On 11/28/2016 10:39 PM, Dave Hansen wrote:
> ... 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:
>>> On 11/24/2016 06:22 AM, Vlastimil Babka wrote:
>>>> On 11/17/2016 01:28 AM, Dave Hansen wrote:
>>>>> @@ -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.
Hmm IIUC walk_hugetlb_range() will call the smaps_hugetlb_range()
callback once per hugepage, not once per "pte", no? See
hugetlb_entry_end(). In that case the current code should be OK and
yours would undercount?
> Will / Catalin, is there something I'm missing?
>
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