[PATCH 05/07]

This patche makes the memory hotplug chain's mutex held for a shorter time:
when memory is offlined or onlined a work item is added to the global
workqueue.
When the work item is run, it notifies the ipcns notifier chain with the
IPCNS_MEMCHANGED event.

Signed-off-by: Nadia Derbey <Nadia.Derbey@bull.net>

---
 ipc/util.c |   17 +++++++++++++++--
 1 file changed, 15 insertions(+), 2 deletions(-)

Index: linux-2.6.24/ipc/util.c
===================================================================
--- linux-2.6.24.orig/ipc/util.c	2008-01-31 11:04:51.000000000 +0100
+++ linux-2.6.24/ipc/util.c	2008-01-31 11:41:01.000000000 +0100
@@ -57,6 +57,14 @@ atomic_t nr_ipc_ns = ATOMIC_INIT(1);
 
 #ifdef CONFIG_MEMORY_HOTPLUG
 
+static void ipc_memory_notifier(struct work_struct *work)
+{
+	ipcns_notify(IPCNS_MEMCHANGED);
+}
+
+static DECLARE_WORK(ipc_memory_wq, ipc_memory_notifier);
+
+
 static int ipc_memory_callback(struct notifier_block *self,
 				unsigned long action, void *arg)
 {
@@ -65,9 +73,14 @@ static int ipc_memory_callback(struct no
 	case MEM_OFFLINE:   /* or offline: it's time to recompute msgmni */
 		/*
 		 * This is done by invoking the ipcns notifier chain with the
-		 * IPC_MEMCHANGED event
+		 * IPC_MEMCHANGED event.
+		 * In order not to keep the lock on the hotplug memory chain
+		 * for too long, queue a work item that will, when waken up,
+		 * activate the ipcns notification chain.
+		 * No need to keep several ipc work items on the queue.
 		 */
-		ipcns_notify(IPCNS_MEMCHANGED);
+		if (!work_pending(&ipc_memory_wq))
+			schedule_work(&ipc_memory_wq);
 		break;
 	case MEM_GOING_ONLINE:
 	case MEM_GOING_OFFLINE:

--
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