Re: [rfc][patch] store-free path walking

[Nick Piggin]

On Thu, Oct 08, 2009 at 11:15:27PM -0700, David Miller wrote:
> From: Nick Piggin <npiggin@xxxxxxx>
> 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.

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/