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Date:   Tue, 6 Sep 2022 16:43:32 +0200
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Subject: Re: [RFC PATCH RESEND 08/28] mm/khugepaged: mark VMA as locked while
 collapsing a hugepage
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To:     Suren Baghdasaryan <surenb@google.com>, akpm@linux-foundation.org
Cc:     michel@lespinasse.org, jglisse@google.com, mhocko@suse.com,
        vbabka@suse.cz, hannes@cmpxchg.org, mgorman@suse.de,
        dave@stgolabs.net, willy@infradead.org, liam.howlett@oracle.com,
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        hughd@google.com, bigeasy@linutronix.de, kent.overstreet@linux.dev,
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        minchan@google.com, kernel-team@android.com, linux-mm@kvack.org,
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References: <20220901173516.702122-1-surenb@google.com>
 <20220901173516.702122-9-surenb@google.com>
From:   Laurent Dufour <ldufour@linux.ibm.com>
In-Reply-To: <20220901173516.702122-9-surenb@google.com>
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Le 01/09/2022 à 19:34, Suren Baghdasaryan a écrit :
> Protect VMA from concurrent page fault handler while modifying it in
> collapse_huge_page.

Is the goal to protect changes in the anon_vma structure?

AFAICS, the vma it self is not impacted here, only the anon_vma and the
PMD/PTE are touched, and they have their own protection mechanism, isn't it?

> 
> Signed-off-by: Suren Baghdasaryan <surenb@google.com>
> ---
>  mm/khugepaged.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> index 01f71786d530..030680633989 100644
> --- a/mm/khugepaged.c
> +++ b/mm/khugepaged.c
> @@ -1072,6 +1072,7 @@ static void collapse_huge_page(struct mm_struct *mm,
>  	if (mm_find_pmd(mm, address) != pmd)
>  		goto out_up_write;
>  
> +	vma_mark_locked(vma);
>  	anon_vma_lock_write(vma->anon_vma);
>  
>  	mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, NULL, mm,