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>

2 files changed, 0 insertions, 2 deletions

diff --git a/mm/migrate.c b/mm/migrate.c
index f8c9bccf2520..d917ac3207f5 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -497,7 +497,6 @@ static int writeout(struct address_space *mapping, struct page *page)
                 .nr_to_write = 1,
                 .range_start = 0,
                 .range_end = LLONG_MAX,
-                .nonblocking = 1,
                 .for_reclaim = 1
         };
         int rc;
diff --git a/mm/vmscan.c b/mm/vmscan.c
index b94c9464f262..6cbc1aac23ae 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -376,7 +376,6 @@ static pageout_t pageout(struct page *page, struct address_space *mapping,
                         .nr_to_write = SWAP_CLUSTER_MAX,
                         .range_start = 0,
                         .range_end = LLONG_MAX,
-                        .nonblocking = 1,
                         .for_reclaim = 1,
                 };