Re: [PATCH 1/9] Revert "pnfs-submit: wave2: remove forgotten layoutreturn struct definitions"

[Peng Tao <bergwolf@gmail.com>]

On Fri, Dec 17, 2010 at 1:37 AM, Benny Halevy <bhalevy@panasas.com> wrote:
> On 2010-12-16 19:21, Peng Tao wrote:
>> Hi, Benny,
>>
>> On Thu, Dec 16, 2010 at 3:26 PM, Benny Halevy <bhalevy@panasas.com> wrote:
>>> On 2010-12-15 22:24, Trond Myklebust wrote:
>>>> On Wed, 2010-12-15 at 14:31 -0500, Trond Myklebust wrote:
>>>>> On Wed, 2010-12-15 at 20:51 +0200, Benny Halevy wrote:
>>>>
>>>>>> Eventually, when CB_LAYOUTRECALL is clear to go sending the LAYOUTRETURN
>>>>>> or replying with CB_NOMATCHING_LAYOUT (assuming no I/O error to report
>>>>>> for pnfs-obj) should be equivalent [note: need errata to clarify the
>>>>>> resulting stateid after NOMATCHING_LAYOUT].
>>>>>> Is this the serialization "crap" you're talking about?
>>>>>> What makes checking the conditions for returning NFS4ERR_DELAY to
>>>>>> CB_LAYOUTRECALL so different from implementing a barrier and doing the
>>>>>> returns asynchronously with the CB_LAYOUTRECALL?
>>>>>
>>>>> "CB_LAYOUTRECALL request processing MUST be processed in "seqid" order
>>>>> at all times." (section 12.5.3).
>>>>>
>>>>> In other words, you cannot just 'do the returns asynchronously': the
>>>>> CB_LAYOUTRECALL requests are required by the protocol to be processed in
>>>>> order, which means that you must serialise those LAYOUTRETURN calls to
>>>>> ensure that they all happen in the order the wretched server expects.
>>>>
>>>> BTW: one consequence of the way the protocol was written is that you
>>>> can't just throw out a LAYOUTRETURN for the entire file if the server
>>>> just recalls a segment. Instead, you have to first return the segment,
>>>> then send the LAYOUTRETURN for the entire file.
>>>>
>>>
>>> It is true that the protocol requires the return of the exact recalled range
>>> but why can't the client do return the whole file before returning the recalled
>>> range?
>> Just for clarification, do you mean that after client returns more
>> than server recalls, clients still has to do an echoing LAYOUTRETURN?
>> It is barely overhead...
>> Why would server require some behavior like that?
>>
>
> The reason for that in the protocol was to provide a simple way to
> complete a CB_LAYOUTRECALL "meta operation" when the client returns
> the layout in smaller ranges than recalled. We overlooked this case
> of the client returning a range containing the returned range.
> which is easier to deal with, with further stateid related functionality
> we introduced after specifying how layout recall initially worked...
I see it. Thanks. The behavior is clearly defined in section 18.44.3.
And only in the subset returning case, client has to do a matching
layoutreturn to complete CB_LAYOUTRECALL.

>
> Benny
>
>>>
>>>> That part of the protocol is just one insane idea after another...
>>>>
>>>
>>> This was done to ensure that the server and client are in-sync after a
>>> CB_LAYOUTRECALL.  I agree that returning the whole layout thus resetting
>>> the layout state achieves the same goal and we should consider allowing it
>>> in the next version.
>>>
>>> Benny
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>>
>>
>>
>



-- 
Thanks,
-Bergwolf