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

From: Peter Xu <peterx@redhat.com>
To: David Hildenbrand <david@redhat.com>
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	Andrew Morton <akpm@linux-foundation.org>,
	Mike Kravetz <mike.kravetz@oracle.com>,
	Muchun Song <songmuchun@bytedance.com>,
	Peter Feiner <pfeiner@google.com>,
	"Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
	stable@vger.kernel.org
Subject: Re: [PATCH v1 1/2] mm/hugetlb: fix hugetlb not supporting write-notify
Date: Fri, 5 Aug 2022 14:14:34 -0400	[thread overview]
Message-ID: <Yu1eCsMqa641zj5C@xz-m1.local> (raw)
In-Reply-To: <20220805110329.80540-2-david@redhat.com>

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