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    SubjectRe: [RFC] SLUB - define OO_ macro instead of hardcoded numbers
    On Wed, 22 Oct 2008, Cyrill Gorcunov wrote:

    > [Christoph Lameter - Wed, Oct 22, 2008 at 11:10:56AM -0700]
    >> On Wed, 22 Oct 2008, Cyrill Gorcunov wrote:
    >>
    >>> +#define OO_SHIFT 16
    >>> +#define OO_MASK ((1 << OO_SHIFT) - 1)
    >>> +#define MAX_OBJS_PER_PAGE 65535 /* see struct page.objects */
    >>
    >> This is == OO_MASK right? Otherwise things will break when we change
    >> OO_SHIFT.
    >>
    >
    > Yes, I set it 65535 directly to distinguish it from OO_MASK
    > meaning not value and point to page.objects since they are
    > u16. Which meant that is the point where all limits start.
    > So it we set OO_SHIFT to say 14 it will not be a problem
    > but if we exceed 16 bits it will break SLUB. Am I right?
    > (I become scratching the head :)

    If you set it > 16 then the size of the field in struct page is violated.

    So

    #define MAX_OBJ_PER_PAGE MIN(1 << bits_in(page.objects) - 1, OO_MASK)

    ?




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