mm: write_cache_pages cleanups

Get rid of some complex expressions from flow control statements, add a comment, remove some duplicate code. Signed-off-by: Nick Piggin <npiggin@suse.de> Cc: Chris Mason <chris.mason@oracle.com> Cc: Dave Chinner <david@fromorbit.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm: write_cache_pages cleanups
Get rid of some complex expressions from flow control statements, add a comment, remove some duplicate code. Signed-off-by: Nick Piggin <npiggin@suse.de> Cc: Chris Mason <chris.mason@oracle.com> Cc: Dave Chinner <david@fromorbit.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Nick Piggin · Linus Torvalds
1 parent 05fe478dd0
Showing 1 changed file with 22 additions and 12 deletions Side-by-side Diff
mm/page-writeback.c
@@ -899,12 +899,15 @@
 	}
 retry:
 	done_index = index;
-	while (!done && (index <= end) &&
-	       (nr_pages = pagevec_lookup_tag(&pvec, mapping, &index,
-					      PAGECACHE_TAG_DIRTY,
-					      min(end - index, (pgoff_t)PAGEVEC_SIZE-1) + 1))) {
-		unsigned i;
+	while (!done && (index <= end)) {
+		int i;
  
+		nr_pages = pagevec_lookup_tag(&pvec, mapping, &index,
+			      PAGECACHE_TAG_DIRTY,
+			      min(end - index, (pgoff_t)PAGEVEC_SIZE-1) + 1);
+		if (nr_pages == 0)
+			break;
+
 		for (i = 0; i < nr_pages; i++) {
 			struct page *page = pvec.pages[i];
  
  
@@ -919,7 +922,16 @@
 			 */
 			lock_page(page);
  
+			/*
+			 * Page truncated or invalidated. We can freely skip it
+			 * then, even for data integrity operations: the page
+			 * has disappeared concurrently, so there could be no
+			 * real expectation of this data interity operation
+			 * even if there is now a new, dirty page at the same
+			 * pagecache address.
+			 */
 			if (unlikely(page->mapping != mapping)) {
+continue_unlock:
 				unlock_page(page);
 				continue;
 			}
  
@@ -930,18 +942,15 @@
 				 * end == -1 in that case.
 				 */
 				done = 1;
-				unlock_page(page);
-				continue;
+				goto continue_unlock;
 			}
  
 			if (wbc->sync_mode != WB_SYNC_NONE)
 				wait_on_page_writeback(page);
  
 			if (PageWriteback(page) ||
-			    !clear_page_dirty_for_io(page)) {
-				unlock_page(page);
-				continue;
-			}
+			    !clear_page_dirty_for_io(page))
+				goto continue_unlock;
  
 			ret = (*writepage)(page, wbc, data);
 			if (unlikely(ret)) {
@@ -964,7 +973,8 @@
  			}
  
 			if (wbc->sync_mode == WB_SYNC_NONE) {
-				if (--wbc->nr_to_write <= 0)
+				wbc->nr_to_write--;
+				if (wbc->nr_to_write <= 0)
 					done = 1;
 			}
 			if (wbc->nonblocking && bdi_write_congested(bdi)) {
...	...	@@ -899,12 +899,15 @@
899	899	}
900	900	retry:
901	901	done_index = index;
902		- while (!done && (index <= end) &&
903		- (nr_pages = pagevec_lookup_tag(&pvec, mapping, &index,
904		- PAGECACHE_TAG_DIRTY,
905		- min(end - index, (pgoff_t)PAGEVEC_SIZE-1) + 1))) {
906		- unsigned i;
	902	+ while (!done && (index <= end)) {
	903	+ int i;
907	904
	905	+ nr_pages = pagevec_lookup_tag(&pvec, mapping, &index,
	906	+ PAGECACHE_TAG_DIRTY,
	907	+ min(end - index, (pgoff_t)PAGEVEC_SIZE-1) + 1);
	908	+ if (nr_pages == 0)
	909	+ break;
	910	+
908	911	for (i = 0; i < nr_pages; i++) {
909	912	struct page *page = pvec.pages[i];
910	913
911	914
...	...	@@ -919,7 +922,16 @@
919	922	*/
920	923	lock_page(page);
921	924
	925	+ /*
	926	+ * Page truncated or invalidated. We can freely skip it
	927	+ * then, even for data integrity operations: the page
	928	+ * has disappeared concurrently, so there could be no
	929	+ * real expectation of this data interity operation
	930	+ * even if there is now a new, dirty page at the same
	931	+ * pagecache address.
	932	+ */
922	933	if (unlikely(page->mapping != mapping)) {
	934	+continue_unlock:
923	935	unlock_page(page);
924	936	continue;
925	937	}
926	938
...	...	@@ -930,18 +942,15 @@
930	942	* end == -1 in that case.
931	943	*/
932	944	done = 1;
933		- unlock_page(page);
934		- continue;
	945	+ goto continue_unlock;
935	946	}
936	947
937	948	if (wbc->sync_mode != WB_SYNC_NONE)
938	949	wait_on_page_writeback(page);
939	950
940	951	if (PageWriteback(page) \|\|
941		- !clear_page_dirty_for_io(page)) {
942		- unlock_page(page);
943		- continue;
944		- }
	952	+ !clear_page_dirty_for_io(page))
	953	+ goto continue_unlock;
945	954
946	955	ret = (*writepage)(page, wbc, data);
947	956	if (unlikely(ret)) {
...	...	@@ -964,7 +973,8 @@
964	973	}
965	974
966	975	if (wbc->sync_mode == WB_SYNC_NONE) {
967		- if (--wbc->nr_to_write <= 0)
	976	+ wbc->nr_to_write--;
	977	+ if (wbc->nr_to_write <= 0)
968	978	done = 1;
969	979	}
970	980	if (wbc->nonblocking && bdi_write_congested(bdi)) {