Re: [RFC] Page table sharing

From: Linus Torvalds (torvalds@transmeta.com)
Date: Tue Feb 19 2002 - 12:29:04 EST


On Tue, 19 Feb 2002, Daniel Phillips wrote:
> >
> > At that point you might as well make the TLB shootdown global (ie you keep
> > track of a mask of CPU's whose TLB's you want to kill, and any pmd that
> > has count > 1 just makes that mask be "all CPU's").
>
> How do we know when to do the global tlb flush?

See above.

Basically, the algorithm is:

        invalidate_cpu_mask = 0;

        .. for each page swapped out ..

                pte = ptep_get_and_clear(ptep);
                save_pte_and_mm(pte_page(pte));
                mask = mm->cpu_vm_mask;
                if (page_count(pmd_page) > 1)
                        mask = ~0UL;
                invalidate_cpu_mask |= mask;

and then at the end you just do

        flush_tlb_cpus(invalidate_cpu_mask);
        for_each_page_saved() {
                free_page(page);
        }

(yeah, yeah, add cache coherency etc).

                Linus

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