| Message ID | 20210416231531.2521383-5-willy@infradead.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | Constify struct page arguments | expand |
On 4/17/21 1:15 AM, Matthew Wilcox (Oracle) wrote: > If you pass a const pointer to compound_head(), you get a const pointer > back; if you pass a mutable pointer, you get a mutable pointer back. Hmm, nice trick. > Also remove an unnecessary forward definition of struct page; we're about > to dereference page->compound_head, so it must already have been defined. Right. > Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org> Reviewed-by: Vlastimil Babka <vbabka@suse.cz> > --- > include/linux/page-flags.h | 10 +++++----- > 1 file changed, 5 insertions(+), 5 deletions(-) > > diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h > index 04a34c08e0a6..d8e26243db25 100644 > --- a/include/linux/page-flags.h > +++ b/include/linux/page-flags.h > @@ -177,17 +177,17 @@ enum pageflags { > > #ifndef __GENERATING_BOUNDS_H > > -struct page; /* forward declaration */ > - > -static inline struct page *compound_head(struct page *page) > +static inline unsigned long _compound_head(const struct page *page) > { > unsigned long head = READ_ONCE(page->compound_head); > > if (unlikely(head & 1)) > - return (struct page *) (head - 1); > - return page; > + return head - 1; > + return (unsigned long)page; > } > > +#define compound_head(page) ((typeof(page))_compound_head(page)) > + > static __always_inline int PageTail(struct page *page) > { > return READ_ONCE(page->compound_head) & 1; >
On 4/17/21 4:45 AM, Matthew Wilcox (Oracle) wrote: > If you pass a const pointer to compound_head(), you get a const pointer > back; if you pass a mutable pointer, you get a mutable pointer back. > Also remove an unnecessary forward definition of struct page; we're about > to dereference page->compound_head, so it must already have been defined. > > Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org> > --- > include/linux/page-flags.h | 10 +++++----- > 1 file changed, 5 insertions(+), 5 deletions(-) > > diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h > index 04a34c08e0a6..d8e26243db25 100644 > --- a/include/linux/page-flags.h > +++ b/include/linux/page-flags.h > @@ -177,17 +177,17 @@ enum pageflags { > > #ifndef __GENERATING_BOUNDS_H > > -struct page; /* forward declaration */ > - > -static inline struct page *compound_head(struct page *page) > +static inline unsigned long _compound_head(const struct page *page) > { > unsigned long head = READ_ONCE(page->compound_head); > > if (unlikely(head & 1)) > - return (struct page *) (head - 1); > - return page; > + return head - 1; > + return (unsigned long)page; > } > > +#define compound_head(page) ((typeof(page))_compound_head(page)) > + > static __always_inline int PageTail(struct page *page) > { > return READ_ONCE(page->compound_head) & 1; > Reviewed-by: Anshuman Khandual <anshuman.khandual@arm.com>
diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h index 04a34c08e0a6..d8e26243db25 100644 --- a/include/linux/page-flags.h +++ b/include/linux/page-flags.h @@ -177,17 +177,17 @@ enum pageflags { #ifndef __GENERATING_BOUNDS_H -struct page; /* forward declaration */ - -static inline struct page *compound_head(struct page *page) +static inline unsigned long _compound_head(const struct page *page) { unsigned long head = READ_ONCE(page->compound_head); if (unlikely(head & 1)) - return (struct page *) (head - 1); - return page; + return head - 1; + return (unsigned long)page; } +#define compound_head(page) ((typeof(page))_compound_head(page)) + static __always_inline int PageTail(struct page *page) { return READ_ONCE(page->compound_head) & 1;
If you pass a const pointer to compound_head(), you get a const pointer back; if you pass a mutable pointer, you get a mutable pointer back. Also remove an unnecessary forward definition of struct page; we're about to dereference page->compound_head, so it must already have been defined. Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org> --- include/linux/page-flags.h | 10 +++++----- 1 file changed, 5 insertions(+), 5 deletions(-)