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

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