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    SubjectRe: [PATCH 15/18] fs: introduce a per-cpu last_ino allocator
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    Le vendredi 08 octobre 2010 à 06:03 -0400, Christoph Hellwig a écrit :
    > On Fri, Oct 08, 2010 at 10:56:58AM +0100, Al Viro wrote:
    > > FWIW, that one is begging to be split; what I mean is that there are
    > > two classes of callers; ones that will set i_ino themselves anyway
    > > and ones that really want i_ino invented. Two functions?
    >
    > There's no reason to add i_ino before adding it to the per-sb list,
    > we don't do so either for inodes acquired via iget. The fix is simply
    > to stop assigning i_ino in new_inode and call the helper to get it in
    > the place that need it after the call to new_inode. Later we can
    > even move to a lazy assignment scheme where needed. I'd also really
    > like to get a grip on why the simple counters if fine for some
    > filesystems while we need iunique() for others.

    If iunique() was scalable, sockets could use it, so that we can have
    hard guarantee two sockets on machine dont have same inum.

    A reasonable compromise here is to use a simple and scalable allocator,
    and take the risk two sockets have same inum.

    While it might break some applications playing fstats() games, on
    sockets, current schem is vastly faster.

    I worked with machines with millions of opened socket concurrently,
    iunique() was not an option, and application didnt care of possible inum
    clash.


    For disk files, inum _must_ be unique per fs, for sockets, its only if
    you want strict compliance to some standards.



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