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SubjectRe: [PATCH 10/75] mm/gup: Remove hpage_pincount_add()
From
On 2/4/22 11:57, Matthew Wilcox (Oracle) wrote:
> It's clearer to call atomic_add() in the callers; the assertions clearly
> can't fire there because they're part of the condition for calling
> atomic_add().
>
> Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
> ---
> mm/gup.c | 33 +++++++++++----------------------
> 1 file changed, 11 insertions(+), 22 deletions(-)

Looks nice.

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

thanks,
--
John Hubbard
NVIDIA

>
> diff --git a/mm/gup.c b/mm/gup.c
> index 923a0d44203c..60168a09d52a 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -29,14 +29,6 @@ struct follow_page_context {
> unsigned int page_mask;
> };
>
> -static void hpage_pincount_add(struct page *page, int refs)
> -{
> - VM_BUG_ON_PAGE(!hpage_pincount_available(page), page);
> - VM_BUG_ON_PAGE(page != compound_head(page), page);
> -
> - atomic_add(refs, compound_pincount_ptr(page));
> -}
> -
> static void hpage_pincount_sub(struct page *page, int refs)
> {
> VM_BUG_ON_PAGE(!hpage_pincount_available(page), page);
> @@ -151,17 +143,17 @@ __maybe_unused struct page *try_grab_compound_head(struct page *page,
> return NULL;
>
> /*
> - * When pinning a compound page of order > 1 (which is what
> - * hpage_pincount_available() checks for), use an exact count to
> - * track it, via hpage_pincount_add/_sub().
> + * When pinning a compound page of order > 1 (which is
> + * what hpage_pincount_available() checks for), use an
> + * exact count to track it.
> *
> - * However, be sure to *also* increment the normal page refcount
> - * field at least once, so that the page really is pinned.
> - * That's why the refcount from the earlier
> + * However, be sure to *also* increment the normal page
> + * refcount field at least once, so that the page really
> + * is pinned. That's why the refcount from the earlier
> * try_get_compound_head() is left intact.
> */
> if (hpage_pincount_available(page))
> - hpage_pincount_add(page, refs);
> + atomic_add(refs, compound_pincount_ptr(page));
> else
> page_ref_add(page, refs * (GUP_PIN_COUNTING_BIAS - 1));
>
> @@ -216,22 +208,19 @@ bool __must_check try_grab_page(struct page *page, unsigned int flags)
> if (flags & FOLL_GET)
> return try_get_page(page);
> else if (flags & FOLL_PIN) {
> - int refs = 1;
> -
> page = compound_head(page);
>
> if (WARN_ON_ONCE(page_ref_count(page) <= 0))
> return false;
>
> /*
> - * Similar to try_grab_compound_head(): even if using the
> - * hpage_pincount_add/_sub() routines, be sure to
> - * *also* increment the normal page refcount field at least
> - * once, so that the page really is pinned.
> + * Similar to try_grab_compound_head(): be sure to *also*
> + * increment the normal page refcount field at least once,
> + * so that the page really is pinned.
> */
> if (hpage_pincount_available(page)) {
> page_ref_add(page, 1);
> - hpage_pincount_add(page, 1);
> + atomic_add(1, compound_pincount_ptr(page));
> } else {
> page_ref_add(page, GUP_PIN_COUNTING_BIAS);
> }

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