linux-kernel - Re: [RFC PATCH 3/5] mm proc/task_mmu.c: add soft dirty pte checks for hugetlb

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Date:   Wed, 17 Feb 2021 14:35:50 -0500
From:   Peter Xu <peterx@...hat.com>
To:     Mike Kravetz <mike.kravetz@...cle.com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        linux-s390@...r.kernel.org, shu wang <malate_wangshu@...mail.com>,
        Axel Rasmussen <axelrasmussen@...gle.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Alexey Dobriyan <adobriyan@...il.com>,
        Matthew Wilcox <willy@...radead.org>,
        Michel Lespinasse <walken@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [RFC PATCH 3/5] mm proc/task_mmu.c: add soft dirty pte checks
 for hugetlb

On Wed, Feb 10, 2021 at 04:03:20PM -0800, Mike Kravetz wrote:
> Pagemap was only using the vma flag PM_SOFT_DIRTY for hugetlb vmas.
> This is insufficient.  Check the individual pte entries.
> 
> Signed-off-by: Mike Kravetz <mike.kravetz@...cle.com>
> ---
>  fs/proc/task_mmu.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
> index 602e3a52884d..829b35016aaa 100644
> --- a/fs/proc/task_mmu.c
> +++ b/fs/proc/task_mmu.c
> @@ -1507,6 +1507,10 @@ static int pagemap_hugetlb_range(pte_t *ptep, unsigned long hmask,
>  		flags |= PM_SOFT_DIRTY;
>  
>  	pte = huge_ptep_get(ptep);
> +
> +	if (huge_pte_soft_dirty(pte))
> +		flags |= PM_SOFT_DIRTY;

Should this be put into pte_present() chunk below?  Since I feel like we'd need
huge_pte_swp_soft_dirty() for !pte_present().  Say, _PAGE_SOFT_DIRTY and
_PAGE_SWP_SOFT_DIRTY can be different.

> +
>  	if (pte_present(pte)) {
>  		struct page *page = pte_page(pte);
>  
> -- 
> 2.29.2
> 

-- 
Peter Xu