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SubjectRe: [PATCH] /proc/PID/smaps: Add PMD migration entry parsing
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.

> --- 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.

> + 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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