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

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Date:   Fri, 5 Aug 2022 20:22:46 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Peter Xu <peterx@...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 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