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SubjectRe: [PATCH] /proc/PID/smaps: Add PMD migration entry parsing
Date
Andrew Morton <akpm@linux-foundation.org> writes:

> On Tue, 31 Mar 2020 16:56:04 +0800 "Huang, Ying" <ying.huang@intel.com> wrote:
>
>> From: Huang Ying <ying.huang@intel.com>
>>
>> Now, when read /proc/PID/smaps, the PMD migration entry in page table is simply
>> ignored. To improve the accuracy of /proc/PID/smaps, its parsing and processing
>> is added.
>
> It would be helpful to show the before-and-after output in the changelog.

OK.

>> --- a/fs/proc/task_mmu.c
>> +++ b/fs/proc/task_mmu.c
>> @@ -548,8 +548,17 @@ static void smaps_pmd_entry(pmd_t *pmd, unsigned long addr,
>> bool locked = !!(vma->vm_flags & VM_LOCKED);
>> struct page *page;
>>
>> - /* FOLL_DUMP will return -EFAULT on huge zero page */
>> - page = follow_trans_huge_pmd(vma, addr, pmd, FOLL_DUMP);
>> + if (pmd_present(*pmd)) {
>> + /* FOLL_DUMP will return -EFAULT on huge zero page */
>> + page = follow_trans_huge_pmd(vma, addr, pmd, FOLL_DUMP);
>> + } else if (unlikely(is_swap_pmd(*pmd))) {
>> + swp_entry_t entry = pmd_to_swp_entry(*pmd);
>> +
>> + VM_BUG_ON(!is_migration_entry(entry));
>
> I don't think this justifies nuking the kernel. A
> WARN()-and-recover would be better.

Yes. Will change this in the next version.

Best Regards,
Huang, Ying

>> + page = migration_entry_to_page(entry);
>> + } else {
>> + return;
>> + }
>> if (IS_ERR_OR_NULL(page))
>> return;
>> if (PageAnon(page))
>> @@ -578,8 +587,7 @@ static int smaps_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end,
>>
>> ptl = pmd_trans_huge_lock(pmd, vma);
>> if (ptl) {
>> - if (pmd_present(*pmd))
>> - smaps_pmd_entry(pmd, addr, walk);
>> + smaps_pmd_entry(pmd, addr, walk);
>> spin_unlock(ptl);
>> goto out;
>> }

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