Re: size of nfsv4 writes

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



On Jun 12, 2008, at 5:41 PM, Olga Kornievskaia wrote:
Olga Kornievskaia wrote:
Trond Myklebust wrote:
On Wed, 2008-06-04 at 12:40 -0400, Olga Kornievskaia wrote:
While testing NFSv4 performance over the 10GE network, we are seeing the following behavior and would like to know if it is normal or a bug in the client code.

The server offers the max_write of 1M. The client mounts the server with the "wsize" option of 1M. Yet during the write we are seeing that the write size is at most 49K. Why does client never come close to 1M limit?

I have a feeling that is due to some crap in the VM. I'm currently
investigating a situation where it appears we're sending 1 COMMIT for
every 1-5 32k WRITEs. This is not a policy that stems from the NFS
client, so it would appear that the VM is being silly about things.

I'm specially suspicious of the code in get_dirty_limits() that is
setting a limit to the number of dirty pages based on the number of
pages a given BDI has written out in the recent past. As far as I can see, the intention is to penalise devices that are slow writers, but in
practice it doesn't do that: it penalises the devices that have the
least activity.

I think we are seeing larger than usual number of COMMIT messages.
Using Chuck's nfs-iostats to monitor an NFS write I can see that each operation writes about 830MB. Why is so much small than wsize=1M?


I assume you mean 830KB.

Remember that nfs-iostats reports an average transfer size, so you may be seeing a lot of 1MB writes on the wire, and just enough small writes to reduce the average. Or, the client may not be writing 1MB at all.

You have to look at a network trace to see which.

On the other hand, 830KB is still very large.

--
Chuck Lever
chuck[dot]lever[at]oracle[dot]com
--
To unsubscribe from this list: send the line "unsubscribe linux-nfs" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html

[Index of Archives]     [Linux Filesystem Development]     [Linux USB Development]     [Linux Media Development]     [Video for Linux]     [Linux NILFS]     [Linux Audio Users]     [Yosemite Info]     [Linux SCSI]

  Powered by Linux