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

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Message-ID: <b572b20f-b7fb-2558-5c79-d0beb65d7f2e@redhat.com>
Date:   Wed, 30 Oct 2019 09:14:23 +0100
From:   David Hildenbrand <david@...hat.com>
To:     linux-kernel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-mm@...ck.org, Michal Hocko <mhocko@...e.com>,
        Oscar Salvador <osalvador@...e.de>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        Dan Williams <dan.j.williams@...el.com>,
        Pavel Tatashin <pasha.tatashin@...een.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [PATCH v1] mm/memory_hotplug: Fix updating the node span

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