Re: [PATCH v1] mm/memory_hotplug: Fix updating the node span

[David Hildenbrand]

On 27.10.19 23:27, David Hildenbrand wrote:
> We recently started updating the node span based on the zone span to
> avoid touching uninitialized memmaps.
>
> Currently, we will always detect the node span to start at 0, meaning a
> node can easily span too many pages. pgdat_is_empty() will still work
> correctly if all zones span no pages. We should skip over all zones without
> spanned pages and properly handle the first detected zone that spans pages.
>
> Unfortunately, in contrast to the zone span (/proc/zoneinfo), the node span
> cannot easily be inspected and tested. The node span gives no real
> guarantees when an architecture supports memory hotplug, meaning it can
> easily contain holes or span pages of different nodes.
>
> The node span is not really used after init on architectures that support
> memory hotplug. E.g., we use it in mm/memory_hotplug.c:try_offline_node()
> and in mm/kmemleak.c:kmemleak_scan(). These users seem to be fine.
>
> Fixes: 00d6c019b5bc ("mm/memory_hotplug: don't access uninitialized memmaps in shrink_pgdat_span()")


@Andrew, can we also give this a churn, we should try to get this into 
5.4 due to

$ git tag --contains 00d6c019b5bc
[...]
v5.4-rc5

Thanks!

--

Thanks,

David / dhildenb