[PATCH 11/45] writeback: quit on wrap for .range_cyclic (cifs)

[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: Steve French <sfrench@xxxxxxxxx>
Signed-off-by: Wu Fengguang <fengguang.wu@xxxxxxxxx>
---
 fs/cifs/file.c |   18 ++++--------------
 1 file changed, 4 insertions(+), 14 deletions(-)

--- linux.orig/fs/cifs/file.c	2009-10-06 23:37:49.000000000 +0800
+++ linux/fs/cifs/file.c	2009-10-06 23:38:33.000000000 +0800
@@ -1337,7 +1337,6 @@ static int cifs_partialpagewrite(struct 
 static int cifs_writepages(struct address_space *mapping,
 			   struct writeback_control *wbc)
 {
-	struct backing_dev_info *bdi = mapping->backing_dev_info;
 	unsigned int bytes_to_write;
 	unsigned int bytes_written;
 	struct cifs_sb_info *cifs_sb;
@@ -1349,14 +1348,13 @@ static int cifs_writepages(struct addres
 	int len;
 	int n_iov = 0;
 	pgoff_t next;
-	int nr_pages;
+	int nr_pages = 1;
 	__u64 offset = 0;
 	struct cifsFileInfo *open_file;
 	struct cifsInodeInfo *cifsi = CIFS_I(mapping->host);
 	struct page *page;
 	struct pagevec pvec;
 	int rc = 0;
-	int scanned = 0;
 	int xid, long_op;
 
 	cifs_sb = CIFS_SB(mapping->host->i_sb);
@@ -1390,9 +1388,8 @@ static int cifs_writepages(struct addres
 		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,
@@ -1425,7 +1422,7 @@ retry:
 				break;
 			}
 
-			if (!wbc->range_cyclic && page->index > end) {
+			if (page->index > end) {
 				done = 1;
 				unlock_page(page);
 				break;
@@ -1537,15 +1534,8 @@ retry:
 
 		pagevec_release(&pvec);
 	}
-	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;
 


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