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    Subject[PATCH RESEND 1/2] ida: document IDA_BITMAP_LONGS calculation
    Date
    IDA_BITMAP_LONGS value is calculated take into account struct ida_bitmap
    not to waste memory space. Comment it.

    Signed-off-by: Namhyung Kim <namhyung@gmail.com>
    Acked-by: Tejun Heo <tj@kernel.org>
    ---
    include/linux/idr.h | 5 ++++-
    1 files changed, 4 insertions(+), 1 deletions(-)

    diff --git a/include/linux/idr.h b/include/linux/idr.h
    index e968db7..3f4b718 100644
    --- a/include/linux/idr.h
    +++ b/include/linux/idr.h
    @@ -117,10 +117,13 @@ void idr_init(struct idr *idp);
    /*
    * IDA - IDR based id allocator, use when translation from id to
    * pointer isn't necessary.
    + *
    + * IDA_BITMAP_LONGS is calculated to be one less to accommodate
    + * ida_bitmap->nr_busy so that the whole struct fits in 128 bytes.
    */
    #define IDA_CHUNK_SIZE 128 /* 128 bytes per chunk */
    #define IDA_BITMAP_LONGS (128 / sizeof(long) - 1)
    -#define IDA_BITMAP_BITS (IDA_BITMAP_LONGS * sizeof(long) * 8)
    +#define IDA_BITMAP_BITS (IDA_BITMAP_LONGS * sizeof(long) * 8)

    struct ida_bitmap {
    long nr_busy;
    --
    1.7.2.2


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