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    SubjectRe: [RFC] SLUB - define OO_ macro instead of hardcoded numbers
    [Christoph Lameter - Wed, Oct 22, 2008 at 11:24:58AM -0700]
    > 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)
    >
    > ?
    >
    >

    Looks really good for me (if it worth anything). But Christoph
    doesn't OO_SHIT inspired by u16 too which means we could use
    MAX_OBJ_PER_PAGE in form you mentoined but maybe we should define

    #define OO_SHIFT bits_in(page.objects) to point out why we use
    16 not 14, not 18 or whatever? How do you think?

    - Cyrill -


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