linux-kernel - Re: [RFC PATCH RESEND 08/28] mm/khugepaged: mark VMA as locked while collapsing a hugepage

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Date:   Tue, 6 Sep 2022 16:43:32 +0200
From:   Laurent Dufour <ldufour@...ux.ibm.com>
To:     Suren Baghdasaryan <surenb@...gle.com>, akpm@...ux-foundation.org
Cc:     michel@...pinasse.org, jglisse@...gle.com, mhocko@...e.com,
        vbabka@...e.cz, hannes@...xchg.org, mgorman@...e.de,
        dave@...olabs.net, willy@...radead.org, liam.howlett@...cle.com,
        peterz@...radead.org, laurent.dufour@...ibm.com,
        paulmck@...nel.org, luto@...nel.org, songliubraving@...com,
        peterx@...hat.com, david@...hat.com, dhowells@...hat.com,
        hughd@...gle.com, bigeasy@...utronix.de, kent.overstreet@...ux.dev,
        rientjes@...gle.com, axelrasmussen@...gle.com, joelaf@...gle.com,
        minchan@...gle.com, kernel-team@...roid.com, linux-mm@...ck.org,
        linux-arm-kernel@...ts.infradead.org,
        linuxppc-dev@...ts.ozlabs.org, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH RESEND 08/28] mm/khugepaged: mark VMA as locked while
 collapsing a hugepage

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@...gle.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,