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SubjectRe: [PATCH 7/8] mm: thp: Use more portable PMD clearing sequenece in zap_huge_pmd().
On Tue, Oct 02, 2012 at 06:27:41PM -0400, David Miller wrote:
>
> Invalidation sequences are handled in various ways on various
> architectures.
>
> One way, which sparc64 uses, is to let the set_*_at() functions
> accumulate pending flushes into a per-cpu array. Then the
> flush_tlb_range() et al. calls process the pending TLB flushes.
>
> In this regime, the __tlb_remove_*tlb_entry() implementations are
> essentially NOPs.
>
> The canonical PTE zap in mm/memory.c is:
>
> ptent = ptep_get_and_clear_full(mm, addr, pte,
> tlb->fullmm);
> tlb_remove_tlb_entry(tlb, pte, addr);
>
> With a subsequent tlb_flush_mmu() if needed.
>
> Mirror this in the THP PMD zapping using:
>
> orig_pmd = pmdp_get_and_clear(tlb->mm, addr, pmd);
> page = pmd_page(orig_pmd);
> tlb_remove_pmd_tlb_entry(tlb, pmd, addr);
>
> And we properly accomodate TLB flush mechanims like the one described
> above.

Thanks for the explanation.

Reviewed-by: Andrea Arcangeli <aarcange@redhat.com>


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