Re: [PATCH RFC] 1/2 central workspace for zlib

Jörn Engel
2003-05-31T11:07:30Z

On Sat, 31 May 2003 20:51:04 +1000, James Morris wrote:
> On Fri, 30 May 2003, David S. Miller wrote:
>
> > My understanding is that these are just scratchpads. The contents
> > while a decompress/compress operation is not occuring does not
> > matter.
>
> It depends on how the zlib library is used. The filesystems and crypto
> code use it so that each operation is distinct, although it is possible to
> maintain compression history between operations: PPP does this via a
> sliding compression window, and there are other potential users such as
> ROHC.
>
> One way of addressing this would to allow the user to supply their own
> workspace if compression history needs to be maintained.

Agreed. How much memory is needed for the history? Most of the
workspace or substancially less?

> > So if we have 2 such scratchpads per cpu, one for normal and one for
> > BH context, his idea truly can work and be useful to everyone.
> > It would also be lockless on SMP.
>
> And perhaps implement with a lazy allocation scheme so that these
> scratchpads are only allocated if needed (i.e. a caller does not provide
> its own workspace).

Disagreed. Two scratchpads per cpu won't hurt in the mean case much
and lazy allocation wouldn't improve the worst case either. Keep them
static and simple.

Jörn

--
With a PC, I always felt limited by the software available. On Unix,
I am limited only by my knowledge.
-- Peter J. Schoenster