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    SubjectRe: Question on the VFS inode structure.

    On Wed, 27 Oct 1999, Malcolm Beattie wrote:

    > I don't remember exactly what you proposed for this, but if you are
    > intending to replace the inode structure with a generic one which has
    > a pointer to a separately allocated per-fs structure then here's a
    > warning. Digital UNIX used to that but had to change it exactly the
    > opposite way for performance reasons. Its vnode structure used to
    > have a v_data pointer to a separately allocated per-fs "private"
    > structure. However, performance was bad because of the pointer
    > following and the extra fragmentation. They ended up reuniting the two

    Ouch. From what I've seen in Vahalia they seem to be doing ungodly amount
    of directory accesses - even worse than 4.4BSD. Completely different load
    _and_ mix. So I seriously doubt that we can apply their data.

    > so that they could allocate the whole (generic + private) structure in
    > one chunk and then made v_data point to directly after the generic
    > part (i.e. the start of the no-longer-separate private part).
    > They did the same with their ungodly mixture of BSD and Mach
    > structures for tasks and threads: they had separate struct task,
    > struct proc and struct utask which they combined into a single struct
    > super_task (though still with pointers between the supposedly
    > "separate" bits) and they had separate struct thread and struct
    > np_uthread which they combined into struct super_thread.


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