[PATCHv3 20/41] mm: make write_cache_pages() work on huge pages

["Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>]

We writeback whole huge page a time. Let's adjust iteration this way.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
---
 include/linux/mm.h      |  1 +
 include/linux/pagemap.h |  1 +
 mm/page-writeback.c     | 17 ++++++++++++-----
 3 files changed, 14 insertions(+), 5 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index ef815b9cd426..44e55d1c8e41 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1054,6 +1054,7 @@ struct address_space *page_file_mapping(struct page *page)
  */
 static inline pgoff_t page_index(struct page *page)
 {
+	page = compound_head(page);
 	if (unlikely(PageSwapCache(page)))
 		return page_private(page);
 	return page->index;
diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index a84f11a672f0..4d6e9aec2d1f 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -518,6 +518,7 @@ static inline void wait_on_page_locked(struct page *page)
  */
 static inline void wait_on_page_writeback(struct page *page)
 {
+	page = compound_head(page);
 	if (PageWriteback(page))
 		wait_on_page_bit(page, PG_writeback);
 }
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index f4cd7d8005c9..6390c9488e29 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -2242,7 +2242,7 @@ retry:
 			 * mapping. However, page->index will not change
 			 * because we have a reference on the page.
 			 */
-			if (page->index > end) {
+			if (page_to_pgoff(page) > end) {
 				/*
 				 * can't be range_cyclic (1st pass) because
 				 * end == -1 in that case.
@@ -2251,7 +2251,12 @@ retry:
 				break;
 			}
 
-			done_index = page->index;
+			done_index = page_to_pgoff(page);
+			if (PageTransCompound(page)) {
+				index = round_up(index + 1, HPAGE_PMD_NR);
+				i += HPAGE_PMD_NR -
+					done_index % HPAGE_PMD_NR - 1;
+			}
 
 			lock_page(page);
 
@@ -2263,7 +2268,7 @@ retry:
 			 * even if there is now a new, dirty page at the same
 			 * pagecache address.
 			 */
-			if (unlikely(page->mapping != mapping)) {
+			if (unlikely(page_mapping(page) != mapping)) {
 continue_unlock:
 				unlock_page(page);
 				continue;
@@ -2301,7 +2306,8 @@ continue_unlock:
 					 * not be suitable for data integrity
 					 * writeout).
 					 */
-					done_index = page->index + 1;
+					done_index = compound_head(page)->index
+						+ hpage_nr_pages(page);
 					done = 1;
 					break;
 				}
@@ -2313,7 +2319,8 @@ continue_unlock:
 			 * keep going until we have written all the pages
 			 * we tagged for writeback prior to entering this loop.
 			 */
-			if (--wbc->nr_to_write <= 0 &&
+			wbc->nr_to_write -= hpage_nr_pages(page);
+			if (wbc->nr_to_write <= 0 &&
 			    wbc->sync_mode == WB_SYNC_NONE) {
 				done = 1;
 				break;
-- 
2.9.3

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