From mboxrd@z Thu Jan  1 00:00:00 1970
From: npiggin@suse.de
Subject: [patch 5/9] mm: write_cache_pages cleanups
Date: Wed, 29 Oct 2008 01:47:20 +1100
Message-ID: <20081028145734.321394000@nick.local0.net>
References: <20081028144715.683011000@suse.de>
Cc: linux-fsdevel@vger.kernel.org, Dave Chinner <david@fromorbit.com>,
	Chris Mason <chris.mason@oracle.com>
To: akpm@linux-foundation.org
Return-path: <linux-fsdevel-owner@vger.kernel.org>
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	Tue, 28 Oct 2008 11:01:13 -0400
Content-Disposition: inline; filename=mm-wcp-cleanup.patch
Sender: linux-fsdevel-owner@vger.kernel.org
List-ID: <linux-fsdevel.vger.kernel.org>

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>
---
Index: linux-2.6/mm/page-writeback.c
===================================================================
--- linux-2.6.orig/mm/page-writeback.c
+++ linux-2.6/mm/page-writeback.c
@@ -899,11 +899,14 @@ int write_cache_pages(struct address_spa
 	}
 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)) {

--