Re: [PATCH] NFS41: Drop lseg ref before fallthru to MDS

[Benny Halevy <bhalevy@tonian.com>]

On 2011-07-26 12:14, Myklebust, Trond wrote:
>> -----Original Message-----
>> From: Jim Rees [mailto:rees@umich.edu]
>> Sent: Tuesday, July 26, 2011 12:08 PM
>> To: Myklebust, Trond
>> Cc: Peng Tao; tao.peng@emc.com; linux-nfs@vger.kernel.org;
>> bhalevy@tonian.com
>> Subject: Re: [PATCH] NFS41: Drop lseg ref before fallthru to MDS
>>
>> Myklebust, Trond wrote:
>>
>>   > Thanks for your explanation. Is there any plan on how to fix
>>   > pnfs_ld_read/write_done? Basically, we would need an interface
> that
>>   > can redirect the IO to MDS if pnfs_error is set or do all
> necessary
>>   > cleanup work to end read/write if pnfs_error is 0. IMHO, the
>>   > recoalesce logic need to access nfs_pageio_descriptor but we do
> not
>>   > have that information at pnfs_ld_read/write_done.
>>
>>   As far as I can see, the right thing to do is to mark the layout as
>>   invalid and then redirty the page. It should be easy to have fsync()
>>   re-send the pages in this case. These should be extremely rare
>> events,
>>   since we expect to catch most of the pNFS failures when we do the
>> actual
>>   LAYOUTGET in the ->pg_init().
>>
>>   My main worry is for aio/dio where there is no good mechanism for
>>   retrying. I'm still working on that...
>>
>> What do you suggest we do for the current set of patches that add
> block
>> layout to pnfs?
> 
> If you are calling pnfs_ld_read/write_done, then don't change anything:
> it is easier to fix this in one spot rather than several.

Even if we plan on fixing this for the next merge window I think
there's value with the current fix even if it's going to be replaced
with a better fix along the road.

> However someone needs to start working on fixing the code in
> pnfs_ld_read/write_done to do the right thing. If nobody else has the
> cycles, then I can do that but I'd prefer to have someone who can easily
> test the resulting code do it.

I don't have cycles to code this either but I'll be happy to help
with looking at the design and reviewing the implementation.

Benny

> 
> Cheers
>   Trond
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