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SubjectRe: [PATCH v11 14/22] mm: pagewalk: Add 'depth' parameter to pte_hole
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On 07/10/2019 19:11, Jason Gunthorpe wrote:
> On Mon, Oct 07, 2019 at 05:20:30PM +0100, Steven Price wrote:
>> On 07/10/2019 17:10, Jason Gunthorpe wrote:
>>> On Mon, Oct 07, 2019 at 04:38:14PM +0100, Steven Price wrote:
>>>> diff --git a/mm/hmm.c b/mm/hmm.c
>>>> index 902f5fa6bf93..34fe904dd417 100644
>>>> +++ b/mm/hmm.c
>>>> @@ -376,7 +376,7 @@ static void hmm_range_need_fault(const struct hmm_vma_walk *hmm_vma_walk,
>>>> }
>>>>
>>>> static int hmm_vma_walk_hole(unsigned long addr, unsigned long end,
>>>> - struct mm_walk *walk)
>>>> + __always_unused int depth, struct mm_walk *walk)
>>>
>>> It this __always_unused on function arguments something we are doing
>>> now?
>>
>> $ git grep __always_unused | wc -l
>> 191
>>
>> It's elsewhere in the kernel tree. It seems like a good way of both
>> documenting and silencing compiler warnings. But I'm open to other
>> suggestions.
>
> The normal kernel build doesn't generate warnings for unused function
> parameters because there are alot of false positives, IIRC. So, seems
> weird to see things like this.
>
>>> Can we have negative depth? Should it be unsigned?
>>
>> As per the documentation added in this patch:
>>
>> * @pte_hole: if set, called for each hole at all levels,
>> * depth is -1 if not known, 0:PGD, 1:P4D, 2:PUD, 3:PMD
>> * 4:PTE. Any folded depths (where PTRS_PER_P?D is equal
>> * to 1) are skipped.
>>
>> So it's signed to allow "-1" in the cases where pte_hole is called
>> without knowing the actual depth. This is used in the function
>> walk_page_test() because it don't walk the actual page tables, but is
>> called on a VMA instead. This means that there may not be a single depth
>> for the range provided.
>
> So are the depth values below OK? I would have expected -1 by this
> definition

Good spot - that indeed was very sloppy of me. In these cases the value
is ignored, but -1 would indeed have been a better value to use. I'll
fix that up.

Thanks,

Steve

>>>> {
>>>> struct hmm_vma_walk *hmm_vma_walk = walk->private;
>>>> struct hmm_range *range = hmm_vma_walk->range;
>>>> @@ -564,7 +564,7 @@ static int hmm_vma_walk_pmd(pmd_t *pmdp,
>>>> again:
>>>> pmd = READ_ONCE(*pmdp);
>>>> if (pmd_none(pmd))
>>>> - return hmm_vma_walk_hole(start, end, walk);
>>>> + return hmm_vma_walk_hole(start, end, 0, walk);
>>>>
>>>> if (thp_migration_supported() && is_pmd_migration_entry(pmd)) {
>>>> bool fault, write_fault;
>>>> @@ -666,7 +666,7 @@ static int hmm_vma_walk_pud(pud_t *pudp, unsigned long start, unsigned long end,
>>>> again:
>>>> pud = READ_ONCE(*pudp);
>>>> if (pud_none(pud))
>>>> - return hmm_vma_walk_hole(start, end, walk);
>>>> + return hmm_vma_walk_hole(start, end, 0, walk);
>>>>
>>>> if (pud_huge(pud) && pud_devmap(pud)) {
>>>> unsigned long i, npages, pfn;
>>>> @@ -674,7 +674,7 @@ static int hmm_vma_walk_pud(pud_t *pudp, unsigned long start, unsigned long end,
>>>> bool fault, write_fault;
>>>>
>>>> if (!pud_present(pud))
>>>> - return hmm_vma_walk_hole(start, end, walk);
>>>> + return hmm_vma_walk_hole(start, end, 0, walk);
>>>>
>>>> i = (addr - range->start) >> PAGE_SHIFT;
>>>> npages = (end - addr) >> PAGE_SHIFT;
>
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> linux-arm-kernel@lists.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
>

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