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

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Date:	Thu, 08 Oct 2009 23:15:27 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	npiggin@...e.de
Cc:	torvalds@...ux-foundation.org, jens.axboe@...cle.com,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	kiran@...lex86.org, peterz@...radead.org
Subject: Re: [rfc][patch] store-free path walking

From: Nick Piggin <npiggin@...e.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.
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