Re: vm lock contention reduction

[Andrew Morton <akpm@zip.com.au>]

Rik van Riel wrote:
> 
> On Thu, 4 Jul 2002, Andrew Morton wrote:
> 
> > If the machine is instead full of anon pages then everything is still
> > crap because the page reclaim code is scanning zillions of pages and not
> > doing much useful with them.
> 
> This is something that can be fixed with rmap, because the
> kernel _will_ be able to do something useful with the anon
> pages.

I think that would be quite useful - we just need to be sure that if the
pages aren't added to swapcache we should park them up on the active list
out of the way.

The refill_inactive() logic in 2.5.24 seems a bit wonky at present.
In here:

        ratio = (unsigned long)nr_pages * ps.nr_active /
                                ((ps.nr_inactive | 1) * 2);
        refill_inactive(ratio);

`ratio' tends to evaluate to zero if you have a ton of inactive
or pagecache pages.  So the VM is not recirculating old pages
off the inactive list at all.

I changed it to add 1 to ratio.  Also to only call refill_inactive
when the number-to-process reaches 32 pages - the kernel tends
to settle into steady states where it's calling refill_inactive
for just one or two pages, which is a waste of CPU.

Didn't make much observable difference.

> Now we just need to get Arjan to tune the O(1) page launder
> thing he was looking at ;)

We keep seeing mysterious references to this. What is the idea
behind it?

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