On Wed, 2012-06-27 at 23:15 +0200, Peter Zijlstra wrote:
>
> S390 doesn't need a TLB flush after ptep_get_and_clear_full() and
> before __tlb_remove_page() because its ptep_get_and_clear*() family
> already does a full TLB invalidate. Therefore force it to use
> tlb_fast_mode.
On that.. ptep_get_and_clear() says:
/*
* This is hard to understand. ptep_get_and_clear and ptep_clear_flush
* both clear the TLB for the unmapped pte. The reason is that
* ptep_get_and_clear is used in common code (e.g. change_pte_range)
* to modify an active pte. The sequence is
* 1) ptep_get_and_clear
* 2) set_pte_at
* 3) flush_tlb_range
* On s390 the tlb needs to get flushed with the modification of the pte
* if the pte is active. The only way how this can be implemented is to
* have ptep_get_and_clear do the tlb flush. In exchange flush_tlb_range
* is a nop.
*/
I think there is another way, arch_{enter,leave}_lazy_mmu_mode() seems
to wrap these sites so you can do as SPARC64 and PPC do and batch
through there.
That should save a number of TLB invalidates..
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