... cc'ing the arm64 maintainers

On 11/28/2016 01:07 PM, Vlastimil Babka wrote:

On 11/28/2016 05:52 PM, Dave Hansen wrote:

quoted

On 11/24/2016 06:22 AM, Vlastimil Babka wrote:

quoted

On 11/17/2016 01:28 AM, Dave Hansen wrote:

quoted

@@ -702,11 +707,13 @@ static int smaps_hugetlb_range(pte_t *pt
     }
     if (page) {
         int mapcount = page_mapcount(page);
+        unsigned long hpage_size = huge_page_size(hstate_vma(vma));

+        mss->rss_pud += hpage_size;

This hardcoded pud doesn't look right, doesn't the pmd/pud depend on
hpage_size?

Urg, nope.  Thanks for noticing that!  I think we'll need something
along the lines of:

                if (hpage_size == PUD_SIZE)
                        mss->rss_pud += PUD_SIZE;
                else if (hpage_size == PMD_SIZE)
                        mss->rss_pmd += PMD_SIZE;

Sounds better, although I wonder whether there are some weird arches
supporting hugepage sizes that don't match page table levels. I recall
that e.g. MIPS could do arbitrary size, but dunno if the kernel supports
that...

arm64 seems to have pretty arbitrary sizes, and seems to be able to
build them out of multiple hardware PTE sizes.  I think I can fix my
code to handle those:

                if (hpage_size >= PGD_SIZE)
                        mss->rss_pgd += PGD_SIZE;
                else if (hpage_size >= PUD_SIZE)
                        mss->rss_pud += PUD_SIZE;
                else if (hpage_size >= PMD_SIZE)
                        mss->rss_pmd += PMD_SIZE;
                else
                        mss->rss_pte += PAGE_SIZE;

But, I *think* that means that smaps_hugetlb_range() is *currently*
broken for these intermediate arm64 sizes.  The code does:

                if (mapcount >= 2)
                        mss->shared_hugetlb += hpage_size;
                else
                        mss->private_hugetlb += hpage_size;

So I *think* if we may count a hugetlbfs arm64 CONT_PTES page multiple
times, and account hpage_size for *each* of the CONT_PTES.  That would
artificially inflate the smaps output for those pages.

Will / Catalin, is there something I'm missing?

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