From: David Hildenbrand <david@redhat.com>
To: Michal Hocko <mhocko@suse.com>
Cc: Oscar Salvador <osalvador@suse.de>,
Andrew Morton <akpm@linux-foundation.org>,
Anshuman Khandual <anshuman.khandual@arm.com>,
Vlastimil Babka <vbabka@suse.cz>,
Pavel Tatashin <pasha.tatashin@soleen.com>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v5 1/5] mm,memory_hotplug: Allocate memmap from the added memory range
Date: Thu, 25 Mar 2021 16:19:36 +0100 [thread overview]
Message-ID: <40fac999-2d28-9205-23f0-516fa9342bbe@redhat.com> (raw)
In-Reply-To: <YFyoU/rkEPK3VPlN@dhcp22.suse.cz>
On 25.03.21 16:12, Michal Hocko wrote:
> On Thu 25-03-21 15:46:22, David Hildenbrand wrote:
>> On 25.03.21 15:34, Michal Hocko wrote:
>>> On Thu 25-03-21 15:09:35, David Hildenbrand wrote:
>>>> On 25.03.21 15:08, Michal Hocko wrote:
>>>>> On Thu 25-03-21 13:40:45, David Hildenbrand wrote:
>>>>>> On 25.03.21 13:35, Michal Hocko wrote:
>>>>>>> On Thu 25-03-21 12:08:43, David Hildenbrand wrote:
>>>>>>>> On 25.03.21 11:55, Oscar Salvador wrote:
>>>>> [...]
>>>>>>>>> - When moving the initialization/accounting to hot-add/hot-remove,
>>>>>>>>> the section containing the vmemmap pages will remain offline.
>>>>>>>>> It might get onlined once the pages get online in online_pages(),
>>>>>>>>> or not if vmemmap pages span a whole section.
>>>>>>>>> I remember (but maybe David rmemeber better) that that was a problem
>>>>>>>>> wrt. pfn_to_online_page() and hybernation/kdump.
>>>>>>>>> So, if that is really a problem, we would have to care of ot setting
>>>>>>>>> the section to the right state.
>>>>>>>>
>>>>>>>> Good memory. Indeed, hibernation/kdump won't save the state of the vmemmap,
>>>>>>>> because the memory is marked as offline and, thus, logically without any
>>>>>>>> valuable content.
>>>
>>> ^^^^ THIS
>>>
>>>>>>>
>>>>>>> Could you point me to the respective hibernation code please? I always
>>>>>>> get lost in that area. Anyway, we do have the same problem even if the
>>>>>>> whole accounting is handled during {on,off}lining, no?
>>>>>>
>>>>>> kernel/power/snapshot.c:saveable_page().
>>>>>
>>>>> Thanks! So this is as I've suspected. The very same problem is present
>>>>> if the memory block is marked offline. So we need a solution here
>>>>> anyway. One way to go would be to consider these vmemmap pages always
>>>>> online. pfn_to_online_page would have to special case them but we would
>>>>> need to identify them first. I used to have PageVmemmap or something
>>>>> like that in my early attempt to do this.
>>>>>
>>>>> That being said this is not an argument for one or the other aproach.
>>>>> Both need fixing.
>>>>
>>>> Can you elaborate? What is the issue there? What needs fixing?
>>>
>>> offline section containing vmemmap will be lost during hibernation cycle
>>> IIU the above correctly.
>>>
>>
>> Can tell me how that is a problem with Oscars current patch? I only see this
>> being a problem with what you propose - most probably I am missing something
>> important here.
>>
>> Offline memory sections don't have a valid memmap (assumption: garbage). On
>> hibernation, the whole offline memory block won't be saved, including the
>> vmemmap content that resides on the block. This includes the vmemmap of the
>> vmemmap pages, which is itself.
>>
>> When restoring, the whole memory block will contain garbage, including the
>> whole vmemmap - which is marked to be offline and to contain garbage.
>
> Hmm, so I might be misunderstanding the restoring part. But doesn't that
> mean that the whole section/memory block won't get restored because it
> is offline and therefore the vmemmap would be pointing to nowhere?
AFAIU, only the content of the memory block won't be restored - whatever
memory content existed before the restore operation is kept.
The structures that define how the vmemmap should look like - the memory
sections and the page tables used for describing the vmemmap should
properly get saved+restored, as these are located on online memory.
