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

From: David Hildenbrand <david@redhat.com>
To: Peter Xu <peterx@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 20:22:46 +0200	[thread overview]
Message-ID: <f0d1ebae-f518-9761-f39c-5c1b52f3eebf@redhat.com> (raw)
In-Reply-To: <Yu1eCsMqa641zj5C@xz-m1.local>

On 05.08.22 20:14, Peter Xu wrote:
> 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?

I want something simple to backport. And even with patch #2 in place, as
long as we don't support softdirty tracking, it doesn't make sense to
enable it here as of now.

-- 
Thanks,

David / dhildenb