From: David Hildenbrand <david@redhat.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"linux-mm@kvack.org" <linux-mm@kvack.org>,
Michal Hocko <mhocko@kernel.org>
Subject: Re: [PATCH v2 2/2] mm/memory-failure.c: Don't access uninitialized memmaps in memory_failure()
Date: Mon, 21 Oct 2019 11:44:19 +0200 [thread overview]
Message-ID: <15e0a869-4edf-a5c4-64b1-5ed25a6ff720@redhat.com> (raw)
In-Reply-To: <20191018190531.975b70fabdce5f7e5d6b27df@linux-foundation.org>
On 19.10.19 04:05, Andrew Morton wrote:
> On Thu, 10 Oct 2019 09:17:42 +0200 David Hildenbrand <david@redhat.com> wrote:
>
>>>> - pgmap = get_dev_pagemap(pfn, NULL);
>>>> - if (pgmap)
>>>> - return memory_failure_dev_pagemap(pfn, flags, pgmap);
>>>> -
>>>> - p = pfn_to_page(pfn);
>>>
>>> This change seems to assume that memory_failure_dev_pagemap() is never
>>> called for online pages. Is it an intended behavior?
>>> Or the concept "online pages" is not applicable to zone device pages?
>>
>> Yes, that's the real culprit. ZONE_DEVICE/devmem pages are never online
>> (SECTION_IS_ONLINE). The terminology "online" only applies to pages that
>> were given to the buddy. And as we support sup-section hotadd for
>> devmem, we cannot easily make use of the section flag it. I already
>> proposed somewhere to convert SECTION_IS_ONLINE to a subsection bitmap
>> and call it something like pfn_active().
>>
>> pfn_online() would then be "pfn_active() && zone != ZONE_DEVICE". And we
>> could use pfn_active() everywhere to test for initialized memmaps (well,
>> besides some special cases like device reserved memory that does not
>> span full sub-sections). Until now, nobody volunteered and I have other
>> things to do.
>
> Is it worth a code comment or two to make this clearer?
You mean something like
/* Only pages managed by the buddy are online (not ZONE_DEVICE). */
?
--
Thanks,
David / dhildenb
next prev parent reply other threads:[~2019-10-21 9:44 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-09 14:24 [PATCH v2 0/2] mm: Don't access uninitialized memmaps in PFN walkers David Hildenbrand
2019-10-09 14:24 ` [PATCH v2 1/2] mm: Don't access uninitialized memmaps in fs/proc/page.c David Hildenbrand
2019-10-09 14:41 ` Michal Hocko
2019-10-14 8:44 ` David Hildenbrand
2019-10-09 14:24 ` [PATCH v2 2/2] mm/memory-failure.c: Don't access uninitialized memmaps in memory_failure() David Hildenbrand
2019-10-09 14:43 ` Michal Hocko
2019-10-10 7:27 ` David Hildenbrand
2019-10-10 7:35 ` Michal Hocko
2019-10-10 7:52 ` David Hildenbrand
2019-10-10 7:58 ` David Hildenbrand
2019-10-11 6:02 ` Naoya Horiguchi
2019-10-11 10:13 ` David Hildenbrand
2019-10-14 13:36 ` Michal Hocko
2019-10-15 14:23 ` Oscar Salvador
2019-10-10 0:26 ` Naoya Horiguchi
2019-10-10 7:17 ` David Hildenbrand
2019-10-11 6:50 ` Naoya Horiguchi
2019-10-19 2:05 ` Andrew Morton
2019-10-21 9:44 ` David Hildenbrand [this message]
2019-10-14 8:41 ` David Hildenbrand
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