Re: x86 ptep_get_and_clear question

[Ben LaHaise <bcrl@redhat.com>]

On Thu, 15 Feb 2001, Jamie Lokier wrote:

> Ben LaHaise wrote:
> > x86 hardware goes back to the page tables whenever there is an attempt to
> > change the access it has to the pte.  Ie, if it originally accessed the
> > page table for reading, it will go back to the page tables on write.  I
> > believe most hardware that performs accessed/dirty bit updates in hardware
> > behaves the same way.
>
> I think the scenario in question is this:
>
> Processor 2 has recently done some writes, so the dirty bit is set in
> processor 2's TLB.
>
> Processor 1 clears the dirty bit atomically.
>
> Processor 2 does some more writes, and does not check the page table
> because the page is already dirty in its TLB.
>
> Result: The later writes on processor 2 do not mark the page dirty.

Yeah, but the tlb is flushed in those cases (look for flush_tlb_page in
try_to_swap_out).

		-ben

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