So the vmemmap layout should look after restoring just like before saving.
--
Thanks,
David / dhildenb
next prev parent reply other threads:[~2021-03-25 15:20 UTC|newest]
Thread overview: 63+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-19 9:26 [PATCH v5 0/5] Allocate memmap from hotadded memory (per device) Oscar Salvador
2021-03-19 9:26 ` [PATCH v5 1/5] mm,memory_hotplug: Allocate memmap from the added memory range Oscar Salvador
2021-03-19 10:20 ` David Hildenbrand
2021-03-19 10:31 ` Oscar Salvador
2021-03-19 12:04 ` David Hildenbrand
2021-03-23 10:11 ` Michal Hocko
2021-03-24 10:12 ` Oscar Salvador
2021-03-24 12:03 ` Michal Hocko
2021-03-24 12:10 ` Michal Hocko
2021-03-24 12:23 ` David Hildenbrand
2021-03-24 12:37 ` Michal Hocko
2021-03-24 13:13 ` David Hildenbrand
2021-03-24 13:40 ` Michal Hocko
2021-03-24 14:05 ` David Hildenbrand
2021-03-24 13:27 ` Oscar Salvador
2021-03-24 14:42 ` Michal Hocko
2021-03-24 14:52 ` David Hildenbrand
2021-03-24 16:04 ` Michal Hocko
2021-03-24 19:16 ` David Hildenbrand
2021-03-25 8:07 ` Oscar Salvador
2021-03-25 9:17 ` Michal Hocko
2021-03-25 10:55 ` Oscar Salvador
2021-03-25 11:08 ` David Hildenbrand
2021-03-25 11:23 ` Oscar Salvador
2021-03-25 12:35 ` Michal Hocko
2021-03-25 12:40 ` David Hildenbrand
2021-03-25 14:08 ` Michal Hocko
2021-03-25 14:09 ` David Hildenbrand
2021-03-25 14:34 ` Michal Hocko
2021-03-25 14:46 ` David Hildenbrand
2021-03-25 15:12 ` Michal Hocko
2021-03-25 15:19 ` David Hildenbrand [this message]
2021-03-25 15:35 ` Michal Hocko
2021-03-25 15:40 ` David Hildenbrand
2021-03-25 16:07 ` Michal Hocko
2021-03-25 16:20 ` David Hildenbrand
2021-03-25 16:36 ` Michal Hocko
2021-03-25 16:47 ` Michal Hocko
2021-03-25 16:55 ` David Hildenbrand
2021-03-25 22:06 ` Oscar Salvador
2021-03-26 8:35 ` Michal Hocko
2021-03-26 8:52 ` David Hildenbrand
2021-03-26 8:57 ` Oscar Salvador
2021-03-26 12:15 ` Oscar Salvador
2021-03-26 13:36 ` David Hildenbrand
2021-03-26 14:38 ` Michal Hocko
2021-03-26 14:53 ` David Hildenbrand
2021-03-26 15:31 ` Michal Hocko
2021-03-26 16:03 ` David Hildenbrand
2021-03-26 8:55 ` Oscar Salvador
2021-03-26 9:11 ` Michal Hocko
2021-03-25 18:08 ` David Hildenbrand
2021-03-25 12:26 ` Michal Hocko
2021-03-25 14:02 ` Oscar Salvador
2021-03-25 14:40 ` Michal Hocko
2021-03-19 9:26 ` [PATCH v5 2/5] acpi,memhotplug: Enable MHP_MEMMAP_ON_MEMORY when supported Oscar Salvador
2021-03-23 10:40 ` Michal Hocko
2021-03-19 9:26 ` [PATCH v5 3/5] mm,memory_hotplug: Add kernel boot option to enable memmap_on_memory Oscar Salvador
2021-03-23 10:47 ` Michal Hocko
2021-03-24 8:45 ` Oscar Salvador
2021-03-24 9:02 ` Michal Hocko
2021-03-19 9:26 ` [PATCH v5 4/5] x86/Kconfig: Introduce ARCH_MHP_MEMMAP_ON_MEMORY_ENABLE Oscar Salvador
2021-03-19 9:26 ` [PATCH v5 5/5] arm64/Kconfig: " Oscar Salvador
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