pagecache: use the correct cache_reclaim_s immediately

euler inclusion
category: bugfix
CVE: NA
Bugzilla: 13084

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

when we set a large number in cache_reclaim_s to background thread
to reclaim free pagecache, And then set a minimum number to it.

It will trigger an unexpected result. we must drain the time slice
of cache_reclaim_s. hence we will wait too long time for that.
Signed-off-by: Nzhong jiang <zhongjiang@huawei.com>
Reviewed-by: NJing Xiangfeng <jingxiangfeng@huawei.com>
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>

include/linux/swap.h

@@ -389,6 +389,8 @@ 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);
+extern int cache_reclaim_sysctl_handler(struct ctl_table *table, int write,
+			void __user *buffer, size_t *length, loff_t *ppos);
 #endif
 
 #ifdef CONFIG_NUMA

kernel/sysctl.c

@@ -1382,7 +1382,7 @@ static struct ctl_table vm_table[] = {
 		.data           = &vm_cache_reclaim_s,
 		.maxlen         = sizeof(vm_cache_reclaim_s),
 		.mode           = 0644,
-		.proc_handler   = proc_dointvec_minmax,
+		.proc_handler   = cache_reclaim_sysctl_handler,
 		.extra1         = &vm_cache_reclaim_s_min,
 		.extra2         = &vm_cache_reclaim_s_max,
 	},

mm/vmscan.c

@@ -4045,6 +4045,23 @@ int cache_reclaim_enable_handler(struct ctl_table *table, int write,
 
 	return 0;
 }
+
+int cache_reclaim_sysctl_handler(struct ctl_table *table, int write,
+			void __user *buffer, size_t *length, loff_t *ppos)
+{
+	int ret, cpu;
+
+	ret = proc_dointvec_minmax(table, write, buffer, length, ppos);
+	if (ret)
+		return ret;
+
+	if (write)
+		mod_delayed_work_on(cpu, system_wq, &shepherd,
+				round_jiffies_relative(
+				(unsigned long)vm_cache_reclaim_s * HZ));
+
+	return ret;
+}
 #endif
 
 /* It's optimal to keep kswapds on the same CPUs as their memory, but