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>

1 files changed, 22 insertions, 12 deletions

diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 5edca676e2c3..c3fb38b1ea43 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -899,11 +899,14 @@ int write_cache_pages(struct address_space *mapping,
         }
 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 @@ retry:
                          */
                         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 @@ retry:
                                  * 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 @@ retry:
                         }
 
                         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)) {