ` [PATCH v2 3/3] mm/shuffle: remove dynamic reconfiguration David Hildenbrand
2020-06-20  1:49   ` Dan Williams
2020-06-22  7:33     ` David Hildenbrand
2020-06-22  8:37       ` Wei Yang
2020-06-23 22:18       ` Dan Williams
2020-06-22 15:37   ` Michal Hocko
2020-06-23  1:22   ` Wei Yang

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