[PATCH 14/45] writeback: quit on wrap for .range_cyclic (afs)

[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: David Howells <dhowells@xxxxxxxxxx>
Signed-off-by: Wu Fengguang <fengguang.wu@xxxxxxxxx>
---
 fs/afs/write.c |    7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

--- linux.orig/fs/afs/write.c	2009-10-06 23:37:48.000000000 +0800
+++ linux/fs/afs/write.c	2009-10-06 23:38:42.000000000 +0800
@@ -477,8 +477,10 @@ static int afs_writepages_region(struct 
 	do {
 		n = find_get_pages_tag(mapping, &index, PAGECACHE_TAG_DIRTY,
 				       1, &page);
-		if (!n)
+		if (!n) {
+			index = 0;
 			break;
+		}
 
 		_debug("wback %lx", page->index);
 
@@ -551,9 +553,6 @@ int afs_writepages(struct address_space 
 		start = mapping->writeback_index;
 		end = -1;
 		ret = afs_writepages_region(mapping, wbc, start, end, &next);
-		if (start > 0 && wbc->nr_to_write > 0 && ret == 0)
-			ret = afs_writepages_region(mapping, wbc, 0, start,
-						    &next);
 		mapping->writeback_index = next;
 	} else if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX) {
 		end = (pgoff_t)(LLONG_MAX >> PAGE_CACHE_SHIFT);


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