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

[Konstantin Khlebnikov]

On 31/03/2020 11.56, Huang, Ying wrote:
> From: Huang Ying <ying.huang@xxxxxxxxx>
>
> 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.
>
> Signed-off-by: "Huang, Ying" <ying.huang@xxxxxxxxx>
> Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
> Cc: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
> Cc: Zi Yan <ziy@xxxxxxxxxx>
> Cc: Vlastimil Babka <vbabka@xxxxxxx>
> Cc: Alexey Dobriyan <adobriyan@xxxxxxxxx>
> Cc: Michal Hocko <mhocko@xxxxxxxx>
> Cc: Konstantin Khlebnikov <khlebnikov@xxxxxxxxxxxxxx>
> Cc: "JÃrÃme Glisse" <jglisse@xxxxxxxxxx>
> Cc: Yang Shi <yang.shi@xxxxxxxxxxxxxxxxx>
> ---
>   fs/proc/task_mmu.c | 16 ++++++++++++----
>   1 file changed, 12 insertions(+), 4 deletions(-)
>
> diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
> index 8d382d4ec067..b5b3aef8cb3b 100644
> --- 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;

        struct page *page = NULL;

>   
> -	/* 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));
> +		page = migration_entry_to_page(entry);

                if (is_migration_entry(entry))
                        page = migration_entry_to_page(entry);

Seems safer and doesn't add much code.

> +	} 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;
>   	}