linux-kernel - Re: [PATCH v2 1/8] mm: migrate: remove PageTransHuge check in numamigrate_isolate

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Message-ID: <cd3036d5-861e-4be9-b577-eee8d0a61841@huawei.com>
Date:   Mon, 21 Aug 2023 22:41:21 +0800
From:   Kefeng Wang <wangkefeng.wang@...wei.com>
To:     Matthew Wilcox <willy@...radead.org>
CC:     Andrew Morton <akpm@...ux-foundation.org>, <linux-mm@...ck.org>,
        <linux-kernel@...r.kernel.org>, <ying.huang@...el.com>,
        <david@...hat.com>, Zi Yan <ziy@...dia.com>,
        Mike Kravetz <mike.kravetz@...cle.com>, <hughd@...gle.com>
Subject: Re: [PATCH v2 1/8] mm: migrate: remove PageTransHuge check in
 numamigrate_isolate_page()



On 2023/8/21 20:52, Kefeng Wang wrote:
> 
> 
> On 2023/8/21 20:38, Matthew Wilcox wrote:
>> On Mon, Aug 21, 2023 at 07:56:17PM +0800, Kefeng Wang wrote:
>>> Since we begin to convert the numa migration code to use folio, which
>>> could let us to handle arbitrary sizes of folio, so drop assert that
>>> we only support PageTransHuge page(PMD size) when order > 0.
>>
>> Have you looked at the implementation of PageTransHuge()?  Your
>> description doesn't match what the code does.
> 
> oops, not only PMD size...

Please ignore about reply, sorry，I misread， PageTransHuge return true
for head page, and BUG_ON for tail page, and compound_order(page) will
return 0 for tail page, so when begin to convert page to folio, we could
drop this line since it is not useful check for folio.

> 
>>
>>> Suggested-by: Matthew Wilcox (Oracle) <willy@...radead.org>
>>> Signed-off-by: Kefeng Wang <wangkefeng.wang@...wei.com>
>>> ---
>>>   mm/migrate.c | 2 --
>>>   1 file changed, 2 deletions(-)
>>>
>>> diff --git a/mm/migrate.c b/mm/migrate.c
>>> index b7fa020003f3..646d8ee7f102 100644
>>> --- a/mm/migrate.c
>>> +++ b/mm/migrate.c
>>> @@ -2483,8 +2483,6 @@ static int numamigrate_isolate_page(pg_data_t 
>>> *pgdat, struct page *page)
>>>       int nr_pages = thp_nr_pages(page);
>>>       int order = compound_order(page);
>>> -    VM_BUG_ON_PAGE(order && !PageTransHuge(page), page);
>>> -
>>>       /* Do not migrate THP mapped by multiple processes */
>>>       if (PageTransHuge(page) && total_mapcount(page) > 1)
>>>           return 0;
>>> -- 
>>> 2.41.0
>>>
>>>
>>