linux-kernel - [PATCH 3/3] zram: adjust the number of zram thread

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Date:   Thu, 22 Sep 2016 15:42:45 +0900
From:   Minchan Kim <minchan@...nel.org>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        linux-kernel@...r.kernel.org, Minchan Kim <minchan@...nel.org>
Subject: [PATCH 3/3] zram: adjust the number of zram thread

It's pointless to keep many workers greater than the number of
online CPU so adjust the number of worker whenever changing
online CPU number.

Signed-off-by: Minchan Kim <minchan@...nel.org>
---
 drivers/block/zram/zram_drv.c | 94 ++++++++++++++++++++++++++++++++-----------
 1 file changed, 71 insertions(+), 23 deletions(-)

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index abab76e2cf28..a930f96f01ab 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -31,6 +31,7 @@
 #include <linux/err.h>
 #include <linux/idr.h>
 #include <linux/sysfs.h>
+#include <linux/cpu.h>
 
 #include "zram_drv.h"
 
@@ -987,6 +988,8 @@ struct zram_workers {
 	struct list_head worker_list;
 	wait_queue_head_t req_wait;
 	spinlock_t req_lock;
+
+	struct notifier_block notifier;
 } workers;
 
 struct bio_request {
@@ -1269,52 +1272,97 @@ static int zram_thread(void *data)
 	return 0;
 }
 
-static void destroy_workers(void)
+static int __zram_cpu_notifier(void *dummy, unsigned long action,
+				unsigned long cpu)
 {
 	struct zram_worker *worker;
 
-	while (!list_empty(&workers.worker_list)) {
+	switch (action) {
+	case CPU_UP_PREPARE:
+		worker = kmalloc(sizeof(*worker), GFP_KERNEL);
+		if (!worker) {
+			pr_err("Can't allocate a worker\n");
+			return NOTIFY_BAD;
+		}
+
+		worker->task = kthread_run(zram_thread, NULL, "zramd-%lu", cpu);
+		if (IS_ERR(worker->task)) {
+			kfree(worker);
+			pr_err("Can't allocate a zram thread\n");
+			return NOTIFY_BAD;
+		}
+
+		spin_lock(&workers.req_lock);
+		list_add(&worker->list, &workers.worker_list);
+		spin_unlock(&workers.req_lock);
+		break;
+	case CPU_DEAD:
+	case CPU_UP_CANCELED:
+		spin_lock(&workers.req_lock);
+		WARN_ON(list_empty(&workers.worker_list));
+
 		worker = list_first_entry(&workers.worker_list,
-				struct zram_worker,
-				list);
-		kthread_stop(worker->task);
+					struct zram_worker, list);
 		list_del(&worker->list);
+		spin_unlock(&workers.req_lock);
+
+		kthread_stop(worker->task);
 		kfree(worker);
+		break;
+	default:
+		break;
 	}
+	return NOTIFY_OK;
+}
+
+static int zram_cpu_notifier(struct notifier_block *nb,
+		unsigned long action, void *pcpu)
+{
+	unsigned long cpu = (unsigned long)pcpu;
+
+	return __zram_cpu_notifier(NULL, action, cpu);
+}
+
+static void destroy_workers(void)
+{
+	unsigned long cpu;
+
+	cpu_notifier_register_begin();
+	for_each_online_cpu(cpu)
+		__zram_cpu_notifier(NULL, CPU_UP_CANCELED, cpu);
+	__unregister_cpu_notifier(&workers.notifier);
+	cpu_notifier_register_done();
 
 	WARN_ON(workers.nr_running);
 }
 
 static int create_workers(void)
 {
-	int i;
-	int nr_cpu = num_online_cpus();
-	struct zram_worker *worker;
+	int cpu;
 
 	INIT_LIST_HEAD(&workers.worker_list);
 	INIT_LIST_HEAD(&workers.req_list);
 	spin_lock_init(&workers.req_lock);
 	init_waitqueue_head(&workers.req_wait);
 
-	for (i = 0; i < nr_cpu; i++) {
-		worker = kmalloc(sizeof(*worker), GFP_KERNEL);
-		if (!worker)
-			goto error;
-
-		worker->task = kthread_run(zram_thread, NULL, "zramd-%d", i);
-		if (IS_ERR(worker->task)) {
-			kfree(worker);
-			goto error;
-		}
-
-		list_add(&worker->list, &workers.worker_list);
+	workers.notifier.notifier_call = zram_cpu_notifier;
+	cpu_notifier_register_begin();
+	for_each_online_cpu(cpu) {
+		if (__zram_cpu_notifier(NULL, CPU_UP_PREPARE, cpu) ==
+				NOTIFY_BAD)
+			goto cleanup;
 	}
 
+	__register_cpu_notifier(&workers.notifier);
+	cpu_notifier_register_done();
+
 	return 0;
+cleanup:
+	for_each_online_cpu(cpu)
+		__zram_cpu_notifier(NULL, CPU_UP_CANCELED, cpu);
+	cpu_notifier_register_done();
 
-error:
-	destroy_workers();
-	return 1;
+	return -ENOMEM;
 }
 
 static int zram_rw_async_page(struct zram *zram,
-- 
2.7.4