From: Richard Yao <ryao@cs.stonybrook.edu>
Date: Mon, 16 Apr 2012 10:56:20 +0000 (-0400)
Subject: Disable direct reclaim on zvols
X-Git-Tag: zfs-0.6.0-rc9~20
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=ce90208cf9e04df966429f115d8831371ea9afce;p=zfs

Disable direct reclaim on zvols

Previously, it was possible for the direct reclaim path to be invoked
when a write to a zvol was made. When a zvol is used as a swap device,
this often causes swap requests to depend on additional swap requests,
which deadlocks. We address this by disabling the direct reclaim path
on zvols.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #342
---

diff --git a/module/zfs/zvol.c b/module/zfs/zvol.c
index 9b1313402..9dd9547e2 100644
--- a/module/zfs/zvol.c
+++ b/module/zfs/zvol.c
@@ -1390,8 +1390,14 @@ zvol_init(void)
 {
 	int error;
 
+	/*
+	 * The zvol taskqs are created with TASKQ_NORECLAIM so they may be
+	 * used safely as a swap device.  If direct reclaim is allowed then
+	 * they quickly deadlock in one of the internal memory allocations.
+	 */
 	zvol_taskq = taskq_create(ZVOL_DRIVER, zvol_threads, maxclsyspri,
-		                  zvol_threads, INT_MAX, TASKQ_PREPOPULATE);
+				  zvol_threads, INT_MAX,
+				  TASKQ_PREPOPULATE | TASKQ_NORECLAIM);
 	if (zvol_taskq == NULL) {
 		printk(KERN_INFO "ZFS: taskq_create() failed\n");
 		return (-ENOMEM);