linux-kernel - Re: [PATCH] mm/page

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Date:	Wed, 07 May 2008 09:27:27 +0800
From:	Li Zefan <lizf@...fujitsu.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	clameter@....com, LKML <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>
Subject: Re: [PATCH] mm/page_alloc.c: fix a typo

Andrew Morton wrote:
> On Tue, 06 May 2008 17:50:31 +0800 Li Zefan <lizf@...fujitsu.com> wrote:
> 
>> Li Zefan wrote:
>>> ---
>> Signed-off-by: Li Zefan <lizf@...fujitsu.com>
>> ---
>>
>> Sorry for the noise, but the signed-off was eaten. :(
>> Maybe I should leave a blank line before the signed-off.
>>
>> ---
>>
>>  mm/page_alloc.c |    2 +-
>>  1 files changed, 1 insertions(+), 1 deletions(-)
>>
>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>> index bdd5c43..d0ba10d 100644
>> --- a/mm/page_alloc.c
>> +++ b/mm/page_alloc.c
>> @@ -303,7 +303,7 @@ static void destroy_compound_page(struct page *page, unsigned long order)
>>  	for (i = 1; i < nr_pages; i++) {
>>  		struct page *p = page + i;
>>  
>> -		if (unlikely(!PageTail(p) |
>> +		if (unlikely(!PageTail(p) ||
>>  				(p->first_page != page)))
>>  			bad_page(page);
>>  		__ClearPageTail(p);
> 
> I have a vague memory that the "|" was deliberate.  Most of the time,
> "!PageTail" will be false so most of the time we won't take the first

!PageTail will be true if nothing bad happened, corrected me if I'm wrong:

static void prep_compound_page(struct page *page, unsigned long order)
{
	...
	for (i = 1; i < nr_pages; i++) {
		struct page *p = page + i;

		__SetPageTail(p);
		p->first_page = page;
	}
}

> branch so it's probably worth omitting it and always doing the pointer
> comparison.
> 
> It's a somewhat dopey trick and shouldn't have been done without a comment.
> 
> otoh maybe it was a typo.
> 
> 
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