Re: Hot/cold allocation -- swsusp can not handle hot pages

[William Lee Irwin III]

On Sun, Nov 03, 2002 at 09:08:09PM +0100, Pavel Machek wrote:
> "big-picture" should be in Documentation/swsusp.txt...
> *Should* be :-(. I need to copy all used memory, to make sure my
> snapshot is atomic.
> Copying works by looking at what is allocated, counting needed pages,
> allocating 'directory' for them, allocating memory for copies, and
> actually copying.
> When I suddenly find I have less data to copy than I thought, it
> screws up the code.

Why don't we just mark PG_nosave in page->flags and stuff order in
page->index (or elsewhere) for you and then you can safely walk
the zone->zone_mem_map? A single pass of marking up-front should
be a bit quicker than searching the lists for a list head at every
page, and also something more maintainable/comprehensible: we can
basically know what we're dealing with and do a kind of "shutdown"
of the stuff for you:

static void empty_pageset(struct zone *zone, struct per_cpu_pages *pcp)
{
	pcp->batch = pcp->low = pcp->high = 1;
	pcp->count -= free_pages_bulk(zone, pcp->batch, &pcp->list, 0);
}

static void empty_cpu_pages(void *unused)
{
	struct zone *zone;
	unsigned long flags;
	int cpu;

	cpu = get_cpu();
	local_irq_save(flags);

	for_each_zone(zone) {
		empty_pcp(zone, &zone->pageset[cpu].pcp[0]);
		empty_pcp(zone, &zone->pageset[cpu].pcp[1]);
	}

	local_irq_restore(flags);
	put_cpu();
}

static void shootdown_per_cpu_pages(void)
{
	smp_call_function(empty_cpu_pages, NULL, 0, 1);
	empty_cpu_pages(NULL);
}

void suspend_mark_free_pages(void)
{
	struct zone *zone;
	struct free_area *area;
	struct page *page;
	unsigned long flags;
	int order;

	shootdown_per_cpu_pages();

	for_each_zone(zone) {
		spin_lock_irqsave(&zone->lock, flags);
		for (order = 0; order < MAX_ORDER; ++order) {
			area = &zone->free_area[order];
			list_for_each_entry(page, &area->free_list, list) {
				SetPageNosave(page);
				/* if ->index clashes, use flag bits */
				page->index = order;
			}
		}
		spin_unlock_irqrestore(&zone->lock, flags);
	}
}

Then you can just do

	if (PageNosave(page))
		pfn += 1 << page->index;

in kernel/suspend.c and everybody's happy, no?

Bill