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    SubjectRe: [PATCH v2 17/28] gup: Add gup_put_folio()
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    On 1/9/22 20:23, Matthew Wilcox (Oracle) wrote:
    > Convert put_compound_head() to gup_put_folio() and hpage_pincount_sub()
    > to folio_pincount_sub(). This removes the last call to put_page_refs(),
    > so delete it. Add a temporary put_compound_head() wrapper which will
    > be deleted by the end of this series.
    >
    > Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
    > ---
    > mm/gup.c | 42 ++++++++++++++----------------------------
    > 1 file changed, 14 insertions(+), 28 deletions(-)
    >
    > diff --git a/mm/gup.c b/mm/gup.c
    > index 9e581201d679..719252fa0402 100644
    > --- a/mm/gup.c
    > +++ b/mm/gup.c
    > @@ -45,34 +45,15 @@ static void folio_pincount_add(struct folio *folio, int refs)
    > folio_ref_add(folio, refs * (GUP_PIN_COUNTING_BIAS - 1));
    > }
    >
    > -static int page_pincount_sub(struct page *page, int refs)
    > +static int folio_pincount_sub(struct folio *folio, int refs)

    I just noticed that this return value was a little hard to reason about, which
    prompted me to notice that I'd skipped reviewing patch 10. So I went back
    and added a note there. :)

    Anyway, this one looks good,

    Reviewed-by: John Hubbard <jhubbard@nvidia.com>


    thanks,
    --
    John Hubbard
    NVIDIA

    > {
    > - VM_BUG_ON_PAGE(page != compound_head(page), page);
    > -
    > - if (PageHead(page))
    > - atomic_sub(refs, compound_pincount_ptr(page));
    > + if (folio_test_large(folio))
    > + atomic_sub(refs, folio_pincount_ptr(folio));
    > else
    > refs *= GUP_PIN_COUNTING_BIAS;
    > return refs;
    > }
    >
    > -/* Equivalent to calling put_page() @refs times. */
    > -static void put_page_refs(struct page *page, int refs)
    > -{
    > -#ifdef CONFIG_DEBUG_VM
    > - if (VM_WARN_ON_ONCE_PAGE(page_ref_count(page) < refs, page))
    > - return;
    > -#endif
    > -
    > - /*
    > - * Calling put_page() for each ref is unnecessarily slow. Only the last
    > - * ref needs a put_page().
    > - */
    > - if (refs > 1)
    > - page_ref_sub(page, refs - 1);
    > - put_page(page);
    > -}
    > -
    > /*
    > * Return the folio with ref appropriately incremented,
    > * or NULL if that failed.
    > @@ -171,15 +152,20 @@ struct page *try_grab_compound_head(struct page *page,
    > return &try_grab_folio(page, refs, flags)->page;
    > }
    >
    > -static void put_compound_head(struct page *page, int refs, unsigned int flags)
    > +static void gup_put_folio(struct folio *folio, int refs, unsigned int flags)
    > {
    > if (flags & FOLL_PIN) {
    > - mod_node_page_state(page_pgdat(page), NR_FOLL_PIN_RELEASED,
    > - refs);
    > - refs = page_pincount_sub(page, refs);
    > + node_stat_mod_folio(folio, NR_FOLL_PIN_RELEASED, refs);
    > + refs = folio_pincount_sub(folio, refs);
    > }
    >
    > - put_page_refs(page, refs);
    > + folio_put_refs(folio, refs);
    > +}
    > +
    > +static void put_compound_head(struct page *page, int refs, unsigned int flags)
    > +{
    > + VM_BUG_ON_PAGE(PageTail(page), page);
    > + gup_put_folio((struct folio *)page, refs, flags);
    > }
    >
    > /**
    > @@ -220,7 +206,7 @@ bool __must_check try_grab_page(struct page *page, unsigned int flags)
    > */
    > void unpin_user_page(struct page *page)
    > {
    > - put_compound_head(compound_head(page), 1, FOLL_PIN);
    > + gup_put_folio(page_folio(page), 1, FOLL_PIN);
    > }
    > EXPORT_SYMBOL(unpin_user_page);
    >

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