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