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Re: concurrent direct IO write in xfs

To: Dave Chinner <david@xxxxxxxxxxxxx>
Subject: Re: concurrent direct IO write in xfs
From: Zheng Da <zhengda1936@xxxxxxxxx>
Date: Mon, 23 Jan 2012 15:51:43 -0500
Cc: xfs@xxxxxxxxxxx
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On Mon, Jan 23, 2012 at 2:34 PM, Zheng Da <zhengda1936@xxxxxxxxx> wrote:
> I build XFS on the top of ramdisk. So yes, there is a lot of small
> concurrent writes in a second.
> I create a file of 4GB in XFS (the ramdisk has 5GB of space). My test
> program overwrites 4G of data to the file and each time writes a page of
> data randomly to the file. It's always overwriting, and no appending. The
> offset of each write is always aligned to the page size. There is no
> overlapping between writes.

Why are you using XFS for this? tmpfs was designed to do this sort
of stuff as efficiently as possible....
OK, I can try that. 
tmpfs doesn't support direct IO. 

> So the test case is pretty simple and I think it's easy to reproduce it.
> It'll be great if you can try the test case.

Can you post your test code so I know what I test is exactly what
you are running?
I can do that. My test code gets very complicated now. I need to simplify it.
Here is the code. It's still a bit long. I hope it's OK.
You can run the code like "rand-read file option=direct pages=1048576 threads=8 access=write/read".


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