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    SubjectRe: [bug] SLUB + mm/slab.c boot crash in -rc9

    * Christoph Lameter <> wrote:

    > > Pretty please, could you pay more than cursory attention to this bug
    > > i already spent two full days on and which is blocking the v2.6.25
    > > release?
    > Yeah trying to get to understand how exactly sparsemem works and how
    > the 32 bit highmem stuff interacts with it... Sorry not code that I am
    > an expert in nor the platform that I am familiar with. Code mods there
    > required heavy review from multiple parties with expertise in various
    > subjects.

    yeah - sorry about that impatient flame. And it could still be anything
    from the page allocator to bootmem - or some completely unrelated piece
    of code corrupting some key data structure.

    sparsemem is supposed to work roughly like this on x86 (32-bit):

    - the x86 memory map comes from the bios via e820.

    - those individual chunks of e820-enumerated memory get
    registered with mm/sparse.c's data structures via memory_present()
    callbacks. [btw., this should be renamed to register_memory_present()
    or register_sparse_range() - something less opaque.]

    - there's really just 3 RAM areas that matter on this box, and the last
    one is unusable for !PAE, which leaves 2.

    - there's a 256 MB PCI aperture hole at 0xf0000000.

    - out of the 64 sparse memory chunk the first 60 get filled in (all have
    at least partially some RAM content) - the last 4 [the PCI aperture
    hole] remains !present.

    - we pass in an array of 3 zones to free_area_init_nodes().

    - we free the lowmem pages into the buddy allocator via the usual
    generic setup

    - we have a special loop for highmem pages in arch/x86/mm/init_32.c,
    set_highmem_pages_init(). This just goes through the PFNs one by one
    and does an explicit __free_page() on all RAM pages that are in the
    mem_map[] and which are non-reserved.

    and that's it roughly.

    my current guess would have been some bootmem regression/interaction
    that messes up the buddy bitmaps - but i just reverted to the v2.6.24
    version of bootmem.c and that crashes too ...


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