Re: [PATCH] total_free_shortage() using zone_free_shortage()

[Linus Torvalds]

On Mon, 6 Aug 2001, Marcelo Tosatti wrote:
>
> The following patch changes total_free_shortage() to use
> zone_free_shortage() to calculate the sum of perzone free shortages.

Marcelo, the patch looks ok per se, but I think the real _problem_ is that
you did the same mistake in do_page_launder() as you originally did in the
VM scanning.

The code should NOT use

	if (zone && !zone_free_shortage(page->zone))
		.. don't touch ..

because that is completely nonsensical anyway.

As with the VM scanning code, it should do

	if (zone_free_plenty(page->zone))
		.. don't touch ..

and you should make

	zone_free_plenty(zone)
	{
		return zone->free_pages + zone->inactive_clean_pages > zone->max_free_pages;
	}

and

	zone_free_shortage(zone)
	{
		return zone->free_pages + zone->inactive_clean_pages < zone->low_free_pages;
	}

Note the anti-hysteresis by using max_free_pages vs min_free_pages.

This will clean up the code (remove those silly "zone as a boolean"), and
I bet it will behave better too with less of a spike in behaviour around
"max_free_pages".

			Linus