Re: new OOM heuristic failure (was: Re: VM: qsbench)

Stephan von Krawczynski
2001-11-02T02:31:10Z

>
> On Fri, 2 Nov 2001, Stephan von Krawczynski wrote:
> >
> > To clarify this one a bit:
> > shrink_cache is thought to do what it says, it is given a number
of
> > pages it should somehow manage to free by shrinking the cache.
What my
> > patch does is go after the _whole_ list to fulfill that.
>
> I would suggest a slight modification: make "max_mapped" grow as the
> priority goes up.
>
> Right now max_mapped is fixed at "nr_pages*10".
>
> You could have something like
>
> max_mapped = nr_pages * 60 / priority;
>
> instead, which might also alleviate the problem with not even
bothering to
> scan much of the inactive list simply because 99% of all pages are
mapped.
>
> That way you don't waste time on looking at the rest of the inactive
list
> until you _need_ to.

Ok. I re-checked the code and found out this approach cannot stand.
the list scan _is_ already exited early when priority is low:

int max_scan = nr_inactive_pages / priority;

while (--max_scan >= 0 && (entry = inactive_list.prev) !=
&inactive_list) {

It will not make big sense to do it again in max_mapped.

On the other hand I am also very sure, that refining:

if (max_mapped==0)
swap_out(priority, gfp_mask, classzone);

return nr_pages;

in the end to:

if (max_mapped==0 && nr_pages>0)
swap_out(priority, gfp_mask, classzone);

return nr_pages;

is a good thing. We don't need swap_out if we gained all the pages
requested, no matter if we _could_ do it or not.

Is there some performance difference in this approach, Lorenzo? I
guess it should.

Regards,
Stephan