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    SubjectRe: [PATCH] mm: Fix memory hotplug oops from ZONE_MOVABLE changes.
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    On (20/07/07 15:03), Paul Mundt didst pronounce:
    > zone_movable_pfn is presently marked as __initdata and referenced
    > from adjust_zone_range_for_zone_movable(), which in turn is
    > referenced by zone_spanned_pages_in_node(). Both of these are
    > __meminit annotated. When memory hotplug is enabled, this will oops
    > on a hot-add, due to zone_movable_pfn having been freed.
    >

    Ouch. Thanks for catching, your patch looks good. Before I add the ack though,
    I would like to get more details of the error in case there are other gremlins
    I haven't thought of and the fix for memory-hotadd is more complex.

    First, can you confirm this is node hot-add please? I'm haven't looked at
    the memory hot-add code in a while so I would like to be sure this problem
    path only exists on node hot-add. If it is node hot-add, then everything
    should be ok. The memory should get added to the same zone as it did in
    older kernels.

    Even if this is node hot-add, can you confirm that "ordinary" memory hot-add
    is working as expected when ZONE_MOVABLE exists please? To test, add a boot
    parameter kernelcore=N where N == 80% of memory and hot-add some memory to
    an existing node.

    I expect that the memory gets added to the same zone as historically but
    when ZONE_MOVABLE is set, you'll see a situation where zones are overlapping
    after memory hot-add. i.e. Before memory hot-add, you'd see

    DDDDMM

    for ZONE_DMA and ZONE_MOVABLE and after hotadd, you'd see something like

    DDDDMMDDDD

    so /proc/zoneinfo will look unusual. I'd like to be sure the memory exists
    where you expect it to exist and that there are no problems after hot-add. To
    test, a simple memory hot-add followed by a dd of a file the size of all
    physical memory followed by a delete should do the trick. Also make sure
    files like /proc/zoneinfo and /proc/meminfo are ok and particularly that
    sysrq+m produces sensible output.

    The only in-kernel user that should notice is one that is trying to walk the
    whole of memmap and is using page_zone() changing to detect boundaries. The
    existing users I am aware of only walk within a MAX_ORDER_NR_PAGES boundary
    usually and a memory section boundary at most. Those users will be ok even
    if zones overlap.

    Thanks a lot.

    If other memory-hotadd users are watching, I'd appreciate a test and a report
    with a recent -git kernel to confirm you're ok. Is there a way currently
    of simulating memory-hotadd so I can try this out? Ages ago, one could boot
    with mem= and "add" the remaining memory at run-time.

    > __meminitdata annotation gives the desired behaviour.
    >
    > This will only impact platforms that enable both memory hotplug
    > and ARCH_POPULATES_NODE_MAP.
    >
    > Signed-off-by: Paul Mundt <lethal@linux-sh.org>
    >
    > --
    >
    > mm/page_alloc.c | 2 +-
    > 1 file changed, 1 insertion(+), 1 deletion(-)
    >
    > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
    > index 43cb3b3..40954fb 100644
    > --- a/mm/page_alloc.c
    > +++ b/mm/page_alloc.c
    > @@ -138,7 +138,7 @@ static unsigned long __meminitdata dma_reserve;
    > #endif /* CONFIG_MEMORY_HOTPLUG_RESERVE */
    > unsigned long __initdata required_kernelcore;
    > unsigned long __initdata required_movablecore;
    > - unsigned long __initdata zone_movable_pfn[MAX_NUMNODES];
    > + unsigned long __meminitdata zone_movable_pfn[MAX_NUMNODES];
    >
    > /* movable_zone is the "real" zone pages in ZONE_MOVABLE are taken from */
    > int movable_zone;

    --
    --
    Mel Gorman
    Part-time Phd Student Linux Technology Center
    University of Limerick IBM Dublin Software Lab
    -
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