linux-kernel - Re: [PATCH v2 2/9] mm/vmscan: remove unneeded can_split_huge

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Message-ID: <e60591a0-7a87-db07-1234-1ee19e1c90d0@huawei.com>
Date:   Tue, 12 Apr 2022 11:14:40 +0800
From:   Miaohe Lin <linmiaohe@...wei.com>
To:     Christoph Hellwig <hch@...radead.org>
CC:     <akpm@...ux-foundation.org>, <ying.huang@...el.com>,
        <songmuchun@...edance.com>, <willy@...radead.org>,
        <linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 2/9] mm/vmscan: remove unneeded can_split_huge_page
 check

On 2022/4/11 22:18, Christoph Hellwig wrote:
> On Sat, Apr 09, 2022 at 05:34:53PM +0800, Miaohe Lin wrote:
>> We don't need to check can_split_folio() because folio_maybe_dma_pinned()
>> is checked before. It will avoid the long term pinned pages to be swapped
>> out. And we can live with short term pinned pages. Without can_split_folio
>> checking we can simplify the code. Also activate_locked can be changed to
>> keep_locked as it's just short term pinning.
>>
>> Suggested-by: Huang, Ying <ying.huang@...el.com>
>> Signed-off-by: Miaohe Lin <linmiaohe@...wei.com>
>> ---
>>  mm/vmscan.c | 22 ++++++++--------------
>>  1 file changed, 8 insertions(+), 14 deletions(-)
>>
>> diff --git a/mm/vmscan.c b/mm/vmscan.c
>> index 4a76be47bed1..01f5db75a507 100644
>> --- a/mm/vmscan.c
>> +++ b/mm/vmscan.c
>> @@ -1711,20 +1711,14 @@ static unsigned int shrink_page_list(struct list_head *page_list,
>>  					goto keep_locked;
>>  				if (folio_maybe_dma_pinned(folio))
>>  					goto keep_locked;
>> -				if (PageTransHuge(page)) {
>> -					/* cannot split THP, skip it */
>> -					if (!can_split_folio(folio, NULL))
>> -						goto activate_locked;
>> -					/*
>> -					 * Split pages without a PMD map right
>> -					 * away. Chances are some or all of the
>> -					 * tail pages can be freed without IO.
>> -					 */
>> -					if (!folio_entire_mapcount(folio) &&
>> -					    split_folio_to_list(folio,
>> -								page_list))
>> -						goto activate_locked;
>> -				}
>> +				/*
>> +				 * Split pages without a PMD map right
>> +				 * away. Chances are some or all of the
>> +				 * tail pages can be freed without IO.
>> +				 */
> 
> This could use more of the line length and be more readable:
> 
> 				/*
> 				 * Split pages without a PMD map right away.
> 				 * Chances are some or all of the tail pages
> 				 * can be freed without IO.
> 				 */
> 

Looks better.

>> +				if (PageTransHuge(page) && !folio_entire_mapcount(folio) &&
> 
> Please put the folio_entire_mapcoun ont a separate line to make this a
> bit more redable.

Will do in next version. Many thanks for your comment!

> .
>