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Subject[PATCH] Improve cache_reap hotplug cpu support
I found that there was room for improvement in the hotplug cpu code
in cache_reap. This applies to the code that moved cache_reap out
of timer context.

The patch applies over 2.6.8.1-mm2.

Signed-off-by: Dimitri Sivanich <sivanich@sgi.com>


Index: linux/mm/slab.c
===================================================================
--- linux.orig/mm/slab.c 2004-08-19 14:34:03.000000000 -0500
+++ linux/mm/slab.c 2004-08-19 15:19:34.000000000 -0500
@@ -613,12 +613,22 @@ static void __devinit start_cpu_timer(in
* init_workqueues() has already run, so keventd will be setup
* at that time.
*/
- if (keventd_up() && reap_work->func == NULL) {
- INIT_WORK(reap_work, cache_reap, NULL);
+ if (keventd_up() && reap_work->data == NULL) {
+ INIT_WORK(reap_work, cache_reap, reap_work);
schedule_delayed_work_on(cpu, reap_work, HZ + 3 * cpu);
}
}

+#ifdef CONFIG_HOTPLUG_CPU
+static void stop_cpu_timer(int cpu)
+{
+ struct work_struct *reap_work = &per_cpu(reap_work, cpu);
+
+ /* Null out this otherwise unused pointer for checking in cache_reap */
+ reap_work->data = NULL;
+}
+#endif
+
static struct array_cache *alloc_arraycache(int cpu, int entries, int batchcount)
{
int memsize = sizeof(void*)*entries+sizeof(struct array_cache);
@@ -670,6 +680,7 @@ static int __devinit cpuup_callback(stru
break;
#ifdef CONFIG_HOTPLUG_CPU
case CPU_DEAD:
+ stop_cpu_timer(cpu);
/* fall thru */
case CPU_UP_CANCELED:
down(&cache_chain_sem);
@@ -2731,10 +2742,19 @@ static void drain_array_locked(kmem_cach
* If we cannot acquire the cache chain semaphore then just give up - we'll
* try again on the next iteration.
*/
-static void cache_reap(void *unused)
+static void cache_reap(void *work)
{
struct list_head *walk;

+#ifdef CONFIG_HOTPLUG_CPU
+ if (unlikely((work==NULL) ||
+ ((struct work_struct *)work)->data == NULL)) {
+ /* We've been moved off the original cpu due to HOTPLUG,
+ * don't resched.
+ */
+ return;
+ }
+#endif
if (down_trylock(&cache_chain_sem)) {
/* Give up. Setup the next iteration. */
schedule_delayed_work(&__get_cpu_var(reap_work), REAPTIMEOUT_CPUC + smp_processor_id());
-
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