linux-kernel - Re: [PATCH 2/2] mm: fix contiguous memmap assumptions about alloc/free pages

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Message-ID: <YkMEyH9QB8MyzW37@casper.infradead.org>
Date:   Tue, 29 Mar 2022 14:08:24 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     Chen Wandun <chenwandun@...wei.com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        akpm@...ux-foundation.org
Subject: Re: [PATCH 2/2] mm: fix contiguous memmap assumptions about
 alloc/free pages

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.

> @@ -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.