writeback: remove nonblocking/encountered_congestion references

This removes more dead code that was somehow missed by commit 0d99519efef
(writeback: remove unused nonblocking and congestion checks). There are
no behavior change except for the removal of two entries from one of the
ext4 tracing interface.

The nonblocking checks in ->writepages are no longer used because the
flusher now prefer to block on get_request_wait() than to skip inodes on
IO congestion. The latter will lead to more seeky IO.

The nonblocking checks in ->writepage are no longer used because it's
redundant with the WB_SYNC_NONE check.

We no long set ->nonblocking in VM page out and page migration, because
a) it's effectively redundant with WB_SYNC_NONE in current code
b) it's old semantic of "Don't get stuck on request queues" is mis-behavior:
that would skip some dirty inodes on congestion and page out others, which
is unfair in terms of LRU age.

Inspired by Christoph Hellwig. Thanks!

Signed-off-by: Wu Fengguang <[e-mail]>
Cc: Theodore Ts'o <[e-mail]>
Cc: David Howells <[e-mail]>
Cc: Sage Weil <[e-mail]>
Cc: Steve French <[e-mail]>
Cc: Chris Mason <[e-mail]>
Cc: Jens Axboe <[e-mail]>
Cc: Christoph Hellwig <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

fs/afs/write.c

···
  */
 int afs_writepage(struct page *page, struct writeback_control *wbc)
 {
-	struct backing_dev_info *bdi = page->mapping->backing_dev_info;
 	struct afs_writeback *wb;
 	int ret;
 
···
 	}
 
 	wbc->nr_to_write -= ret;
-	if (wbc->nonblocking && bdi_write_congested(bdi))
-		wbc->encountered_congestion = 1;
 
 	_leave(" = 0");
 	return 0;
···
 				 struct writeback_control *wbc,
 				 pgoff_t index, pgoff_t end, pgoff_t *_next)
 {
-	struct backing_dev_info *bdi = mapping->backing_dev_info;
 	struct afs_writeback *wb;
 	struct page *page;
 	int ret, n;
···
 
 		wbc->nr_to_write -= ret;
 
-		if (wbc->nonblocking && bdi_write_congested(bdi)) {
-			wbc->encountered_congestion = 1;
-			break;
-		}
-
 		cond_resched();
 	} while (index < end && wbc->nr_to_write > 0);
 
···
 int afs_writepages(struct address_space *mapping,
 		   struct writeback_control *wbc)
 {
-	struct backing_dev_info *bdi = mapping->backing_dev_info;
 	pgoff_t start, end, next;
 	int ret;
 
 	_enter("");
 
-	if (wbc->nonblocking && bdi_write_congested(bdi)) {
-		wbc->encountered_congestion = 1;
-		_leave(" = 0 [congest]");
-		return 0;
-	}
-
 	if (wbc->range_cyclic) {
 		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 &&
-		    !(wbc->nonblocking && wbc->encountered_congestion))
+		if (start > 0 && wbc->nr_to_write > 0 && ret == 0)
 			ret = afs_writepages_region(mapping, wbc, 0, start,
 						    &next);
 		mapping->writeback_index = next;

fs/buffer.c

···
 		 * and kswapd activity, but those code paths have their own
 		 * higher-level throttling.
 		 */
-		if (wbc->sync_mode != WB_SYNC_NONE || !wbc->nonblocking) {
+		if (wbc->sync_mode != WB_SYNC_NONE) {
 			lock_buffer(bh);
 		} else if (!trylock_buffer(bh)) {
 			redirty_page_for_writepage(wbc, page);

fs/ceph/addr.c

···
 				 struct writeback_control *wbc)
 {
 	struct inode *inode = mapping->host;
-	struct backing_dev_info *bdi = mapping->backing_dev_info;
 	struct ceph_inode_info *ci = ceph_inode(inode);
 	struct ceph_fs_client *fsc;
 	pgoff_t index, start, end;
···
 	max_pages_ever = wsize >> PAGE_CACHE_SHIFT;
 
 	pagevec_init(&pvec, 0);
-
-	/* ?? */
-	if (wbc->nonblocking && bdi_write_congested(bdi)) {
-		dout(" writepages congested\n");
-		wbc->encountered_congestion = 1;
-		goto out_final;
-	}
 
