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    SubjectRe: [RFC] SLUB - define OO_ macro instead of hardcoded numbers
    [Pekka Enberg - Wed, Oct 22, 2008 at 08:50:56PM +0300]
    > Christoph Lameter wrote:
    >> On Wed, 22 Oct 2008, Cyrill Gorcunov wrote:
    >>
    >>> Christoph how about this one?
    >>
    >> Ok. Looks a bit better but we still have two maxes here
    >>
    >> s->max which refers to the maximum number of objects per slab page for
    >> a specific slab cache (depends on the runtime configuration).
    >> OO_MAX_OBJS refers to the maximum number of objects per slab page that
    >> any slab cache can be configured for which is a compile time limit.
    >>
    >> Maybe this is okay, Pekka?
    >
    > Maybe call the page->objects maximum MAX_OBJS_PER_PAGE as it's not
    > strictly related to the other OO code?
    >
    > Pekka
    >

    Something like that?

    - Cyrill -
    ---

    mm/slub.c | 18 +++++++++++-------
    1 file changed, 11 insertions(+), 7 deletions(-)

    Index: linux-2.6.git/mm/slub.c
    ===================================================================
    --- linux-2.6.git.orig/mm/slub.c 2008-10-22 21:11:26.000000000 +0400
    +++ linux-2.6.git/mm/slub.c 2008-10-22 21:57:11.000000000 +0400
    @@ -153,6 +153,10 @@
    #define ARCH_SLAB_MINALIGN __alignof__(unsigned long long)
    #endif

    +#define OO_SHIFT 16
    +#define OO_MASK ((1 << OO_SHIFT) - 1)
    +#define MAX_OBJS_PER_PAGE 65535 /* see struct page.objects */
    +
    /* Internal SLUB flags */
    #define __OBJECT_POISON 0x80000000 /* Poison object */
    #define __SYSFS_ADD_DEFERRED 0x40000000 /* Not yet visible via sysfs */
    @@ -290,7 +294,7 @@ static inline struct kmem_cache_order_ob
    unsigned long size)
    {
    struct kmem_cache_order_objects x = {
    - (order << 16) + (PAGE_SIZE << order) / size
    + (order << OO_SHIFT) + (PAGE_SIZE << order) / size
    };

    return x;
    @@ -298,12 +302,12 @@ static inline struct kmem_cache_order_ob

    static inline int oo_order(struct kmem_cache_order_objects x)
    {
    - return x.x >> 16;
    + return x.x >> OO_SHIFT;
    }

    static inline int oo_objects(struct kmem_cache_order_objects x)
    {
    - return x.x & ((1 << 16) - 1);
    + return x.x & OO_MASK;
    }

    #ifdef CONFIG_SLUB_DEBUG
    @@ -764,8 +768,8 @@ static int on_freelist(struct kmem_cache
    }

    max_objects = (PAGE_SIZE << compound_order(page)) / s->size;
    - if (max_objects > 65535)
    - max_objects = 65535;
    + if (max_objects > MAX_OBJS_PER_PAGE)
    + max_objects = MAX_OBJS_PER_PAGE;

    if (page->objects != max_objects) {
    slab_err(s, page, "Wrong number of objects. Found %d but "
    @@ -1819,8 +1823,8 @@ static inline int slab_order(int size, i
    int rem;
    int min_order = slub_min_order;

    - if ((PAGE_SIZE << min_order) / size > 65535)
    - return get_order(size * 65535) - 1;
    + if ((PAGE_SIZE << min_order) / size > MAX_OBJS_PER_PAGE)
    + return get_order(size * MAX_OBJS_PER_PAGE) - 1;

    for (order = max(min_order,
    fls(min_objects * size - 1) - PAGE_SHIFT);

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