xfs: mark the xfssyncd workqueue as non-reentrant

On a system with lots of memory pressure that is stuck on synchronous inode
reclaim the workqueue code will run one instance of the inode reclaim work
item on every CPU. which is not what we want.  Make sure to mark the
xfssyncd workqueue as non-reentrant to make sure there only is one instace
of each running globally.  Also stop using special paramater for the
workqueue; now that we guarantee each fs has only running one of each works
at a time there is no need to artificially lower max_active and compensate
for that by setting the WQ_CPU_INTENSIVE flag.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Ben Myers <bpm@sgi.com>

fs/xfs/xfs_super.c

@@ -1625,12 +1625,12 @@ STATIC int __init
 xfs_init_workqueues(void)
 {
 	/*
-	 * max_active is set to 8 to give enough concurency to allow
-	 * multiple work operations on each CPU to run. This allows multiple
-	 * filesystems to be running sync work concurrently, and scales with
-	 * the number of CPUs in the system.
+	 * We never want to the same work item to run twice, reclaiming inodes
+	 * or idling the log is not going to get any faster by multiple CPUs
+	 * competing for ressources.  Use the default large max_active value
+	 * so that even lots of filesystems can perform these task in parallel.
 	 */
-	xfs_syncd_wq = alloc_workqueue("xfssyncd", WQ_CPU_INTENSIVE, 8);
+	xfs_syncd_wq = alloc_workqueue("xfssyncd", WQ_NON_REENTRANT, 0);
 	if (!xfs_syncd_wq)
 		return -ENOMEM;
 	return 0;