On 2/15/12 3:32 PM, Marc Aurele La France wrote:
On Wed, 15 Feb 2012, Tom Tucker wrote:
This looks correct to me.
... except that it doesn't work, and neither does your change at
http://git.openfabrics.org/git?p=~boomer/ofed_kernel/.git;a=commitdiff;h=217d68a9e4f8cb9c735e1098646f41fb36744ce9
I assume these are v3 mounts?
Yes.
Ok, "good", because I have a patch that I had to make a change to get v4
to work.
BTW, the when you say you're running NFS/TCP are you running TCP over
IPoIB?
I have experienced issues with takeover/giveback between
Also yes.
/
In any case, I've switched back to NFS/TCP/IPoIB with a 2044 MTU (had
to reboot everything to get that done). So NFS/RDMA remains highly
experimental in my eyes. And it will remain so until the Linux kernel
community and the OpenFabrics community get their co-operation issues
resolved, if ever.
Marc.
On 1/12/12 1:17 PM, Marc Aurele La France wrote:
Greetings.
I am currently in the process of moving a cluster I administer from
NFS/TCP to NFS/RDMA, and am running into a number of issues I'd like
some
assistance with. Googling these doesn't help.
For background on what caused me to move to NFS/TCP in the first place,
please see the thread that starts at http://lkml.org/lkml/2010/8/23/204
The main reason I'm moving away from NFS/TCP is that something
happened in
the later kernels that reduces its resilience. Specifically, the
client
now permanently loses contact with the server whenever the latter
fails to
allocate an RPC sk_buff due to memory fragmentation. Restarting the
server's nfsd's fixes this problem, at least temporarily.
I have seen this behavior 'forever'. Perhaps you weren't getting the
memory exhaustion on the older kernels?
I haven't nailed down when this started happening (somewhere since
2.6.38), nor am I inclined to do so. This new experience (for me) with
NFS/TCP has conclusively shown me that it is much more responsive with
smaller IPoIB MTU's. Thus I will instead be reducing that MTU from its
connected mode maximum of 65520, perhaps all the way down to datagram
mode's 2044, to completely factor out memory fragmentation effects.
More
on that below.
Perhaps you are really comparing UD to CM?
In moving to NFS/RDMA and reducing the IPoIB MTU, I have seen the
following behaviours.
--
1) Random client-side BUG()'outs. In fact, these never finish
producing a
complete stack trace. I've tracked this down to duplicate replies
being
encountered by rpcrdma_reply_handler() in
net/sunrpc/xprtrdma/rpc_rdma.c.
Frankly I don't see why rpcrdma_reply_handler() should BUG() out in
that
case given TCP's behaviour in similar situations, documented
requirements
for the use of BUG() & friends in the first place, and the fact that
rpcrdma_reply_handler() essentially "ignores" replies for which it
cannot
find a corresponding request.
For the past few days now, I've been running the following on some
of my
nodes with no ill effects. And yes, I do see the log message this
produces. This changes rpcrdma_reply_handler() to treat duplicate
replies
in much the same way it treats replies for which it cannot find a
request.
diff -adNpru linux-3.1.6/net/sunrpc/xprtrdma/rpc_rdma.c
devel-3.1.6/net/sunrpc/xprtrdma/rpc_rdma.c
--- linux-3.1.6/net/sunrpc/xprtrdma/rpc_rdma.c 2011-12-21
14:00:46.000000000 -0700
+++ devel-3.1.6/net/sunrpc/xprtrdma/rpc_rdma.c 2011-12-29
07:25:59.000000000 -0700
@@ -776,7 +776,13 @@ repost:
" RPC request 0x%p xid 0x%08x\n",
__func__, rep, req, rqst, headerp->rm_xid);
- BUG_ON(!req || req->rl_reply);
+ /* req cannot be NULL here */
+ if (req->rl_reply) {
+ spin_unlock(&xprt->transport_lock);
+ printk(KERN_NOTICE "RPC: %s: duplicate replies to request
0x%p: "
+ "0x%p and 0x%p\n", __func__, req, req->rl_reply, rep);
+ goto repost;
+ }
/* from here on, the reply is no longer an orphan */
req->rl_reply = rep;
This would also apply, modulo patch fuzz, all the way back to 2.6.24.
--
2) Still client-side, I'm seeing a lot of these sequences ...
rpcrdma: connection to 10.0.6.1:20049 on mthca0, memreg 6 slots 32
ird 4
rpcrdma: connection to 10.0.6.1:20049 closed (-103)
103 is ECONNABORTED. memreg 6 is RPCRDMA_ALLPHYSICAL, so I'm
assuming my
Mellanox adapters don't support the default RPCRDMA_FRMR (memreg
5). I've
traced these aborted connections to IB_CM_DREP_RECEIVED events being
received by cma_ib_handler() in drivers/infiniband/core/cma.c, but
can go
no further given my limited understanding of what this code is
supposed to
do. I am guessing though, that these would presumably disappear when
switching back to datagram mode (cm == connected mode). These messages
don't appear to affect anything (the client simply reconnects and I've
seen no data corruption), but it would still be nice to know what's
going
on here.
You could try turning on debug as such "echo 511 >
/proc/sys/sunrpc/rpc_debug" and you will get lots of additional
information. Note, however, that those messages above are "normal". The
first one will occur when the mount happens, and the second when the
connection is closed; which occurs after 5-6 minutes of inactivity on
the mount.
--
3) isn't related to NFS/RDMA per se, but to my attempts at reducing the
IPoIB MTU. Whenever I do so on the fly across the cluster, some but
not
all, IPoIB traffic simply times out. Even, in some cases, TCP
connections
accept()'ed after the MTU reduction. Oddly, neither NFS/TCP nor
NFS/RDMA
seem affected, but other things (MPI apps, torque, etc.) are, whether
started before or after the change. So, something, somewhere,
remembers
the previous (larger) MTU (opensm?). It seems that the only way to
clear
this "memory" is to reboot the entire cluster, something I'd rather
avoid
if possible.
NFSRDMA doesn't run over IPoIB, so it doesn't care what you've set the
IPoIB MTU to be.
--
4) Lastly, I would like to ask for a better understanding of the
relationship, if any, between NFS/RDMA and the IPoIB MTU, and between
NFS/RDMA and [rw]size NFS mount parameters. What effect do these
have on
NFS/RDMA? For [rw]size, I have found that specifying less than a
page (4K) results in data corruption.
None.
--
Please CC me on any comments/flames about any of the above as I am not
subscribed to this list.
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