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Extended attribute caching

To: linux-xfs@xxxxxxxxxxx
Subject: Extended attribute caching
From: Ravi Wijayaratne <ravi_wija@xxxxxxxxx>
Date: Wed, 29 Oct 2003 11:09:29 -0800 (PST)
Cc: lord@xxxxxxx, sandeen@xxxxxxx
Sender: linux-xfs-bounce@xxxxxxxxxxx

I wanted to find out what performance impact setting/getting extended
attributes would have on file I/O on XFS. Therefore for every file I/O
I set a 4 byte extended attribute in "user" name space. The performance
dropped approximately 30%. 

I have the following questions regarding this observation.

1. Are extended attributes cached ? If so I should see a performance
impact of perhaps doing stat which accesses the cached inode structures
if present. Substituting a stat call instead of setxattr call, only had
approximately 6% drop in performance. Why is the discrepency ?

2. I know that inodes are cached. Are user name space EAs stored inside the 
inode ?
If not, is there a user space utility or another name space, "system" or "root"
that I could use to force EAs to be stored inside the inode so that I can be 
that it will be cached ?

3. Could setting extensive amounts of extended attributes disrupt the 
operations in the log and hence cause adverse effects ? 

Thank you


Ravi Wijayaratne

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