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    SubjectRe: About get_page for compound page
    On 7/20/07, Peter Zijlstra <peterz@infradead.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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