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

[Christoph Hellwig]

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.