Re: [PATCH RFC v5 0/2] nfsd: Initial implementation of NFSv4 Courteous Server

[dai.ngo@oracle.com]

On 11/29/21 11:03 AM, Chuck Lever III wrote:
> Hello Dai!
>
>
>> On Nov 29, 2021, at 1:32 PM, Dai Ngo <dai.ngo@oracle.com> wrote:
>>
>>
>> On 11/29/21 9:30 AM, J. Bruce Fields wrote:
>>> On Mon, Nov 29, 2021 at 09:13:16AM -0800, dai.ngo@oracle.com wrote:
>>>> Hi Bruce,
>>>>
>>>> On 11/21/21 7:04 PM, dai.ngo@oracle.com wrote:
>>>>> On 11/17/21 4:34 PM, J. Bruce Fields wrote:
>>>>>> On Wed, Nov 17, 2021 at 01:46:02PM -0800, dai.ngo@oracle.com wrote:
>>>>>>> On 11/17/21 9:59 AM, dai.ngo@oracle.com wrote:
>>>>>>>> On 11/17/21 6:14 AM, J. Bruce Fields wrote:
>>>>>>>>> On Tue, Nov 16, 2021 at 03:06:32PM -0800, dai.ngo@oracle.com wrote:
>>>>>>>>>> Just a reminder that this patch is still waiting for your review.
>>>>>>>>> Yeah, I was procrastinating and hoping yo'ud figure out the pynfs
>>>>>>>>> failure for me....
>>>>>>>> Last time I ran 4.0 OPEN18 test by itself and it passed. I will run
>>>>>>>> all OPEN tests together with 5.15-rc7 to see if the problem you've
>>>>>>>> seen still there.
>>>>>>> I ran all tests in nfsv4.1 and nfsv4.0 with courteous and non-courteous
>>>>>>> 5.15-rc7 server.
>>>>>>>
>>>>>>> Nfs4.1 results are the same for both courteous and
>>>>>>> non-courteous server:
>>>>>>>> Of those: 0 Skipped, 0 Failed, 0 Warned, 169 Passed
>>>>>>> Results of nfs4.0 with non-courteous server:
>>>>>>>> Of those: 8 Skipped, 1 Failed, 0 Warned, 577 Passed
>>>>>>> test failed: LOCK24
>>>>>>>
>>>>>>> Results of nfs4.0 with courteous server:
>>>>>>>> Of those: 8 Skipped, 3 Failed, 0 Warned, 575 Passed
>>>>>>> tests failed: LOCK24, OPEN18, OPEN30
>>>>>>>
>>>>>>> OPEN18 and OPEN30 test pass if each is run by itself.
>>>>>> Could well be a bug in the tests, I don't know.
>>>>> The reason OPEN18 failed was because the test timed out waiting for
>>>>> the reply of an OPEN call. The RPC connection used for the test was
>>>>> configured with 15 secs timeout. Note that OPEN18 only fails when
>>>>> the tests were run with 'all' option, this test passes if it's run
>>>>> by itself.
>>>>>
>>>>> With courteous server, by the time OPEN18 runs, there are about 1026
>>>>> courtesy 4.0 clients on the server and all of these clients have opened
>>>>> the same file X with WRITE access. These clients were created by the
>>>>> previous tests. After each test completed, since 4.0 does not have
>>>>> session, the client states are not cleaned up immediately on the
>>>>> server and are allowed to become courtesy clients.
>>>>>
>>>>> When OPEN18 runs (about 20 minutes after the 1st test started), it
>>>>> sends OPEN of file X with OPEN4_SHARE_DENY_WRITE which causes the
>>>>> server to check for conflicts with courtesy clients. The loop that
>>>>> checks 1026 courtesy clients for share/access conflict took less
>>>>> than 1 sec. But it took about 55 secs, on my VM, for the server
>>>>> to expire all 1026 courtesy clients.
>>>>>
>>>>> I modified pynfs to configure the 4.0 RPC connection with 60 seconds
>>>>> timeout and OPEN18 now consistently passed. The 4.0 test results are
>>>>> now the same for courteous and non-courteous server:
>>>>>
>>>>> 8 Skipped, 1 Failed, 0 Warned, 577 Passed
>>>>>
>>>>> Note that 4.1 tests do not suffer this timeout problem because the
>>>>> 4.1 clients and sessions are destroyed after each test completes.
>>>> Do you want me to send the patch to increase the timeout for pynfs?
>>>> or is there any other things you think we should do?
>>> I don't know.
>>>
>>> 55 seconds to clean up 1026 clients is about 50ms per client, which is
>>> pretty slow.  I wonder why.  I guess it's probably updating the stable
>>> storage information.  Is /var/lib/nfs/ on your server backed by a hard
>>> drive or an SSD or something else?
>> My server is a virtualbox VM that has 1 CPU, 4GB RAM and 64GB of hard
>> disk. I think a production system that supports this many clients should
>> have faster CPUs, faster storage.
>>
>>> I wonder if that's an argument for limiting the number of courtesy
>>> clients.
>> I think we might want to treat 4.0 clients a bit different from 4.1
>> clients. With 4.0, every client will become a courtesy client after
>> the client is done with the export and unmounts it.
> It should be safe for a server to purge a client's lease immediately
> if there is no open or lock state associated with it.

In this case, each client has opened files so there are open states
associated with them.

>
> When an NFSv4.0 client unmounts, all files should be closed at that
> point,

I'm not sure pynfs does proper clean up after each subtest, I will
check. There must be state associated with the client in order for
it to become courtesy client.

> so the server can wait for the lease to expire and purge it
> normally. Or am I missing something?

When 4.0 client lease expires and there are still states associated
with the client then the server allows this client to become courtesy
client.

-Dai

>
>
>> Since there is
>> no destroy session/client with 4.0, the courteous server allows the
>> client to be around and becomes a courtesy client. So after awhile,
>> even with normal usage, there will be lots 4.0 courtesy clients
>> hanging around and these clients won't be destroyed until 24hrs
>> later, or until they cause conflicts with other clients.
>>
>> We can reduce the courtesy_client_expiry time for 4.0 clients from
>> 24hrs to 15/20 mins, enough for most network partition to heal?,
>> or limit the number of 4.0 courtesy clients. Or don't support 4.0
>> clients at all which is my preference since I think in general users
>> should skip 4.0 and use 4.1 instead.
>>
>> -Dai
> --
> Chuck Lever
>
>
>