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    SubjectRe: Size of 2.6.20 task_struct on x86_64 machines
    On Thu, 08 Feb 2007 12:19:45 -0800 (PST)
    David Miller <davem@davemloft.net> wrote:

    > From: William Cohen <wcohen@redhat.com>
    > Date: Thu, 08 Feb 2007 11:14:13 -0500
    >
    > > This past week I was playing around with that pahole tool
    > > (http://oops.ghostprotocols.net:81/acme/dwarves/) and looking at the
    > > size of various struct in the kernel. I was surprised by the size of
    > > the task_struct on x86_64, approaching 4K. I looked through the
    > > fields in task_struct and found that a number of them were declared as
    > > "unsigned long" rather than "unsigned int" despite them appearing okay
    > > as 32-bit sized fields. On x86_64 "unsigned long" ends up being 8
    > > bytes in size and forces 8 byte alignment. Is there a reason there
    > > a reason they are "unsigned long"?
    >
    > I think at one point we used the atomic bit operations to operate on
    > things like tsk->flags, and those interfaces require unsigned long as
    > the type.
    >
    > That doesn't appear to be the case any longer, so at a minimum
    > your tsk->flags conversion to unsigned int should be ok.

    Yeah, afacit everything in there is OK and happily all the
    converted-to-32-bit quantities happen to be contiguous with other 32-bit
    quantities.

    Most architectures' bitops functions take unsigned long * so if anyone is
    using bitops on these things we should get to hear about it.

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