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    SubjectRe: [PATCH] kernel parameter vmalloc size fix
    On Mon, Jun 16, 2008 at 4:01 PM, Ingo Molnar <mingo@elte.hu> wrote:
    >
    > * Dave Young <hidave.darkstar@gmail.com> wrote:
    >
    >> booting kernel with vmalloc=[any size<=16m] will oops.
    >>
    >> It's due to the vm area hole.
    >>
    >> In include/asm-x86/pgtable_32.h:
    >> #define VMALLOC_OFFSET (8 * 1024 * 1024)
    >> #define VMALLOC_START (((unsigned long)high_memory + 2 * VMALLOC_OFFSET - 1) \
    >> & ~(VMALLOC_OFFSET - 1))
    >>
    >> BUG_ON in arch/x86/mm/init_32.c will be triggered:
    >> BUG_ON((unsigned long)high_memory > VMALLOC_START);
    >>
    >> Fixed by return -EINVAL for invalid parameter
    >
    > hm. Why dont we instead add the size of the hole to the
    > __VMALLOC_RESERVE value instead? There's nothing inherently bad about
    > using vmalloc=16m. The VM area hole is really a kernel-internal
    > abstraction that should not be visible in the usage of the parameter.

    I do some test about this last weekend, there's some questions, could
    you help to fix it?

    1. MAXMEM :
    (-__PAGE_OFFSET - __VMALLOC_RESERVE).
    The space after VMALLOC_END is included as well, seting it to
    (VMALLOC_END - PAGE_OFFSET - __VMALLOC_RESERVE), is it right?

    2. VMALLOC_OFFSET is not considered in __VMALLOC_RESERVE
    Should fixed by adding VMALLOC_OFFSET to it.

    3. VMALLOC_START :
    (((unsigned long)high_memory + 2 * VMALLOC_OFFSET - 1) & ~(VMALLOC_OFFSET - 1))
    So it's not always 8M, bigger than 8M possible.
    Set it to ((unsigned long)high_memory + VMALLOC_OFFSET), is it right?

    Attached the proposed patch. please give some advice.

    Regards
    dave
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