Catalin Marinas <catalin.marinas@xxxxxxx> writes:
> On Thu, Aug 10, 2017 at 06:09:02PM +0100, Punit Agrawal wrote:
>> diff --git a/arch/arm64/mm/hugetlbpage.c b/arch/arm64/mm/hugetlbpage.c
>> index d3a6713048a2..09e79785c019 100644
>> --- a/arch/arm64/mm/hugetlbpage.c
>> +++ b/arch/arm64/mm/hugetlbpage.c
>> @@ -210,6 +210,7 @@ pte_t *huge_pte_offset(struct mm_struct *mm,
>> pgd_t *pgd;
>> pud_t *pud;
>> pmd_t *pmd;
>> + pte_t *pte;
>>
>> pgd = pgd_offset(mm, addr);
>> pr_debug("%s: addr:0x%lx pgd:%p\n", __func__, addr, pgd);
>> @@ -217,19 +218,29 @@ pte_t *huge_pte_offset(struct mm_struct *mm,
>> return NULL;
>>
>> pud = pud_offset(pgd, addr);
>> - if (pud_none(*pud))
>> + if (pud_none(*pud) && sz != PUD_SIZE)
>> return NULL;
>> /* swap or huge page */
>> if (!pud_present(*pud) || pud_huge(*pud))
>> return (pte_t *)pud;
>> /* table; check the next level */
>
> So if sz == PUD_SIZE and we have pud_none(*pud) == true, it returns the
> pud. Isn't this different from what you proposed for the generic
> huge_pte_offset()? [1]
I think I missed this case in the generic version.
As hugetlb_fault() deals with p*d_none() entries by calling
hugetlb_no_page(), the thinking was that returning the p*d saves us an
extra round trip by avoiding the call to huge_pte_alloc().
>
>>
>> + if (sz == CONT_PMD_SIZE)
>> + addr &= CONT_PMD_MASK;
>> +
>> pmd = pmd_offset(pud, addr);
>> - if (pmd_none(*pmd))
>> + if (pmd_none(*pmd) &&
>> + !(sz == PMD_SIZE || sz == CONT_PMD_SIZE))
>> return NULL;
>
> Again, if sz == PMD_SIZE, you no longer return NULL. The generic
> proposal in [1] looks like:
>
> if (pmd_none(*pmd))
> return NULL;
>
> and that's even when sz == PMD_SIZE.
>
> Anyway, I think we need to push for [1] again to be accepted before we
> go ahead with these changes.
[1] is already queued in Andrew's tree. I'll send an update - hopefully
it can be picked up for the next merge.
>
> [1] http://lkml.kernel.org/r/20170725154114.24131-2-punit.agrawal@xxxxxxx
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