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    SubjectRe: [rfc][patch] store-free path walking
    On Thu, Oct 08, 2009 at 11:15:27PM -0700, David Miller wrote:
    > From: Nick Piggin <npiggin@suse.de>
    > Date: Fri, 9 Oct 2009 05:50:50 +0200
    >
    > > OK, I got rid of this guy from the RCU walk. Basically now hold
    > > vfsmount_lock over the entire RCU path walk (which also pins the mnt)
    > > and use a seqlock in the fs struct to get a consistent mnt,dentry
    > > pair. This also simplifies the walk because we don't need the
    > > complexity to avoid mntget/mntput (just do one final mntget on the
    > > resulting mnt before dropping vfsmount_lock).
    > >
    > > vfsmount_lock adds one per-cpu atomic for the spinlock, and we
    > > remove two thread-shared atomics for fs->lock so a net win for
    > > both single threaded performance and thread-shared scalability.
    > > Latency is no problem because we hold rcu_read_lock for the same
    > > length of time anyway.
    > >
    > > The parallel git diff workload is improved by serveral percent.
    >
    > Sounds sweet Nick, can't wait to play with your next set of
    > patches here.

    http://www.kernel.org/pub/linux/kernel/people/npiggin/patches/fs-scale/

    OK well there will be another rev of the patches there with everything,
    also with the d_mounted patch so dentry remains a nice size. Also tried
    rearranging some structures in the dentry to help lookups but haven't
    quite finished there.

    Jens I would be interested to see whether parallel case on the N2 is
    improved at all. Profiles from that case might be interesting.



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