From: David Hildenbrand <david@redhat.com>
To: Toshiki Fukasawa <t-fukasawa@vx.jp.nec.com>,
"linux-mm@kvack.org" <linux-mm@kvack.org>,
"dan.j.williams@intel.com" <dan.j.williams@intel.com>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"akpm@linux-foundation.org" <akpm@linux-foundation.org>,
"mhocko@kernel.org" <mhocko@kernel.org>,
"adobriyan@gmail.com" <adobriyan@gmail.com>,
"hch@lst.de" <hch@lst.de>,
"longman@redhat.com" <longman@redhat.com>,
"sfr@canb.auug.org.au" <sfr@canb.auug.org.au>,
"mst@redhat.com" <mst@redhat.com>,
Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>,
Junichi Nomura <j-nomura@ce.jp.nec.com>
Subject: Re: [RFC PATCH v2] mm: initialize struct pages reserved by ZONE_DEVICE driver.
Date: Tue, 17 Sep 2019 09:13:10 +0200 [thread overview]
Message-ID: <38e58d23-c20b-4e68-5f56-20bba2be2d6c@redhat.com> (raw)
In-Reply-To: <31fd3c86-5852-1863-93bd-8df9da9f95b4@vx.jp.nec.com>
On 17.09.19 04:34, Toshiki Fukasawa wrote:
> On 2019/09/09 16:46, David Hildenbrand wrote:
>> Let's take a step back here to understand the issues I am aware of. I
>> think we should solve this for good now:
>>
>> A PFN walker takes a look at a random PFN at a random point in time. It
>> finds a PFN with SECTION_MARKED_PRESENT && !SECTION_IS_ONLINE. The
>> options are:
>>
>> 1. It is buddy memory (add_memory()) that has not been online yet. The
>> memmap contains garbage. Don't access.
>>
>> 2. It is ZONE_DEVICE memory with a valid memmap. Access it.
>>
>> 3. It is ZONE_DEVICE memory with an invalid memmap, because the section
>> is only partially present: E.g., device starts at offset 64MB within a
>> section or the device ends at offset 64MB within a section. Don't access it.
>
> I don't agree with case #3. In the case, struct page area is not allocated on
> ZONE_DEVICE, but is allocated on system memory. So I think we can access the
> struct pages. What do you mean "invalid memmap"?
No, that's not the case. There is no memory, especially not system
memory. We only allow partially present sections (sub-section memory
hotplug) for ZONE_DEVICE.
invalid memmap == memmap was not initialized == struct pages contains
garbage. There is a memmap, but accessing it (e.g., pfn_to_nid()) will
trigger a BUG.
--
Thanks,
David / dhildenb
next prev parent reply other threads:[~2019-09-17 7:13 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-09-06 8:09 [RFC PATCH v2] mm: initialize struct pages reserved by ZONE_DEVICE driver Toshiki Fukasawa
2019-09-06 8:45 ` David Hildenbrand
2019-09-06 10:02 ` Toshiki Fukasawa
2019-09-06 10:35 ` David Hildenbrand
2019-09-09 5:48 ` Toshiki Fukasawa
2019-09-09 7:46 ` David Hildenbrand
2019-09-09 8:10 ` David Hildenbrand
2019-09-09 11:53 ` Dan Williams
2019-09-09 12:05 ` David Hildenbrand
2019-09-10 9:21 ` Dan Williams
2019-09-10 10:10 ` David Hildenbrand
2019-09-17 2:34 ` Toshiki Fukasawa
2019-09-17 7:13 ` David Hildenbrand [this message]
2019-09-17 9:32 ` Toshiki Fukasawa
2019-09-17 10:20 ` David Hildenbrand
2019-09-18 2:16 ` Toshiki Fukasawa
2019-09-17 15:49 ` Waiman Long
2019-09-17 16:21 ` Qian Cai
2019-09-17 17:04 ` Waiman Long
2019-09-17 20:23 ` David Hildenbrand
2019-09-18 2:28 ` Toshiki Fukasawa
2019-09-18 7:30 ` David Hildenbrand
2019-09-10 14:01 ` Michal Hocko
2019-09-10 14:53 ` Dan Williams
2019-09-10 17:35 ` Michal Hocko
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