On 07/10/2019 19:11, Jason Gunthorpe wrote:

On Mon, Oct 07, 2019 at 05:20:30PM +0100, Steven Price wrote:

quoted

On 07/10/2019 17:10, Jason Gunthorpe wrote:

quoted

On Mon, Oct 07, 2019 at 04:38:14PM +0100, Steven Price wrote:

quoted

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.

quoted

quoted

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

quoted

quoted

quoted

 {
 	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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