linux-kernel - [PATCH -next] mm/rmap: calculate page offset when needed

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Date:	Fri, 07 Nov 2014 11:34:17 -0800
From:	Davidlohr Bueso <dave@...olabs.net>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	Davidlohr Bueso <dave@...olabs.net>
Subject: [PATCH -next] mm/rmap: calculate page offset when needed

Call page_to_pgoff() to get the page offset once we are
sure we actually need it, and any very obvious initial
function checks have passed. Trivial micro-optimization,
and potentially save some cycles.

Signed-off-by: Davidlohr Bueso <dbueso@...e.de>
---
 mm/rmap.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/mm/rmap.c b/mm/rmap.c
index a5e9cc6..e3354b2 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1633,7 +1633,7 @@ static struct anon_vma *rmap_walk_anon_lock(struct page *page,
 static int rmap_walk_anon(struct page *page, struct rmap_walk_control *rwc)
 {
 	struct anon_vma *anon_vma;
-	pgoff_t pgoff = page_to_pgoff(page);
+	pgoff_t pgoff;
 	struct anon_vma_chain *avc;
 	int ret = SWAP_AGAIN;
 
@@ -1641,6 +1641,7 @@ static int rmap_walk_anon(struct page *page, struct rmap_walk_control *rwc)
 	if (!anon_vma)
 		return ret;
 
+	pgoff = page_to_pgoff(page);
 	anon_vma_interval_tree_foreach(avc, &anon_vma->rb_root, pgoff, pgoff) {
 		struct vm_area_struct *vma = avc->vma;
 		unsigned long address = vma_address(page, vma);
@@ -1674,7 +1675,7 @@ static int rmap_walk_anon(struct page *page, struct rmap_walk_control *rwc)
 static int rmap_walk_file(struct page *page, struct rmap_walk_control *rwc)
 {
 	struct address_space *mapping = page->mapping;
-	pgoff_t pgoff = page_to_pgoff(page);
+	pgoff_t pgoff;
 	struct vm_area_struct *vma;
 	int ret = SWAP_AGAIN;
 
@@ -1689,6 +1690,7 @@ static int rmap_walk_file(struct page *page, struct rmap_walk_control *rwc)
 	if (!mapping)
 		return ret;
 
+	pgoff = page_to_pgoff(page);
 	i_mmap_lock_read(mapping);
 	vma_interval_tree_foreach(vma, &mapping->i_mmap, pgoff, pgoff) {
 		unsigned long address = vma_address(page, vma);
-- 
1.8.4.5


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