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 <fengguang.wu@intel.com>
Cc: Theodore Ts'o <tytso@mit.edu>
Cc: David Howells <dhowells@redhat.com>
Cc: Sage Weil <sage@newdream.net>
Cc: Steve French <sfrench@samba.org>
Cc: Chris Mason <chris.mason@oracle.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

8 files changed, 6 insertions, 45 deletions

diff --git a/fs/afs/write.c b/fs/afs/write.c
index 722743b152d8..15690bb1d3b5 100644
--- a/fs/afs/write.c
+++ b/fs/afs/write.c
@@ -438,7 +438,6 @@ no_more:
  */
 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;
 
@@ -455,8 +454,6 @@ int afs_writepage(struct page *page, struct writeback_control *wbc)
         }
 
         wbc->nr_to_write -= ret;
-        if (wbc->nonblocking && bdi_write_congested(bdi))
-                wbc->encountered_congestion = 1;
 
         _leave(" = 0");
         return 0;
@@ -469,7 +466,6 @@ static int afs_writepages_region(struct address_space *mapping,
                                  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;
@@ -529,11 +525,6 @@ static int afs_writepages_region(struct address_space *mapping,
 
                 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);
 
@@ -548,24 +539,16 @@ static int afs_writepages_region(struct address_space *mapping,
 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;
diff --git a/fs/buffer.c b/fs/buffer.c
index 7f0b9b083f77..ec21a92e08b4 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -1706,7 +1706,7 @@ static int __block_write_full_page(struct inode *inode, struct page *page,
                  * 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);
diff --git a/fs/ceph/addr.c b/fs/ceph/addr.c
index 51bcc5ce3230..e9c874abc9e1 100644
--- a/fs/ceph/addr.c
+++ b/fs/ceph/addr.c
@@ -591,7 +591,6 @@ static int ceph_writepages_start(struct address_space *mapping,
                                  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;
@@ -633,13 +632,6 @@ static int ceph_writepages_start(struct address_space *mapping,
 
         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) {
                 start = mapping->writeback_index; /* Start from prev offset */
@@ -885,7 +877,6 @@ out:
                 rc = 0;  /* vfs expects us to return 0 */
         ceph_put_snap_context(snapc);
         dout("writepages done, rc = %d\n", rc);
-out_final:
         return rc;
 }
 
diff --git a/fs/cifs/file.c b/fs/cifs/file.c
index 8c81e7b14d53..45af003865d2 100644
--- a/fs/cifs/file.c
+++ b/fs/cifs/file.c
@@ -1303,7 +1303,6 @@ static int cifs_partialpagewrite(struct page *page, unsigned from, unsigned to)
 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;
@@ -1326,15 +1325,6 @@ static int cifs_writepages(struct address_space *mapping,
         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);
 
         /*
diff --git a/fs/gfs2/meta_io.c b/fs/gfs2/meta_io.c
index f3b071f921aa..939739c7b3f9 100644
--- a/fs/gfs2/meta_io.c
+++ b/fs/gfs2/meta_io.c
@@ -55,7 +55,7 @@ static int gfs2_aspace_writepage(struct page *page, struct writeback_control *wb
                  * 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);
diff --git a/fs/nfs/write.c b/fs/nfs/write.c
index 605e292501f4..4c14c17a5276 100644
--- a/fs/nfs/write.c
+++ b/fs/nfs/write.c
@@ -290,9 +290,7 @@ static int nfs_do_writepage(struct page *page, struct writeback_control *wbc, st
         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;
diff --git a/fs/reiserfs/inode.c b/fs/reiserfs/inode.c
index caa758377d66..c1f93896cb53 100644
--- a/fs/reiserfs/inode.c
+++ b/fs/reiserfs/inode.c
@@ -2438,7 +2438,7 @@ static int reiserfs_write_full_page(struct page *page,
                 /* 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)) {
diff --git a/fs/xfs/linux-2.6/xfs_aops.c b/fs/xfs/linux-2.6/xfs_aops.c
index b552f816de15..c9af48fffcd7 100644
--- a/fs/xfs/linux-2.6/xfs_aops.c
+++ b/fs/xfs/linux-2.6/xfs_aops.c
@@ -1139,8 +1139,7 @@ xfs_vm_writepage(
                                 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;
                         }