Re: [PATCH] mm/page_alloc.c: fix a typo

Li Zefan
2008-05-07T01:28:54Z

Andrew Morton wrote:
> On Tue, 06 May 2008 17:50:31 +0800 Li Zefan <lizf@cn.fujitsu.com> wrote:
>
>> Li Zefan wrote:
>>> ---
>> Signed-off-by: Li Zefan <lizf@cn.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.
>
>