[PATCH v2 1/9] mm/rmap: recompute pgoff for huge page

[Joonsoo Kim]

We have to recompute pgoff if the given page is huge, since result based
on HPAGE_SIZE is not approapriate for scanning the vma interval tree, as
shown by commit 36e4f20af833 ("hugetlb: do not use vma_hugecache_offset()
for vma_prio_tree_foreach") and commit 369a713e ("rmap: recompute pgoff
for unmapping huge page").

To handle both the cases, normal page for page cache and hugetlb page,
by same way, we can use compound_page(). It returns 0 on non-compound page
and it also returns proper value on compound page.

Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>

diff --git a/mm/rmap.c b/mm/rmap.c
index 55c8b8d..20c1a0d 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1508,7 +1508,7 @@ static int try_to_unmap_anon(struct page *page, enum ttu_flags flags)
 static int try_to_unmap_file(struct page *page, enum ttu_flags flags)
 {
 	struct address_space *mapping = page->mapping;
-	pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
+	pgoff_t pgoff = page->index << compound_order(page);
 	struct vm_area_struct *vma;
 	int ret = SWAP_AGAIN;
 	unsigned long cursor;
@@ -1516,9 +1516,6 @@ static int try_to_unmap_file(struct page *page, enum ttu_flags flags)
 	unsigned long max_nl_size = 0;
 	unsigned int mapcount;
 
-	if (PageHuge(page))
-		pgoff = page->index << compound_order(page);
-
 	mutex_lock(&mapping->i_mmap_mutex);
 	vma_interval_tree_foreach(vma, &mapping->i_mmap, pgoff, pgoff) {
 		unsigned long address = vma_address(page, vma);
@@ -1708,7 +1705,7 @@ static int rmap_walk_file(struct page *page, int (*rmap_one)(struct page *,
 		struct vm_area_struct *, unsigned long, void *), void *arg)
 {
 	struct address_space *mapping = page->mapping;
-	pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
+	pgoff_t pgoff = page->index << compound_order(page);
 	struct vm_area_struct *vma;
 	int ret = SWAP_AGAIN;
 
-- 
1.7.9.5

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