Date: Wed, 25 Jan 2012 15:28:07 +1100 (EST) From: Bruce Evans <brde@optusnet.com.au> To: Rick Macklem <rmacklem@uoguelph.ca> Cc: svn-src-head@FreeBSD.org, Rick Macklem <rmacklem@FreeBSD.org>, svn-src-all@FreeBSD.org, src-committers@FreeBSD.org, Bruce Evans <brde@optusnet.com.au> Subject: Re: svn commit: r230516 - in head/sys: fs/nfsclient nfsclient Message-ID: <20120125152150.M1522@besplex.bde.org> In-Reply-To: <2145461054.81036.1327460551572.JavaMail.root@erie.cs.uoguelph.ca>
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On Tue, 24 Jan 2012, Rick Macklem wrote: > Bruce Evans wrote: >> On Wed, 25 Jan 2012, Rick Macklem wrote: >> >>> Log: >>> If a mount -u is done to either NFS client that switches it >>> from TCP to UDP and the rsize/wsize/readdirsize is greater >>> than NFS_MAXDGRAMDATA, it is possible for a thread doing an >>> I/O RPC to get stuck repeatedly doing retries. This happens >>> ... >> Could it wait for the old i/o to complete (and not start any new >> i/o?). This is little different from having to wait when changing >> from rw to ro. The latter is not easy, and at least the old nfs >> client seems to not even dream of it. ffs has always called a >> ... > As you said above "not easy ... uses complicated suspension of i/o". > I have not tried to code this, but I think it would be non-trivial. > The code would need to block new I/O before RPCs are issued and wait > for all in-progress I/Os to complete. At this time, the kernel RPC > handles the in-progress RPCs and NFS doesn't "know" what is > outstanding. Of course, code could be added to keep track of in-progress > I/O RPCs, but that would have to be written, as well. Hmm, this means that even when the i/o sizes are small, the mode switch from tcp to udp may be unsafe since there may still be i/o's with higher sizes outstanding. So to switch from tcp to udp, the user should first reduce the sizes, when wait a while before switching to udp. And what happens with retries after changing sizes up or down? Does it retry with the old sizes? Brucehome | help
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