linux-kernel - Re: [PATCH 0/4] dcache: make Oracle more scalable on large systems

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Message-ID: <20130222230048.GP26694@dastard>
Date:	Sat, 23 Feb 2013 10:00:48 +1100
From:	Dave Chinner <david@...morbit.com>
To:	Waiman Long <Waiman.Long@...com>
Cc:	Andi Kleen <andi@...stfloor.org>, linux-fsdevel@...r.kernel.org,
	Alexander Viro <viro@...iv.linux.org.uk>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/4] dcache: make Oracle more scalable on large systems

On Thu, Feb 21, 2013 at 11:13:27PM -0500, Waiman Long wrote:
> On 02/21/2013 07:13 PM, Andi Kleen wrote:
> >Dave Chinner<david@...morbit.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.

That seems to me like an application problem - poking at what the
kernel is doing via diagnostic interfaces so often that it gets in
the way of the kernel actually doing stuff is not a problem the
kernel can solve.

Cheers,

Dave.
-- 
Dave Chinner
david@...morbit.com
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