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Date:   Mon, 6 Nov 2023 14:20:56 +0000
From:   Matthew Wilcox <willy@infradead.org>
To:     Kefeng Wang <wangkefeng.wang@huawei.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        David Hildenbrand <david@redhat.com>,
        linux-s390@vger.kernel.org
Subject: Re: [PATCH v2 06/10] mm: memory: use a folio in zap_pte_range()
Message-ID: <ZUj2SCML4h7X5TWu@casper.infradead.org>
References: <20231104035522.2418660-1-wangkefeng.wang@huawei.com>
 <20231104035522.2418660-7-wangkefeng.wang@huawei.com>
 <ZUZ9dg4YHZdUKDqO@casper.infradead.org>
 <e3c275c3-e09d-4495-8132-9464133db283@huawei.com>
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On Mon, Nov 06, 2023 at 10:30:59AM +0800, Kefeng Wang wrote:
> On 2023/11/5 1:20, Matthew Wilcox wrote:
> > > -				page_remove_rmap(page, vma, false);
> > > -			put_page(page);
> > > +				page_remove_rmap(&folio->page, vma, false);
> > > +			folio_put(folio);
> > 
> > This is wrong.  If we have a PTE-mapped THP, you'll remove the head page
> > N times instead of removing each of N pages.
> 
> This is device private entry, I suppose that it won't be a THP and large
> folio when check migrate_vma_check_page() and migrate_vma_insert_page(),
> right?

I don't want to leave that kind of booby-trap in the code.  Both places
which currently call page_remove_rmap() should be left as referring to
the page, not the folio.