linux-kernel - Re: [PATCH v1 1/2] mm/hugetlb: fix hugetlb not supporting write-notify

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Message-ID: <Yu1eCsMqa641zj5C@xz-m1.local>
Date:   Fri, 5 Aug 2022 14:14:34 -0400
From:   Peter Xu <peterx@...hat.com>
To:     David Hildenbrand <david@...hat.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Muchun Song <songmuchun@...edance.com>,
        Peter Feiner <pfeiner@...gle.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        stable@...r.kernel.org
Subject: Re: [PATCH v1 1/2] mm/hugetlb: fix hugetlb not supporting
 write-notify

On Fri, Aug 05, 2022 at 01:03:28PM +0200, David Hildenbrand wrote:
> diff --git a/mm/mmap.c b/mm/mmap.c
> index 61e6135c54ef..462a6b0344ac 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -1683,6 +1683,13 @@ int vma_wants_writenotify(struct vm_area_struct *vma, pgprot_t vm_page_prot)
>  	if ((vm_flags & (VM_WRITE|VM_SHARED)) != ((VM_WRITE|VM_SHARED)))
>  		return 0;
>  
> +	/*
> +	 * Hugetlb does not require/support writenotify; especially, it does not
> +	 * support softdirty tracking.
> +	 */
> +	if (is_vm_hugetlb_page(vma))
> +		return 0;

I'm kind of confused here..  you seems to be fixing up soft-dirty for
hugetlb but here it's explicitly forbidden.

Could you explain a bit more on why this patch is needed if (assume
there'll be a working) patch 2 being provided?

Thanks,

-- 
Peter Xu