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    SubjectRe: [PATCH 07/17] fs: icache atomic inodes_stat
    On Wed, Sep 29, 2010 at 09:52:53PM -0700, Andrew Morton wrote:
    > On Wed, 29 Sep 2010 22:18:39 +1000 Dave Chinner <david@fromorbit.com> wrote:
    > > From: Nick Piggin <npiggin@suse.de>
    > >
    > > The inode use statistics are currently protected by the inode_lock.
    > > Before we can remove the inode_lock, we need to protect these
    > > counters against races. Do this by converting them to atomic
    > > counters so they ar enot dependent on any lock at all.
    >
    > typo

    It's Dave, I swear :)


    > > +struct inodes_stat_t {
    > > + atomic_t nr_inodes;
    > > + atomic_t nr_unused;
    > > + int dummy[5]; /* padding for sysctl ABI compatibility */
    > > +};
    >
    > OK, that's a hack. The first two "ints" are copied out to userspace.
    > This change assumes that sizeof(atomic_t)=4 and that an atomic_t has
    > the same layout, alignment and padding as an int.
    >
    > Probably that's true in current kernels and with current architectures
    > but it's a hack and it's presumptive.
    >
    > It shouldn't be snuck into the tree unchangelogged and uncommented.
    >
    > (time passes)
    >
    > OK, I see that all of this gets reverted later on. Please update the
    > changelog so the next reviewer doesn't get fooled.

    Yeah it is. I might end up folding the per-cpu stuff back over it
    and avoid the issue completely. Otherwise I'll add a comment.



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