On 06.10.19 10:56, David Hildenbrand wrote:
Let's limit shrinking to !ZONE_DEVICE so we can fix the current code. We
should never try to touch the memmap of offline sections where we could
have uninitialized memmaps and could trigger BUGs when calling
page_to_nid() on poisoned pages.
There is no reliable way to distinguish an uninitialized memmap from an
initialized memmap that belongs to ZONE_DEVICE, as we don't have
anything like SECTION_IS_ONLINE we can use similar to
pfn_to_online_section() for !ZONE_DEVICE memory. E.g.,
set_zone_contiguous() similarly relies on pfn_to_online_section() and
will therefore never set a ZONE_DEVICE zone consecutive. Stopping to
shrink the ZONE_DEVICE therefore results in no observable changes,
besides /proc/zoneinfo indicating different boundaries - something we
can totally live with.
Before commit d0dc12e86b31 ("mm/memory_hotplug: optimize memory
hotplug"), the memmap was initialized with 0 and the node with the
right value. So the zone might be wrong but not garbage. After that
commit, both the zone and the node will be garbage when touching
uninitialized memmaps.
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Oscar Salvador <osalvador@xxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: Pavel Tatashin <pasha.tatashin@xxxxxxxxxx>
Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
Fixes: d0dc12e86b31 ("mm/memory_hotplug: optimize memory hotplug")
@Andrew, can you convert that toFixes: f1dd2cd13c4b ("mm, memory_hotplug: do not associate hotadded memory to zones until online") # visible after d0dc12e86b319
and add Cc: stable@xxxxxxxxxxxxxxx # v4.13+ -- Thanks, David / dhildenb
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