From mboxrd@z Thu Jan  1 00:00:00 1970
From: David Miller <davem@davemloft.net>
Subject: Re: [rfc][patch] store-free path walking
Date: Thu, 08 Oct 2009 23:15:27 -0700 (PDT)
Message-ID: <20091008.231527.251721755.davem@davemloft.net>
References: <alpine.LFD.2.01.0910070742260.3432@localhost.localdomain>
	<20091008123622.GA30316@wotan.suse.de>
	<20091009035050.GC4287@wotan.suse.de>
Mime-Version: 1.0
Content-Type: Text/Plain; charset=us-ascii
Content-Transfer-Encoding: 7bit
Cc: torvalds@linux-foundation.org, jens.axboe@oracle.com,
	linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
	kiran@scalex86.org, peterz@infradead.org
To: npiggin@suse.de
Return-path: <linux-kernel-owner+glk-linux-kernel-3=40m.gmane.org-S932260AbZJIGPd@vger.kernel.org>
In-Reply-To: <20091009035050.GC4287@wotan.suse.de>
Sender: linux-kernel-owner@vger.kernel.org
List-Id: linux-fsdevel.vger.kernel.org

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.