Re: About the free page pool

Andrew Morton
2002-09-02T21:21:42Z

Rik van Riel wrote:
>
> On Mon, 2 Sep 2002, Andrew Morton wrote:
>
> > > How important is it to maintain a list of free pages? That is, how
> > > critical is it that there be some pool of free pages from which the only
> > > bookkeeping required is the removal of that page from the free list.
> >
> > There are several reasons, all messy.
>
> [snip]
>
> > It's feasible. It'd take some work. Probably it would best be implemented
> > via a third list. That list would be protected by an IRQ-safe lock,
>
> I don't think we need to bother with the IRQ-safe part.
>
> It's much simpler if we just do:
>
> 1) have a normal free list, but have it smaller ...
> say, between zone->pages_min and zone->pages_low
>
> 2) if the free pages drop below the low water mark,
> have either a normal allocator or a kernel thread
> refill it to the high water mark, from the clean
> pages list
>
> 3) have the free+clean target set to something higher,
> say zone->pages_high ... we could even tune this
> automatically, if we run out of free+clean pages too
> often kswapd should probably try to keep more pages
> clean
>
> What do you think, would this work?

Well, I'm at a bit of a loss to understand what the objective
of all this is. Is it so that we can effectively increase the
cache size, by not "wasting" all that free memory?