linux-kernel - Re: [PATCH v2 06/10] mm: memory: use a folio in zap_pte

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Date:   Mon, 6 Nov 2023 23:08:56 +0800
From:   Kefeng Wang <wangkefeng.wang@...wei.com>
To:     Matthew Wilcox <willy@...radead.org>
CC:     Andrew Morton <akpm@...ux-foundation.org>,
        <linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>,
        David Hildenbrand <david@...hat.com>,
        <linux-s390@...r.kernel.org>
Subject: Re: [PATCH v2 06/10] mm: memory: use a folio in zap_pte_range()



On 2023/11/6 22:20, Matthew Wilcox wrote:
> 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.

Sure, I will fix this, also page_try_dup_anon_rmap() for device private
entry in copy_nonpresent_pte of patch5.