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Subject: Re: [PATCH 2/2] mm: fix contiguous memmap assumptions about
 alloc/free pages
To:     Matthew Wilcox <willy@infradead.org>
CC:     <linux-mm@kvack.org>, <linux-kernel@vger.kernel.org>,
        <akpm@linux-foundation.org>
References: <20220329130928.266323-1-chenwandun@huawei.com>
 <20220329130928.266323-3-chenwandun@huawei.com>
 <YkMEyH9QB8MyzW37@casper.infradead.org>
From:   Chen Wandun <chenwandun@huawei.com>
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on 2022/3/29 21:08, Matthew Wilcox wrote:
> On Tue, Mar 29, 2022 at 09:09:28PM +0800, Chen Wandun wrote:
>> +#define page_nth(head, tail)	(page_to_pfn(tail) - page_to_pfn(head))
> Could we avoid reintroducing page_nth()?  It is a terrible name.
how about compound_index ?
>> @@ -1213,7 +1213,7 @@ static int free_tail_pages_check(struct page *head_page, struct page *page)
>>   		ret = 0;
>>   		goto out;
>>   	}
>> -	switch (page - head_page) {
>> +	switch (page_nth(head_page, page)) {
>>   	case 1:
>>   		/* the first tail page: ->mapping may be compound_mapcount() */
>>   		if (unlikely(compound_mapcount(page))) {
> This is the only place you use it.  I'd suggest free_tail_pages_check()
> should take 'i' as its second parameter instead of 'page + i', then
> there's no need to convert back to i.
OK， I will send v2， but I'm not sure whether similar function like 
page_nth is needed elsewhere

>
> .