mm/vmscan: setup drop_caches_loop_limit in cmdline

hulk inclusion
category: bugfix
bugzilla: 175105
CVE: NA

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

When !CONFIG_SYSCTL, drop_caches_loop_limit is invisible.
Add cmdline "drop_caches_loop_limit=" to set it.
This parameter can limit the number of loops per node.

Fixes: ceb5620e ("mm/vmscan: add drop_caches_loop_limit to break loop in drop_slab_node")
Signed-off-by: NLiu Shixin <liushixin2@huawei.com>
Reviewed-by: NKefeng Wang <wangkefeng.wang@huawei.com>
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>

fs/drop_caches.c

@@ -13,7 +13,6 @@
 
 /* A global variable is a bit ugly, but it keeps the code simple */
 int sysctl_drop_caches;
-unsigned int sysctl_drop_caches_loop_limit __read_mostly;
 
 static void drop_pagecache_sb(struct super_block *sb, void *unused)
 {

include/linux/mm.h

@@ -2769,7 +2769,7 @@ extern bool process_shares_mm(struct task_struct *p, struct mm_struct *mm);
 
 #ifdef CONFIG_SYSCTL
 extern int sysctl_drop_caches;
-extern unsigned int sysctl_drop_caches_loop_limit;
+extern unsigned int drop_caches_loop_limit;
 int drop_caches_sysctl_handler(struct ctl_table *, int,
 					void __user *, size_t *, loff_t *);
 #endif

kernel/sysctl.c

@@ -1479,7 +1479,7 @@ static struct ctl_table vm_table[] = {
 	},
 	{
 		.procname	= "drop_caches_loop_limit",
-		.data		= &sysctl_drop_caches_loop_limit,
+		.data		= &drop_caches_loop_limit,
 		.maxlen		= sizeof(unsigned int),
 		.mode		= 0644,
 		.proc_handler	= proc_douintvec,

mm/vmscan.c

@@ -723,12 +723,21 @@ static unsigned long shrink_slab(gfp_t gfp_mask, int nid,
 	return freed;
 }
 
+unsigned int drop_caches_loop_limit __read_mostly;
+static int __init drop_caches_loop_limit_setup(char *s)
+{
+	int ret = kstrtouint(s, 10, &drop_caches_loop_limit);
+
+	if (ret)
+		pr_info("Parse drop_caches_loop_limit failed: ret: %d\n", ret);
+	return 1;
+}
+__setup("drop_caches_loop_limit=", drop_caches_loop_limit_setup);
+
 void drop_slab_node(int nid)
 {
 	unsigned long freed;
-#ifdef CONFIG_SYSCTL
 	unsigned int counts = 0;
-#endif
 
 	do {
 		struct mem_cgroup *memcg = NULL;
@@ -742,17 +751,15 @@ void drop_slab_node(int nid)
 			freed += shrink_slab(GFP_KERNEL, nid, memcg, 0);
 		} while ((memcg = mem_cgroup_iter(NULL, memcg, NULL)) != NULL);
 
-#ifdef CONFIG_SYSCTL
-		if (unlikely(sysctl_drop_caches_loop_limit)) {
+		if (unlikely(drop_caches_loop_limit)) {
 			counts++;
-			if (counts >= sysctl_drop_caches_loop_limit) {
+			if (counts >= drop_caches_loop_limit) {
 				pr_info("%s (%d): drop_caches early break: %u loops\n",
 					current->comm, task_pid_nr(current),
 					counts);
 				return;
 			}
 		}
-#endif
 	} while (freed > 10);
 }