On 27.07.2018 19:25, Pavel Tatashin wrote:
> Hi David,
>
> On Fri, Jul 27, 2018 at 12:55 PM David Hildenbrand <david@xxxxxxxxxx> wrote:
>>
>> Right now, struct pages are inititalized when memory is onlined, not
>> when it is added (since commit d0dc12e86b31 ("mm/memory_hotplug: optimize
>> memory hotplug")).
>>
>> remove_memory() will call arch_remove_memory(). Here, we usually access
>> the struct page to get the zone of the pages.
>>
>> So effectively, we access stale struct pages in case we remove memory that
>> was never onlined.
>
> Yeah, this is a bug, thank you for catching it.
>
>> So let's simply inititalize them earlier, when the
>> memory is added. We only have to take care of updating the zone once we
>> know it. We can use a dummy zone for that purpose.
>>
>> So effectively, all pages will already be initialized and set to
>> reserved after memory was added but before it was onlined (and even the
>> memblock is added). We only inititalize pages once, to not degrade
>> performance.
>
> Yes, but we still add one more npages loop, so there will be some
> performance degradation, but not severe.
>
> There are many conflicts with linux-next, please sync before sending
> out next patch.
Indeed, although I rebased, I was working on a branch based on Linus
tree ...
[...]
>> not_early:
>> page = pfn_to_page(pfn);
>> - __init_single_page(page, pfn, zone, nid);
>> - if (context == MEMMAP_HOTPLUG)
>> - SetPageReserved(page);
>> + if (context == MEMMAP_HOTPLUG) {
>> + /* everything but the zone was inititalized */
>> + set_page_zone(page, zone);
>> + set_page_virtual(page, zone);
>> + } else
>> + init_single_page(page, pfn, zone, nid);
>>
>
> Please add a new function:
> memmap_init_zone_hotplug() that will handle only the zone and virtual
> fields for onlined hotplug memory.
>
> Please remove: "enum memmap_context context" from everywhere.
All your comments make sense. Will look into the details next week and
send a new version.
Thanks and enjoy your weekend!
--
Thanks,
David / dhildenb
