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SubjectRE: [RFC] Demand faulting for large pages
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Adam Litke wrote on Friday, August 05, 2005 8:22 AM
> Below is a patch to implement demand faulting for huge pages. The main
> motivation for changing from prefaulting to demand faulting is so that
> huge page allocations can follow the NUMA API. Currently, huge pages
> are allocated round-robin from all NUMA nodes.

Chen, Kenneth W wrote on Friday, August 05, 2005 2:34 PM
> Spurious WARN_ON. Calls to hugetlb_pte_fault() is conditioned upon
> if (is_vm_hugetlb_page(vma))
>
> ....
>
> Broken here. Return VM_FAULT_SIGBUS when *pte is present?? Why
> can't you move all the logic into hugetlb_pte_fault and simply call
> it directly from handle_mm_fault?


I'm wondering has this patch ever been tested? More broken bits:
in arch/i386/mm/hugetlbpage.c:huge_pte_offset - with demand paging,
you can't unconditionally walk the page table without checking
existence of pud and pmd.

I haven't looked closely at recent change in free_pgtables(), but
we used to have a need to scrub old pmd mapping before allocate one
for hugetlb pte on x86. You have to do that in huge_pte_alloc(),
I'm specifically concerned with arch/i386/mm/hugetlbpage.c:huge_pte_alloc()

- Ken

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