writeback: introduce wbc.for_background

It will lower the flush priority for NFS, and maybe more in future.

Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
Cc: Trond Myklebust <Trond.Myklebust@netapp.com>
Cc: Jens Axboe <jens.axboe@oracle.com>
Cc: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

3 files changed, 3 insertions, 1 deletions

diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 0306c8e7d6b5..0793961f7699 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -738,6 +738,7 @@ static long wb_writeback(struct bdi_writeback *wb,
                 .sync_mode              = args->sync_mode,
                 .older_than_this        = NULL,
                 .for_kupdate            = args->for_kupdate,
+                .for_background         = args->for_background,
                 .range_cyclic           = args->range_cyclic,
         };
         unsigned long oldest_jif;
diff --git a/fs/nfs/write.c b/fs/nfs/write.c
index 53eb26c16b50..c84b5cc1a943 100644
--- a/fs/nfs/write.c
+++ b/fs/nfs/write.c
@@ -178,7 +178,7 @@ static int wb_priority(struct writeback_control *wbc)
 {
         if (wbc->for_reclaim)
                 return FLUSH_HIGHPRI | FLUSH_STABLE;
-        if (wbc->for_kupdate)
+        if (wbc->for_kupdate || wbc->for_background)
                 return FLUSH_LOWPRI;
         return 0;
 }
diff --git a/include/linux/writeback.h b/include/linux/writeback.h
index 66ebddcff664..705f01fe413a 100644
--- a/include/linux/writeback.h
+++ b/include/linux/writeback.h
@@ -49,6 +49,7 @@ struct writeback_control {
         unsigned nonblocking:1;         /* Don't get stuck on request queues */
         unsigned encountered_congestion:1; /* An output: a queue is full */
         unsigned for_kupdate:1;         /* A kupdate writeback */
+        unsigned for_background:1;      /* A background writeback */
         unsigned for_reclaim:1;         /* Invoked from the page allocator */
         unsigned range_cyclic:1;        /* range_start is cyclic */
         unsigned more_io:1;             /* more io to be dispatched */