pagecache: add switch to close the feature completely

euler inclusion
category: bugfix
CVE: NA
Bugzilla: 9580

---------------------------

The patch control the open/close of the feature by the
/proc/sys/vm/cache_reclaim_enable, hence we can completely
close all background thread for user demand.
Signed-off-by: Nzhongjiang <zhongjiang@huawei.com>
Reviewed-by: NJing Xiangfeng <jingxiangfeng@huawei.com>
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>

include/linux/swap.h

@@ -380,12 +380,15 @@ extern int vm_cache_reclaim_s_max;
 extern int vm_cache_reclaim_weight;
 extern int vm_cache_reclaim_weight_min;
 extern int vm_cache_reclaim_weight_max;
+extern int vm_cache_reclaim_enable;
 extern unsigned long page_cache_over_limit(void);
 extern unsigned long shrink_page_cache(gfp_t mask);
 extern int cache_limit_ratio_sysctl_handler(struct ctl_table *table, int write,
 			void __user *buffer, size_t *length, loff_t *ppos);
 extern int cache_limit_mbytes_sysctl_handler(struct ctl_table *table, int write,
 			void __user *buffer, size_t *length, loff_t *ppos);
+extern int cache_reclaim_enable_handler(struct ctl_table *table, int write,
+			void __user *buffer, size_t *length, loff_t *ppos);
 #endif
 
 #ifdef CONFIG_NUMA

kernel/sysctl.c

@@ -1383,6 +1383,15 @@ static struct ctl_table vm_table[] = {
 		.extra1         = &vm_cache_reclaim_weight_min,
 		.extra2         = &vm_cache_reclaim_weight_max,
 	},
+	{
+		.procname	= "cache_reclaim_enable",
+		.data		= &vm_cache_reclaim_enable,
+		.maxlen		= sizeof(vm_cache_reclaim_enable),
+		.mode		= 0644,
+		.proc_handler	= cache_reclaim_enable_handler,
+		.extra1		= &zero,
+		.extra2		= &one,
+	},
 #endif
 #ifdef CONFIG_HUGETLB_PAGE
 	{

mm/vmscan.c

@@ -179,6 +179,7 @@ int vm_cache_reclaim_s_max;
 int vm_cache_reclaim_weight __read_mostly;
 int vm_cache_reclaim_weight_min;
 int vm_cache_reclaim_weight_max;
+int vm_cache_reclaim_enable;
 static DEFINE_PER_CPU(struct delayed_work, vmscan_work);
 #endif
 
@@ -3942,14 +3943,22 @@ static void shrink_shepherd(struct work_struct *w)
 	for_each_online_cpu(cpu) {
 		struct delayed_work *work = &per_cpu(vmscan_work, cpu);
 
-		if (!delayed_work_pending(work))
+		if (!delayed_work_pending(work) && vm_cache_reclaim_enable)
 			queue_delayed_work_on(cpu, system_wq, work, 0);
 	}
 
 	put_online_cpus();
 
-	schedule_delayed_work(&shepherd,
-		round_jiffies_relative((unsigned long)vm_cache_reclaim_s * HZ));
+	/* we want all kernel thread to stop */
+	if (vm_cache_reclaim_enable) {
+		if (vm_cache_reclaim_s == 0)
+			schedule_delayed_work(&shepherd,
+				round_jiffies_relative(120 * HZ));
+		else
+			schedule_delayed_work(&shepherd,
+				round_jiffies_relative((unsigned long)
+				vm_cache_reclaim_s * HZ));
+	}
 }
 
 static void shrink_shepherd_timer(void)
@@ -3981,15 +3990,16 @@ static void shrink_page_cache_work(struct work_struct *w)
 	struct delayed_work *work = to_delayed_work(w);
 	unsigned long nr_pages;
 
-	if (vm_cache_reclaim_s == 0) {
-		queue_delayed_work_on(smp_processor_id(), system_wq,
-					work, round_jiffies_relative(120 * HZ));
+	/*
+	 * if vm_cache_reclaim_enable or vm_cache_reclaim_s is zero,
+	 * we do not shrink page cache again.
+	 */
+	if (vm_cache_reclaim_s == 0 || !vm_cache_reclaim_enable)
 		return;
-	}
 
 	/* It should wait more time if we hardly reclaim the page cache */
 	nr_pages = shrink_page_cache(GFP_KERNEL);
-	if (nr_pages < SWAP_CLUSTER_MAX)
+	if ((nr_pages < SWAP_CLUSTER_MAX) && vm_cache_reclaim_enable)
 		queue_delayed_work_on(smp_processor_id(), system_wq, work,
 			round_jiffies_relative(120 * HZ));
 }
@@ -4008,6 +4018,7 @@ static void shrink_page_cache_init(void)
 	vm_cache_reclaim_weight = 1;
 	vm_cache_reclaim_weight_min = 1;
 	vm_cache_reclaim_weight_max = 100;
+	vm_cache_reclaim_enable = 1;
 
 	shrink_shepherd_timer();
 }
@@ -4018,6 +4029,22 @@ static int kswapd_cpu_down_prep(unsigned int cpu)
 
 	return 0;
 }
+
+int cache_reclaim_enable_handler(struct ctl_table *table, int write,
+			void __user *buffer, size_t *length, loff_t *ppos)
+{
+	int ret;
+
+	ret = proc_dointvec_minmax(table, write, buffer, length, ppos);
+	if (ret)
+		return ret;
+
+	if (write)
+		schedule_delayed_work(&shepherd, round_jiffies_relative(
+			(unsigned long)vm_cache_reclaim_s * HZ));
+
+	return 0;
+}
 #endif
 
 /* It's optimal to keep kswapds on the same CPUs as their memory, but