From: Theodore Ts'o <tytso@mit.edu>
Subject: Re: [PATCH 2/2] ext4: Reduce contention on s_orphan_lock
Date: Tue, 20 May 2014 09:57:23 -0400
Message-ID: <20140520135723.GB15177@thunk.org>
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Cc: Jan Kara <jack@suse.cz>, linux-ext4@vger.kernel.org
To: Thavatchai Makphaibulchoke <thavatchai.makpahibulchoke@hp.com>
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On Tue, May 20, 2014 at 02:33:23AM -0600, Thavatchai Makphaibulchoke wrote:
> Please see my one comment below.
> 
> BTW, I've run aim7 on your before I notice what I commented below.  There are workloads that my patch outperform yours and vice versa.  I will have to redo it over again.

Thavatchai, it would be really great if you could do lock_stat runs
with both Jan's latest patches as well as yours.  We need to
understand where the differences are coming from.

As I understand things, there are two differences between Jan and your
approaches.  The first is that Jan is using the implicit locking of
i_mutex to avoid needing to keep a hashed array of mutexes to
synchronize an individual inode's being added or removed to the orphan
list.

The second is that you've split the orphan mutex into an on-disk mutex
and a in-memory spinlock.

Is it possible to split up your patch so we can measure the benefits
of each of these two changes?  More interestingly, is there a way we
can use the your second change in concert with Jan's changes?

Regards,

						- Ted