linux-kernel - Re: About get_page for compound page

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Message-ID: <ab18d8520707191659l3c176429iee35d00817778711@mail.gmail.com>
Date:	Fri, 20 Jul 2007 07:59:53 +0800
From:	"Fengwei Yin" <yfw.kernel@...il.com>
To:	"Peter Zijlstra" <peterz@...radead.org>
Cc:	LKML <linux-kernel@...r.kernel.org>
Subject: Re: About get_page for compound page

On 7/20/07, Peter Zijlstra <peterz@...radead.org> wrote:
> On Thu, 2007-07-19 at 23:54 +0800, Fengwei Yin wrote:
> > Hi,
> > In get_page(), the parameter page is changed by
> >          page = compound_head(page);
> > if the page is not the first page of compound pages.
> >
> > My question: is this behavior correct?
>
> Yes it is, in general the page state of a compound page is kept in the
> first page of the set.
>
Yes. I know this. But
static inline void get_page(struct page *page)
                                                     ~~~~~~ changed by
this function.
{
         page = compound_head(page);
                    ~~~~~~~~~~~~~~~~~~~~~~~
         VM_BUG_ON(atomic_read(&page->_count) == 0);
         atomic_inc(&page->_count);
}

As I understand, just need update the first page reference count.
Or the caller aware of this bahavior?

Or change it to
static inline void get_page(struct page *page)
{
         struct page *head_page = compound_head(page);
         VM_BUG_ON(atomic_read(&head_page->_count) == 0);
         atomic_inc(&head_page->_count);
}

Regards
Yin, Fengwei
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