Re: [PATCH 10/19] Calculate the preferred zone for allocation only once

Mel Gorman
2009-02-24T17:53:19Z

On Tue, Feb 24, 2009 at 12:31:41PM -0500, Christoph Lameter wrote:
> On Tue, 24 Feb 2009, Mel Gorman wrote:
>
> > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > index 6f26944..074f9a6 100644
> > --- a/mm/page_alloc.c
> > +++ b/mm/page_alloc.c
> > @@ -1399,24 +1399,19 @@ static void zlc_mark_zone_full(struct zonelist *zonelist, struct zoneref *z)
> > */
> > static struct page *
> > get_page_from_freelist(gfp_t gfp_mask, nodemask_t *nodemask, unsigned int order,
> > - struct zonelist *zonelist, int high_zoneidx, int alloc_flags)
> > + struct zonelist *zonelist, int high_zoneidx, int alloc_flags,
> > + struct zone *preferred_zone)
> > {
>
> This gets into a quite a number of parameters now. Pass a structure like in
> vmscan.c?

I considered it, but thought that multiple offsets into structures might
exceed the cost of pushing the parameters onto the stack. I never
actually looked at the generated assembly though to make a proper
assessment.

> Or simplify things to be able to run get_page_from_freelist with
> less parameters? The number of parameters seem to be too high for a
> fastpath function.
>

Which is why I ended up inlining get_page_from_freelist() in V1. It's a rock
and a hard place basically. Passing parameters is expensive, but calculating
the information multiple times is too.

--
Mel Gorman
Part-time Phd Student Linux Technology Center
University of Limerick IBM Dublin Software Lab