Re: [PATCH v13 19/19] nfs: add FAQ section to Documentation/filesystems/nfs/localio.rst

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> On Aug 25, 2024, at 9:56 PM, NeilBrown <neilb@xxxxxxx> wrote:
> 
> On Sat, 24 Aug 2024, Mike Snitzer wrote:
>> +
>> +6. Why is having the client perform a server-side file OPEN, without
>> +   using RPC, beneficial?  Is the benefit pNFS specific?
>> +
>> +   Avoiding the use of XDR and RPC for file opens is beneficial to
>> +   performance regardless of whether pNFS is used. However adding a
>> +   requirement to go over the wire to do an open and/or close ends up
>> +   negating any benefit of avoiding the wire for doing the I/O itself
>> +   when we’re dealing with small files. There is no benefit to replacing
>> +   the READ or WRITE with a new open and/or close operation that still
>> +   needs to go over the wire.
> 
> I don't think the above is correct.

I struggled with this text too.

I thought the reason we want a server-side file OPEN is so that
proper access authorization, same as would be done on a remote
access, can be done.


> The current code still does a normal NFSv4 OPEN or NFSv3 GETATTR when
> then client opens a file.  Only the READ/WRITE/COMMIT operations are
> avoided.
> 
> While I'm not advocating for an over-the-wire request to map a
> filehandle to a struct nfsd_file*, I don't think you can convincingly
> argue against it without concrete performance measurements.
> 
> NeilBrown

--
Chuck Lever






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