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
> >> {
> >> 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;
