Mark IO pipeline with PF_FSTRANS

In order to avoid deadlocking in the IO pipeline it is critical that
pageout be avoided during direct memory reclaim.  This ensures that
the pipeline threads can always make forward progress and never end
up blocking on a DMU transaction.  For this very reason Linux now
provides the PF_FSTRANS flag which may be set in the process context.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>

module/zfs/txg.c

@@ -483,15 +483,7 @@ txg_sync_thread(dsl_pool_t *dp)
 	vdev_stat_t *vs1, *vs2;
 	clock_t start, delta;
 
-#ifdef _KERNEL
-	/*
-	 * Annotate this process with a flag that indicates that it is
-	 * unsafe to use KM_SLEEP during memory allocations due to the
-	 * potential for a deadlock.  KM_PUSHPAGE should be used instead.
-	 */
-	current->flags |= PF_NOFS;
-#endif /* _KERNEL */
-
+	(void) spl_fstrans_mark();
 	txg_thread_enter(tx, &cpr);
 
 	vs1 = kmem_alloc(sizeof (vdev_stat_t), KM_PUSHPAGE);