linux-kernel - Re: [PATCH v5 1/6] userfaultfd: convert mfill_atomic_pte

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Date:   Sat, 8 Apr 2023 12:42:11 +0800
From:   "zhangpeng (AS)" <zhangpeng362@...wei.com>
To:     Mike Kravetz <mike.kravetz@...cle.com>
CC:     <linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>,
        <akpm@...ux-foundation.org>, <willy@...radead.org>,
        <sidhartha.kumar@...cle.com>, <vishal.moola@...il.com>,
        <muchun.song@...ux.dev>, <wangkefeng.wang@...wei.com>,
        <sunnanyong@...wei.com>
Subject: Re: [PATCH v5 1/6] userfaultfd: convert mfill_atomic_pte_copy() to
 use a folio

On 2023/4/7 5:31, Mike Kravetz wrote:

> On 03/31/23 17:39, Peng Zhang wrote:
>> From: ZhangPeng <zhangpeng362@...wei.com>
>>
>> Call vma_alloc_folio() directly instead of alloc_page_vma() and convert
>> page_kaddr to kaddr in mfill_atomic_pte_copy(). Removes several calls to
>> compound_head().
>>
>> Signed-off-by: ZhangPeng <zhangpeng362@...wei.com>
>> Reviewed-by: Sidhartha Kumar <sidhartha.kumar@...cle.com>
>> ---
>>   mm/userfaultfd.c | 33 +++++++++++++++++----------------
>>   1 file changed, 17 insertions(+), 16 deletions(-)
> Looks good,
>
> Reviewed-by: Mike Kravetz <mike.kravetz@...cle.com>
>
>>   	} else {
>> -		page = *pagep;
>> +		folio = page_folio(*pagep);
>> +		VM_BUG_ON_FOLIO(folio_test_large(folio), folio);
>>   		*pagep = NULL;
>>   	}
> However, I am still unsure about the reason for adding the VM_BUG_ON_FOLIO
> here.

VM_BUG_ON_FOLIO was added to ensure that folio is a single-page folio.
However, the folio corresponding to the foliop is always a single-page
folio. We just don't need this check. I'll drop VM_BUG_ON_FOLIO.

Thanks for your review.

Best Regards,
Peng