From mboxrd@z Thu Jan  1 00:00:00 1970
From: Al Viro <viro@ZenIV.linux.org.uk>
Subject: Re: [LSF/MM TOPIC] Parallelize file operation (like creation,
 unlink) under large shared directory
Date: Sun, 22 Jan 2012 20:39:36 +0000
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On Sun, Jan 22, 2012 at 12:31:31PM -0800, wangdi wrote:

> We actually already implemented this for ext4, and we saw a lot performance improvement(at least 30% improvements for open/create in a single directory)for lustre stack,
> but we want to make this improvement accessible through the VFS. Probably XFS and Btrfs could also benefit from this.

You do realize that i_mutex locking is relied upon for protection of a lot
of stuff besides the obvious (i.e. on-disk directory contents)?

I'm not saying that it's hopeless, but it's highly non-trivial; the things
like rmdir/mount races, access to ->d_parent/->d_name in a lot of code,
etc. need to be taken care of and it is a _lot_ of code review to deal
with - just to verify the correctness of such changes.