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Subject: Re: [PATCH v8 1/2] hugetlb: don't delete vma_lock in hugetlb
 MADV_DONTNEED processing
From:   Nadav Amit <nadav.amit@gmail.com>
In-Reply-To: <Y21xlgG6sxP6q5K9@monkey>
Date:   Thu, 10 Nov 2022 14:22:33 -0800
Cc:     Linux-MM <linux-mm@kvack.org>,
        kernel list <linux-kernel@vger.kernel.org>,
        Naoya Horiguchi <naoya.horiguchi@linux.dev>,
        David Hildenbrand <david@redhat.com>,
        Axel Rasmussen <axelrasmussen@google.com>,
        Mina Almasry <almasrymina@google.com>,
        Peter Xu <peterx@redhat.com>, Rik van Riel <riel@surriel.com>,
        Vlastimil Babka <vbabka@suse.cz>,
        Matthew Wilcox <willy@infradead.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Wei Chen <harperchen1110@gmail.com>, stable@vger.kernel.org
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References: <20221108011910.350887-1-mike.kravetz@oracle.com>
 <20221108011910.350887-2-mike.kravetz@oracle.com>
 <9BB0EA0C-6E7C-462B-8374-5BFEC34E8415@gmail.com> <Y21xlgG6sxP6q5K9@monkey>
To:     Mike Kravetz <mike.kravetz@oracle.com>
Precedence: bulk

On Nov 10, 2022, at 1:48 PM, Mike Kravetz <mike.kravetz@oracle.com> =
wrote:

>>> void unmap_hugepage_range(struct vm_area_struct *vma, unsigned long =
start,
>>> 			  unsigned long end, struct page *ref_page,
>>> 			  zap_flags_t zap_flags)
>>> {
>>> +	struct mmu_notifier_range range;
>>> 	struct mmu_gather tlb;
>>>=20
>>> +	mmu_notifier_range_init(&range, MMU_NOTIFY_UNMAP, 0, vma, =
vma->vm_mm,
>>> +				start, end);
>>> +	adjust_range_if_pmd_sharing_possible(vma, &range.start, =
&range.end);
>>> 	tlb_gather_mmu(&tlb, vma->vm_mm);
>>> +
>>> 	__unmap_hugepage_range(&tlb, vma, start, end, ref_page, =
zap_flags);
>>=20
>> Is there a reason for not using range.start and range.end?
>=20
> After calling adjust_range_if_pmd_sharing_possible, range.start - =
range.end
> could be much greater than the range we actually want to unmap.  The =
range
> gets adjusted to account for pmd sharing if that is POSSIBLE.  It does =
not
> know for sure if we will actually 'unshare a pmd'.
>=20
> I suppose adjust_range_if_pmd_sharing_possible could be modified to =
actually
> check if unmapping will result in unsharing, but it does not do that =
today.

Thanks for the explanation. It=E2=80=99s probably me, but I am still not =
sure that I
understand the the different between __unmap_hugepage_range() using =
(start,
end) and __zap_page_range_single() using (address, range.end). Perhaps =
it
worth a comment in the code?

But anyhow=E2=80=A6 shouldn=E2=80=99t unmap_hugepage_range() call
mmu_notifier_invalidate_range_start()?