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    SubjectRe: [PATCH v3 04/12] mm: introduce page_ref_sub_return()
    On Fri, Jan 31, 2020 at 07:40:21PM -0800, John Hubbard wrote:
    > An upcoming patch requires subtracting a large chunk of refcounts from
    > a page, and checking what the resulting refcount is. This is a little
    > different than the usual "check for zero refcount" that many of the
    > page ref functions already do. However, it is similar to a few other
    > routines that (like this one) are generally useful for things such as
    > 1-based refcounting.
    >
    > Add page_ref_sub_return(), that subtracts a chunk of refcounts
    > atomically, and returns an atomic snapshot of the result.
    >
    > Signed-off-by: John Hubbard <jhubbard@nvidia.com>
    > ---
    > include/linux/page_ref.h | 10 ++++++++++
    > 1 file changed, 10 insertions(+)
    >
    > diff --git a/include/linux/page_ref.h b/include/linux/page_ref.h
    > index 14d14beb1f7f..b9cbe553d1e7 100644
    > --- a/include/linux/page_ref.h
    > +++ b/include/linux/page_ref.h
    > @@ -102,6 +102,16 @@ static inline void page_ref_sub(struct page *page, int nr)
    > __page_ref_mod(page, -nr);
    > }
    >
    > +static inline int page_ref_sub_return(struct page *page, int nr)
    > +{
    > + int ret = atomic_sub_return(nr, &page->_refcount);
    > +
    > + if (page_ref_tracepoint_active(__tracepoint_page_ref_mod))
    > + __page_ref_mod(page, -nr);

    Shouldn't it be __page_ref_mod_and_return() and relevant tracepoint?

    > +
    > + return ret;
    > +}
    > +
    > static inline void page_ref_inc(struct page *page)
    > {
    > atomic_inc(&page->_refcount);
    > --
    > 2.25.0
    >

    --
    Kirill A. Shutemov

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