linux-kernel - Re: [PATCH v5 5/6] mm: convert copy_user_huge_page() to copy_user

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Message-ID: <35123e7f-093a-ef90-0c14-befa67bd565c@huawei.com>
Date:   Sat, 8 Apr 2023 12:42:42 +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 5/6] mm: convert copy_user_huge_page() to
 copy_user_folio()

On 2023/4/7 7:55, Mike Kravetz wrote:

> On 03/31/23 17:39, Peng Zhang wrote:
>> From: ZhangPeng <zhangpeng362@...wei.com>
>>
>> Replace copy_user_huge_page() with copy_user_folio(). copy_user_folio()
>> does the same as copy_user_huge_page(), but takes in folios instead of
>> pages. Convert copy_user_gigantic_page() to take in folios.
>> Remove pages_per_huge_page from copy_user_folio(), because we can get
>> that from folio_nr_pages(dst).
>>
>> Signed-off-by: ZhangPeng <zhangpeng362@...wei.com>
>> ---
>>   include/linux/mm.h |  7 +++----
>>   mm/hugetlb.c       | 10 ++++------
>>   mm/memory.c        | 28 ++++++++++++++--------------
>>   3 files changed, 21 insertions(+), 24 deletions(-)
> No technical problems with the patch, but ...
>>   
>> @@ -5847,15 +5847,15 @@ static void copy_subpage(unsigned long addr, int idx, void *arg)
>>   			   addr, copy_arg->vma);
>>   }
>>   
>> -void copy_user_huge_page(struct page *dst, struct page *src,
>> -			 unsigned long addr_hint, struct vm_area_struct *vma,
>> -			 unsigned int pages_per_huge_page)
>> +void copy_user_folio(struct folio *dst, struct folio *src,
>> +		      unsigned long addr_hint, struct vm_area_struct *vma)
>>   {
>> +	unsigned int pages_per_huge_page = folio_nr_pages(dst);
>>   	unsigned long addr = addr_hint &
>>   		~(((unsigned long)pages_per_huge_page << PAGE_SHIFT) - 1);
>>   	struct copy_subpage_arg arg = {
>> -		.dst = dst,
>> -		.src = src,
>> +		.dst = &dst->page,
>> +		.src = &src->page,
>>   		.vma = vma,
>>   	};
>>   
> I seem to recall that Matthew suggested changing the function name to
> copy_user_folio.  My only concern is that the name now sounds like a
> general purpose routine for copying folios.  It certainly would work
> for a single page folio, but there is a bunch of unnecessary overhead
> in that case.
>
> That makes me think there should perhaps be an optimized path for single
> page folios that just does copy_user_highpage().  But, the argument addr_hint
> does not make much sense in the single page folio case.  So, I am not
> sure if I agree with leaving large/huge out of the function name.
>
> Just wondering if Matthew has any additional thoughts?

Agreed. In my opinion, it's better to leave large/huge out of the
function name.
Also wondering if Matthew has any additional considerations?

Best Regards,
Peng