 	/* where to start/end? */
 	if (wbc->range_cyclic) {
···
 		rc = 0;  /* vfs expects us to return 0 */
 	ceph_put_snap_context(snapc);
 	dout("writepages done, rc = %d\n", rc);
-out_final:
 	return rc;
 }
 

fs/cifs/file.c

···
 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;
···
 	int rc = 0;
 	int scanned = 0;
 	int xid, long_op;
-
-	/*
-	 * BB: Is this meaningful for a non-block-device file system?
-	 * If it is, we should test it again after we do I/O
-	 */
-	if (wbc->nonblocking && bdi_write_congested(bdi)) {
-		wbc->encountered_congestion = 1;
-		return 0;
-	}
 
 	cifs_sb = CIFS_SB(mapping->host->i_sb);
 

fs/gfs2/meta_io.c

···
 		 * activity, but those code paths have their own higher-level
 		 * throttling.
 		 */
-		if (wbc->sync_mode != WB_SYNC_NONE || !wbc->nonblocking) {
+		if (wbc->sync_mode != WB_SYNC_NONE) {
 			lock_buffer(bh);
 		} else if (!trylock_buffer(bh)) {
 			redirty_page_for_writepage(wbc, page);

fs/nfs/write.c

···
 	nfs_add_stats(inode, NFSIOS_WRITEPAGES, 1);
 
 	nfs_pageio_cond_complete(pgio, page->index);
-	ret = nfs_page_async_flush(pgio, page,
-			wbc->sync_mode == WB_SYNC_NONE ||
-			wbc->nonblocking != 0);
+	ret = nfs_page_async_flush(pgio, page, wbc->sync_mode == WB_SYNC_NONE);
 	if (ret == -EAGAIN) {
 		redirty_page_for_writepage(wbc, page);
 		ret = 0;

fs/reiserfs/inode.c

···
 		/* from this point on, we know the buffer is mapped to a
 		 * real block and not a direct item
 		 */
-		if (wbc->sync_mode != WB_SYNC_NONE || !wbc->nonblocking) {
+		if (wbc->sync_mode != WB_SYNC_NONE) {
 			lock_buffer(bh);
 		} else {
 			if (!trylock_buffer(bh)) {

fs/xfs/linux-2.6/xfs_aops.c

···
 				type = IO_DELAY;
 				flags = BMAPI_ALLOCATE;
 
-				if (wbc->sync_mode == WB_SYNC_NONE &&
-				    wbc->nonblocking)
+				if (wbc->sync_mode == WB_SYNC_NONE)
 					flags |= BMAPI_TRYLOCK;
 			}
 

include/trace/events/ext4.h

···
 		__entry->pages_skipped	= wbc->pages_skipped;
 		__entry->range_start	= wbc->range_start;
 		__entry->range_end	= wbc->range_end;
-		__entry->nonblocking	= wbc->nonblocking;
 		__entry->for_kupdate	= wbc->for_kupdate;
 		__entry->for_reclaim	= wbc->for_reclaim;
 		__entry->range_cyclic	= wbc->range_cyclic;
 		__entry->writeback_index = inode->i_mapping->writeback_index;
 	),
 
-	TP_printk("dev %s ino %lu nr_to_write %ld pages_skipped %ld range_start %llu range_end %llu nonblocking %d for_kupdate %d for_reclaim %d range_cyclic %d writeback_index %lu",
+	TP_printk("dev %s ino %lu nr_to_write %ld pages_skipped %ld "
+		  "range_start %llu range_end %llu "
+		  "for_kupdate %d for_reclaim %d "
+		  "range_cyclic %d writeback_index %lu",
 		  jbd2_dev_to_name(__entry->dev),
 		  (unsigned long) __entry->ino, __entry->nr_to_write,
 		  __entry->pages_skipped, __entry->range_start,
-		  __entry->range_end, __entry->nonblocking,
+		  __entry->range_end,
 		  __entry->for_kupdate, __entry->for_reclaim,
 		  __entry->range_cyclic,
 		  (unsigned long) __entry->writeback_index)

include/trace/events/writeback.h

···
 		__field(long, nr_to_write)
 		__field(long, pages_skipped)
 		__field(int, sync_mode)
-		__field(int, nonblocking)
-		__field(int, encountered_congestion)
 		__field(int, for_kupdate)
 		__field(int, for_background)
 		__field(int, for_reclaim)

mm/migrate.c

···
 		.nr_to_write = 1,
 		.range_start = 0,
 		.range_end = LLONG_MAX,
-		.nonblocking = 1,
 		.for_reclaim = 1
 	};
 	int rc;

mm/vmscan.c

···
 			.nr_to_write = SWAP_CLUSTER_MAX,
 			.range_start = 0,
 			.range_end = LLONG_MAX,
-			.nonblocking = 1,
 			.for_reclaim = 1,
 		};