Re: slowness due to splitting into pages in nfs3svc_decode_writeargs ()

[Bernd Schubert <bernd-schubert@gmx.de>]

On Friday 31 August 2007, J. Bruce Fields wrote:
> On Fri, Aug 31, 2007 at 02:52:15PM -0400, Brian J. Murrell wrote:
> > On Fri, 2007-08-31 at 14:45 -0400, J. Bruce Fields wrote:
> > > Hm.  Any chance this is the same problem?:
> > >
> > > 	http://marc.info/?l=linux-nfs&m=112289652218095&w=2
> >
> > Did this ever land anywhere?
>
> No--I think there were some discussion of problems in the followup
> posts.

To sum up this discussion:

There are two choices to move the data:

1.) To page 2 ... n - this will overwrite nfsv4 at the end of page n.

2.) To page 1 ... n - 1 - this will overwrite the header, thus, all pointers 
to that memory will point to wrong data now.

Seems both aproaches are troublesome and nobody bothered to implement it. Not 
that I much like the idea of data moving at all, but what about

3.) On allocating the pages, allocate one page more than required. After 
filling in page 1, skip page 2 and proceed with page 3.
Now we would have space to properly move the data later on, thus:

memcpy  (page2, page1 + hdr, PAGE_SIZE - hdr_length)
memcpy  (page2 + PAGE_SIZE - hdr_length, page3, hdr_length)

memmove(page3, page3 + hdr_length, PAGE_SIZE - hdr_length)
[...] 


Can you point me to the function assigning the data-block from the network to 
the page-vector?

Thanks,
Bernd

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