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Date: Wed, 8 May 2024 12:52:53 -0300
From: Jason Gunthorpe <jgg@nvidia.com>
To: Zi Yan <ziy@nvidia.com>
Cc: Lance Yang <ioworker0@gmail.com>, Alistair Popple <apopple@nvidia.com>,
	akpm@linux-foundation.org, willy@infradead.org, sj@kernel.org,
	maskray@google.com, ryan.roberts@arm.com, david@redhat.com,
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	linux-mm@kvack.org, linux-kernel@vger.kernel.org,
	Baolin Wang <baolin.wang@linux.alibaba.com>
Subject: Re: [PATCH v4 2/3] mm/rmap: integrate PMD-mapped folio splitting
 into pagewalk loop
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On Wed, May 08, 2024 at 10:56:34AM -0400, Zi Yan wrote:

> Lance is improving try_to_unmap_one() to support unmapping PMD THP as a whole,
> so he moves split_huge_pmd_address() inside while (page_vma_mapped_walk(&pvmw))
> and after mmu_notifier_invalidate_range_start() as split_huge_pmd_locked()
> and does not include the mmu notifier ops inside split_huge_pmd_address().
> I wonder if that could cause issues, since the mmu_notifier_invalidate_range_start()
> before the while loop only has range of the original address and
> split huge pmd can affect the entire PMD address range and these two ranges
> might not be the same.

That does not sound entirely good..

I suppose it depends on what split does, if the MM page table has the
same translation before and after split then perhaps no invalidation
is even necessary.

Jason