[PATCH] nfs: fix congestion control

The current NFS client congestion logic is severly broken, it marks the
backing device congested during each nfs_writepages() call but doesn't
mirror this in nfs_writepage() which makes for deadlocks.  Also it
implements its own waitqueue.

Replace this by a more regular congestion implementation that puts a cap on
the number of active writeback pages and uses the bdi congestion waitqueue.

Also always use an interruptible wait since it makes sense to be able to
SIGKILL the process even for mounts without 'intr'.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Acked-by: Trond Myklebust <trond.myklebust@fys.uio.no>
Cc: Christoph Lameter <clameter@engr.sgi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 16 insertions, 0 deletions

diff --git a/mm/backing-dev.c b/mm/backing-dev.c
index f50a2811f9dc..e5de3781d3fe 100644
--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -55,6 +55,22 @@ long congestion_wait(int rw, long timeout)
 }
 EXPORT_SYMBOL(congestion_wait);
 
+long congestion_wait_interruptible(int rw, long timeout)
+{
+	long ret;
+	DEFINE_WAIT(wait);
+	wait_queue_head_t *wqh = &congestion_wqh[rw];
+
+	prepare_to_wait(wqh, &wait, TASK_INTERRUPTIBLE);
+	if (signal_pending(current))
+		ret = -ERESTARTSYS;
+	else
+		ret = io_schedule_timeout(timeout);
+	finish_wait(wqh, &wait);
+	return ret;
+}
+EXPORT_SYMBOL(congestion_wait_interruptible);
+
 /**
  * congestion_end - wake up sleepers on a congested backing_dev_info
  * @rw: READ or WRITE