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Date:   Mon, 21 Nov 2022 16:24:04 +0300
From:   "Kirill A. Shutemov" <kirill@shutemov.name>
To:     Hugh Dickins <hughd@google.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Matthew Wilcox <willy@infradead.org>,
        David Hildenbrand <david@redhat.com>,
        Vlastimil Babka <vbabka@suse.cz>, Peter Xu <peterx@redhat.com>,
        Yang Shi <shy828301@gmail.com>,
        John Hubbard <jhubbard@nvidia.com>,
        Mike Kravetz <mike.kravetz@oracle.com>,
        Sidhartha Kumar <sidhartha.kumar@oracle.com>,
        Muchun Song <songmuchun@bytedance.com>,
        Miaohe Lin <linmiaohe@huawei.com>,
        Naoya Horiguchi <naoya.horiguchi@linux.dev>,
        Mina Almasry <almasrymina@google.com>,
        James Houghton <jthoughton@google.com>,
        Zach O'Keefe <zokeefe@google.com>,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCH 3/3] mm,thp,rmap: clean up the end of
 __split_huge_pmd_locked()
Message-ID: <20221121132404.sebpecbc5joto7h7@box.shutemov.name>
References: <5f52de70-975-e94f-f141-543765736181@google.com>
 <c4b8485b-1f26-1a5f-bdf-c6c22611f610@google.com>
 <2f4afe60-40d2-706c-af21-914fbbbd164@google.com>
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On Fri, Nov 18, 2022 at 01:16:20AM -0800, Hugh Dickins wrote:
> It's hard to add a page_add_anon_rmap() into __split_huge_pmd_locked()'s
> HPAGE_PMD_NR set_pte_at() loop, without wincing at the "freeze" case's
> HPAGE_PMD_NR page_remove_rmap() loop below it.
> 
> It's just a mistake to add rmaps in the "freeze" (insert migration entries
> prior to splitting huge page) case: the pmd_migration case already avoids
> doing that, so just follow its lead.  page_add_ref() versus put_page()
> likewise.  But why is one more put_page() needed in the "freeze" case?
> Because it's removing the pmd rmap, already removed when pmd_migration
> (and freeze and pmd_migration are mutually exclusive cases).
> 
> Signed-off-by: Hugh Dickins <hughd@google.com>

Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>

-- 
  Kiryl Shutsemau / Kirill A. Shutemov