[pnfs] [PATCH] Increase maximum buffer size for layouts to 4 KB

[Garth Goodson]

Just an FYI, but we will have to deal with the same issues for devices. 
  I know in our case we may end up with some large devices due to 
complicated striping rules.  I also think that the blocks guys may have 
large devices as well (for their volume labels).

-Garth

Benny Halevy wrote:
> Christoph Hellwig wrote:
>> On Tue, Nov 28, 2006 at 12:43:42PM -0500, Dean Hildebrand wrote:
>>> Benny Halevy wrote:
>>>> William A. (Andy) Adamson wrote:
>>>>   
>>>>> hi benny
>>>>>
>>>>> should be ok.
>>>>> are you expecting to have a large number of 4KB layouts? are you 
>>>>> combining a bunch of layout ranges in the 4KB layout return?
>>>>>     
>>>> not necessarily...
>>>> we just have big data structures.
>>>> are we going to keep this static?
>>>> If so I will check what;s the largest size we can anticipate
>>>>
>>>>
>>>>   
>>> The patch below definitely can't go in as is since 4kb layouts will need 
>>> to come off the heap.  I'm assuming you are using a 64 bit machine or 
>>> 8kb stacksize to make this patch work.
>>>
>>> Do we want to
>>> a) malloc 4kb on every layoutget
>>> b) use a layout buffer pool
>>> c) malloc a buffer on every layoutget, but retrieve the size of the 
>>> buffer (the max layout size) from the layout driver
>>> d) other ways?
>> Even 1k on stack is probably yoo much.  So you should dynamially allocate
>> it anyway.  I'm not familar enough with the implementation to know whether
>> it's feasible, but it probably makes sense to control the allocation in
>> the layour driver so we don't allocate more memory than nessecary.
>>
> 
> I agree.  I would go with option c. given the dynamic nature of the
> layout structure.  In our case the layout size depends on how the object
> is laid out and it should be taken from the xdr stream (it could then be
> hashed into buffer pools of different sizes but malloc is doing that
> already...).
> 
> Currently, we do allocate another buffer down at the layout driver and
> we parse and copy the layout coming on the wire into this buffer.
> We can save some memory and valuable bus cycles if we keep the xdr
> buffer and point into it from our internal layout structure, eventually 
> returning it when we free the layout (after return/revoke).  I don't
> know how easy it is to do that...
> 
> Benny
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