Re: [PATCH v2 1/3] mm/shuffle: don't move pages between zones and don't read garbage memmaps

["Williams, Dan J" <dan.j.williams@intel.com>]

On Fri, 2020-06-19 at 14:59 +0200, David Hildenbrand wrote:
> Especially with memory hotplug, we can have offline sections (with a
> garbage memmap) and overlapping zones. We have to make sure to only
> touch initialized memmaps (online sections managed by the buddy) and
> that
> the zone matches, to not move pages between zones.
> 
> To test if this can actually happen, I added a simple
> 	BUG_ON(page_zone(page_i) != page_zone(page_j));
> right before the swap. When hotplugging a 256M DIMM to a 4G x86-64 VM
> and
> onlining the first memory block "online_movable" and the second
> memory
> block "online_kernel", it will trigger the BUG, as both zones (NORMAL
> and MOVABLE) overlap.
> 
> This might result in all kinds of weird situations (e.g., double
> allocations, list corruptions, unmovable allocations ending up in the
> movable zone).
> 
> Fixes: e900a918b098 ("mm: shuffle initial free memory to improve
> memory-side-cache utilization")
> Acked-by: Michal Hocko <mhocko@suse.com>
> Cc: stable@vger.kernel.org # v5.2+
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Johannes Weiner <hannes@cmpxchg.org>
> Cc: Michal Hocko <mhocko@suse.com>
> Cc: Minchan Kim <minchan@kernel.org>
> Cc: Huang Ying <ying.huang@intel.com>
> Cc: Wei Yang <richard.weiyang@gmail.com>
> Cc: Mel Gorman <mgorman@techsingularity.net>
> Signed-off-by: David Hildenbrand <david@redhat.com>

Looks good to me.

Acked-by: Dan Williams <dan.j.williams@intel.com>