[PATCH 13/45] writeback: quit on wrap for .range_cyclic (gfs2)

[Wu Fengguang]

Convert wbc.range_cyclic to new behavior: when past EOF, abort writeback
of the inode, which instructs writeback_single_inode() to delay it for a
while if necessary.

It removes one inefficient .range_cyclic IO pattern when writeback_index
wraps:
	submit [10000-10100], (wrap), submit [0-100]
In which the submitted pages may be consisted of two distant ranges.

It also prevents submitting pointless IO for busy overwriters.

CC: Steven Whitehouse <swhiteho@xxxxxxxxxx>
Signed-off-by: Wu Fengguang <fengguang.wu@xxxxxxxxx>
---
 fs/gfs2/aops.c |   16 ++--------------
 1 file changed, 2 insertions(+), 14 deletions(-)

--- linux.orig/fs/gfs2/aops.c	2009-10-06 23:37:48.000000000 +0800
+++ linux/fs/gfs2/aops.c	2009-10-06 23:38:41.000000000 +0800
@@ -287,7 +287,7 @@ static int gfs2_write_jdata_pagevec(stru
 			continue;
 		}
 
-		if (!wbc->range_cyclic && page->index > end) {
+		if (page->index > end) {
 			ret = 1;
 			unlock_page(page);
 			continue;
@@ -340,7 +340,6 @@ static int gfs2_write_cache_jdata(struct
 	int nr_pages;
 	pgoff_t index;
 	pgoff_t end;
-	int scanned = 0;
 	int range_whole = 0;
 
 	pagevec_init(&pvec, 0);
@@ -352,15 +351,12 @@ static int gfs2_write_cache_jdata(struct
 		end = wbc->range_end >> PAGE_CACHE_SHIFT;
 		if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX)
 			range_whole = 1;
-		scanned = 1;
 	}
 
-retry:
 	 while (!done && (index <= end) &&
 		(nr_pages = pagevec_lookup_tag(&pvec, mapping, &index,
 					       PAGECACHE_TAG_DIRTY,
 					       min(end - index, (pgoff_t)PAGEVEC_SIZE-1) + 1))) {
-		scanned = 1;
 		ret = gfs2_write_jdata_pagevec(mapping, wbc, &pvec, nr_pages, end);
 		if (ret)
 			done = 1;
@@ -371,16 +367,8 @@ retry:
 		cond_resched();
 	}
 
-	if (!scanned && !done) {
-		/*
-		 * We hit the last page and there is more work to be done: wrap
-		 * back to the start of the file
-		 */
-		scanned = 1;
+	if (!nr_pages)
 		index = 0;
-		goto retry;
-	}
-
 	if (wbc->range_cyclic || (range_whole && wbc->nr_to_write > 0))
 		mapping->writeback_index = index;
 	return ret;


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