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

From: Waiman Long
Date: Thu Feb 21 2013 - 23:13:34 EST

On 02/21/2013 07:13 PM, Andi Kleen wrote:
Dave Chinner<david@xxxxxxxxxxxxx> 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 ?


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.

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