[PATCH v2 2/3] mm: Introduce page_shift()

[Matthew Wilcox <willy@infradead.org>]

From: "Matthew Wilcox (Oracle)" <willy@infradead.org>

Replace PAGE_SHIFT + compound_order(page) with the new page_shift()
function.  Minor improvements in readability.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
---
 arch/powerpc/mm/book3s64/iommu_api.c | 7 ++-----
 drivers/vfio/vfio_iommu_spapr_tce.c  | 2 +-
 include/linux/mm.h                   | 6 ++++++
 3 files changed, 9 insertions(+), 6 deletions(-)

diff --git a/arch/powerpc/mm/book3s64/iommu_api.c b/arch/powerpc/mm/book3s64/iommu_api.c
index b056cae3388b..56cc84520577 100644
--- a/arch/powerpc/mm/book3s64/iommu_api.c
+++ b/arch/powerpc/mm/book3s64/iommu_api.c
@@ -129,11 +129,8 @@ static long mm_iommu_do_alloc(struct mm_struct *mm, unsigned long ua,
 		 * Allow to use larger than 64k IOMMU pages. Only do that
 		 * if we are backed by hugetlb.
 		 */
-		if ((mem->pageshift > PAGE_SHIFT) && PageHuge(page)) {
-			struct page *head = compound_head(page);
-
-			pageshift = compound_order(head) + PAGE_SHIFT;
-		}
+		if ((mem->pageshift > PAGE_SHIFT) && PageHuge(page))
+			pageshift = page_shift(compound_head(page));
 		mem->pageshift = min(mem->pageshift, pageshift);
 		/*
 		 * We don't need struct page reference any more, switch
diff --git a/drivers/vfio/vfio_iommu_spapr_tce.c b/drivers/vfio/vfio_iommu_spapr_tce.c
index 8ce9ad21129f..1883fd2901b2 100644
--- a/drivers/vfio/vfio_iommu_spapr_tce.c
+++ b/drivers/vfio/vfio_iommu_spapr_tce.c
@@ -190,7 +190,7 @@ static bool tce_page_is_contained(struct mm_struct *mm, unsigned long hpa,
 	 * a page we just found. Otherwise the hardware can get access to
 	 * a bigger memory chunk that it should.
 	 */
-	return (PAGE_SHIFT + compound_order(compound_head(page))) >= page_shift;
+	return page_shift(compound_head(page)) >= page_shift;
 }
 
 static inline bool tce_groups_attached(struct tce_container *container)
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 899dfcf7c23d..64762559885f 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -811,6 +811,12 @@ static inline unsigned long page_size(struct page *page)
 	return PAGE_SIZE << compound_order(page);
 }
 
+/* Returns the number of bits needed for the number of bytes in a page */
+static inline unsigned int page_shift(struct page *page)
+{
+	return PAGE_SHIFT + compound_order(page);
+}
+
 void free_compound_page(struct page *page);
 
 #ifdef CONFIG_MMU
-- 
2.20.1