From: David Hildenbrand <david@redhat.com>
To: Pingfan Liu <kernelfans@gmail.com>, Michal Hocko <mhocko@suse.com>
Cc: Dan Williams <dan.j.williams@intel.com>,
Linux-MM <linux-mm@kvack.org>,
Andrew Morton <akpm@linux-foundation.org>,
Oscar Salvador <osalvador@suse.de>,
Kexec Mailing List <kexec@lists.infradead.org>,
Kazuhito Hagio <k-hagio@ab.jp.nec.com>
Subject: Re: [PATCH] mm/sparse: reset section's mem_map when fully deactivated
Date: Fri, 17 Jan 2020 10:52:54 +0100 [thread overview]
Message-ID: <e81efb3d-254b-9858-443e-234d427d5ab8@redhat.com> (raw)
In-Reply-To: <CAFgQCTsT0dFEOn75XoJf-KUApy+Mz7wDSoZsdd=GwkbGFPu-Bw@mail.gmail.com>
On 17.01.20 10:49, Pingfan Liu wrote:
> On Fri, Jan 17, 2020 at 3:47 PM Michal Hocko <mhocko@suse.com> wrote:
>>
>> On Thu 16-01-20 23:14:02, Dan Williams wrote:
>>> On Thu, Jan 16, 2020 at 10:23 PM Pingfan Liu <kernelfans@gmail.com> wrote:
>>>>
>>>> On Thu, Jan 16, 2020 at 3:50 PM Michal Hocko <mhocko@suse.com> wrote:
>>>>>
>>>>> On Thu 16-01-20 11:01:08, Pingfan Liu wrote:
>>>>>> When fully deactivated, it is meaningless to keep the value of a section's
>>>>>> mem_map. And its mem_map will be reassigned during re-added.
>>>>>>
>>>>>> Beside this, it breaks the user space tool "makedumpfile", which makes
>>>>>> assumption that a hot-removed section having mem_map as NULL.
>>>>>
>>>>> We used to do that before ba72b4c8cf60 ("mm/sparsemem: support
>>>>> sub-section hotplug"). Dan was this an intentional change?
>>>> I do not know the purpose of this. But the change just leave section
>>>> start pfn in fully deactivated section_mem_map, and not used any more.
>>>
>>> Not intentional, IIRC at the time I had convinced myself that the
>>> value would always be translated by sparse_decode_mem_map(), so I
>>> thought it could be hiding NULL de-references. I don't see any harm
>>> in the patch.
>>
>> Thanks for the confirmation. It would be great to have this in the
>> changelog.
> Should I post V2 with this commit log?
>
> Thanks,
> Pingfan
>
Id' say yes, and maybe also add some details why this makes makedumpfile
bail out now, so people looking at this commit only know what's happening.
--
Thanks,
David / dhildenb
next prev parent reply other threads:[~2020-01-17 9:53 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-16 3:01 Pingfan Liu
2020-01-16 3:18 ` Qian Cai
2020-01-16 3:34 ` Pingfan Liu
2020-01-16 7:50 ` Michal Hocko
2020-01-17 6:22 ` Pingfan Liu
2020-01-17 7:14 ` Dan Williams
2020-01-17 7:47 ` Michal Hocko
2020-01-17 9:49 ` Pingfan Liu
2020-01-17 9:52 ` David Hildenbrand [this message]
2020-01-20 2:31 ` Pingfan Liu
2020-01-16 8:06 ` David Hildenbrand
2020-01-16 8:14 ` David Hildenbrand
2020-01-16 8:24 ` Baoquan He
2020-01-16 8:57 ` David Hildenbrand
2020-01-17 6:20 ` Pingfan Liu
2020-01-17 6:18 ` Pingfan Liu
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