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

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Message-ID: <49386753-5984-f708-4153-e9c6de632439@yandex-team.ru>
Date:   Tue, 31 Mar 2020 12:51:38 +0300
From:   Konstantin Khlebnikov <khlebnikov@...dex-team.ru>
To:     "Huang, Ying" <ying.huang@...el.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Andrea Arcangeli <aarcange@...hat.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Zi Yan <ziy@...dia.com>, Vlastimil Babka <vbabka@...e.cz>,
        Alexey Dobriyan <adobriyan@...il.com>,
        Michal Hocko <mhocko@...e.com>,
        Jérôme Glisse <jglisse@...hat.com>,
        Yang Shi <yang.shi@...ux.alibaba.com>
Subject: Re: [PATCH] /proc/PID/smaps: Add PMD migration entry parsing

On 31/03/2020 11.56, Huang, Ying wrote:
> From: Huang Ying <ying.huang@...el.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.
> 
> Signed-off-by: "Huang, Ying" <ying.huang@...el.com>
> Cc: Andrea Arcangeli <aarcange@...hat.com>
> Cc: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> Cc: Zi Yan <ziy@...dia.com>
> Cc: Vlastimil Babka <vbabka@...e.cz>
> Cc: Alexey Dobriyan <adobriyan@...il.com>
> Cc: Michal Hocko <mhocko@...e.com>
> Cc: Konstantin Khlebnikov <khlebnikov@...dex-team.ru>
> Cc: "Jérôme Glisse" <jglisse@...hat.com>
> Cc: Yang Shi <yang.shi@...ux.alibaba.com>
> ---
>   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;
>   	}
>