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Date: Thu, 21 Feb 2013 23:13:27 -0500
From: Waiman Long <Waiman.Long@hp.com>
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To: Andi Kleen <andi@firstfloor.org>
CC: Dave Chinner <david@fromorbit.com>, linux-fsdevel@vger.kernel.org,
        Alexander Viro <viro@zeniv.linux.org.uk>, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 0/4] dcache: make Oracle more scalable on large systems
References: <1361299859-27056-1-git-send-email-Waiman.Long@hp.com> <20130221233818.GM26694@dastard> <m2bobdxl1i.fsf@firstfloor.org>
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On 02/21/2013 07:13 PM, Andi Kleen wrote:
> Dave Chinner<david@fromorbit.com>  writes:
>
>> On Tue, Feb 19, 2013 at 01:50:55PM -0500, Waiman Long wrote:
>>> It was found that the Oracle database software issues a lot of call
>>> to the seq_path() kernel function which translates a (dentry, mnt)
>>> pair to an absolute path. The seq_path() function will eventually
>>> take the following two locks:
>> Nobody should be doing reverse dentry-to-name lookups in a quantity
>> sufficient for it to become a performance limiting factor. What is
>> the Oracle DB actually using this path for?
> Yes calling d_path frequently is usually a bug elsewhere.
> Is that through /proc ?
>
> -Andi
>
>
A sample strace of Oracle indicates that it opens a lot of /proc 
filesystem files such as the stat, maps, etc many times while running. 
Oracle has a very detailed system performance reporting infrastructure 
in place to report almost all aspect of system performance through its 
AWR reporting tool or the browser-base enterprise manager. Maybe that is 
the reason why it is hitting this performance bottleneck.

Regards,
Longman