linux-kernel - Re: is nfsd sync or async?

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Message-ID: <AANLkTimaOiC4eo3Zqn-wO62sV9hVMsNeF-vqkMGi6kVR@mail.gmail.com>
Date:	Mon, 9 Aug 2010 22:44:35 -0400
From:	Yuehai Xu <yuehaixu@...il.com>
To:	linux-nfs@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, green.trace@...il.com,
	yuehai.xu@...il.com, yhxu@...ne.edu
Subject: Re: is nfsd sync or async?

On Mon, Aug 9, 2010 at 8:00 AM, Yuehai Xu <yuehaixu@...il.com> wrote:
> Hi all,
>
> Suppose there is only one nfsd and two clients are sending random read
> requests to this daemon. In this way, read ahead of the client should
> not work since the requests are random. The requests between these two
> clients should be async, while the requests from any one client of the
> two should be sync. My question is about how will the nfsd handle
> these requests, using sync or async mode in the kernel? Say, will nfsd
> never handle the next request unless the previous request has been
> served, without considering which clients the request belongs to? Or
> nfsd just dispatch async requests to the lower level as soon as it
> receives a request?
>
> Any answer will be appreciate!
>
> Yuehai
>

I review the code of NFS and notice that the read operation of NFS
will invoke generic_file_aio_read(), which means the requests(from the
case I mentioned above) dispatched by a nfsd should be sync to each
other, is that correct?

Thanks,
Yuehai
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