mm: limit growth of 3% hardcoded other user reserve

index 3393114..3956d3d 100644
@@ -1677,6 +1677,8 @@ int in_gate_area_no_mm(unsigned long addr);
 
 int drop_caches_sysctl_handler(struct ctl_table *, int,
 					void __user *, size_t *, loff_t *);
+int reserve_pages_sysctl_handler(struct ctl_table *, int,
+					void __user *, size_t *, loff_t *);
 unsigned long shrink_slab(struct shrink_control *shrink,
 			  unsigned long nr_pages_scanned,
 			  unsigned long lru_pages);

index afc1dc6..dbb7b93 100644
@@ -97,6 +97,7 @@
 /* External variables not in a header file. */
 extern int sysctl_overcommit_memory;
 extern int sysctl_overcommit_ratio;
+extern unsigned long sysctl_user_reserve_pages;
 extern int max_threads;
 extern int suid_dumpable;
 #ifdef CONFIG_COREDUMP

@@ -1430,6 +1431,13 @@ static struct ctl_table vm_table[] = {
 		.extra2		= &one,
 	},
 #endif
+	{
+		.procname	= "user_reserve_pages",
+		.data		= &sysctl_user_reserve_pages,
+		.maxlen		= sizeof(sysctl_user_reserve_pages),
+		.mode		= 0644,
+		.proc_handler	= proc_doulongvec_minmax,
+	},
 	{ }
 };
 

index 49dc7d5..aeaf83f 100644
@@ -33,6 +33,7 @@
 #include <linux/uprobes.h>
 #include <linux/rbtree_augmented.h>
 #include <linux/sched/sysctl.h>
+#include <linux/sysctl.h>
 
 #include <asm/uaccess.h>
 #include <asm/cacheflush.h>

@@ -84,6 +85,7 @@ EXPORT_SYMBOL(vm_get_page_prot);
 int sysctl_overcommit_memory __read_mostly = OVERCOMMIT_GUESS;  /* heuristic overcommit */
 int sysctl_overcommit_ratio __read_mostly = 50;	/* default is 50% */
 int sysctl_max_map_count __read_mostly = DEFAULT_MAX_MAP_COUNT;
+unsigned long sysctl_user_reserve_pages __read_mostly = 1UL << (27 - PAGE_SHIFT); /* 128MB */
 /*
  * Make sure vm_committed_as in one cacheline and not cacheline shared with
  * other variables. It can be updated by several CPUs frequently.

@@ -183,10 +185,11 @@ int __vm_enough_memory(struct mm_struct *mm, long pages, int cap_sys_admin)
 		allowed -= allowed / 32;
 	allowed += total_swap_pages;
 
-	/* Don't let a single process grow too big:
-	   leave 3% of the size of this process for other processes */
+	/*
+ 	 * Don't let a single process grow so big a user can't recover
+         */
 	if (mm)
-		allowed -= mm->total_vm / 32;
+		allowed -= min(mm->total_vm / 32, sysctl_user_reserve_pages);
 
 	if (percpu_counter_read_positive(&vm_committed_as) < allowed)
 		return 0;

@@ -3067,3 +3070,23 @@ void __init mmap_init(void)
 	ret = percpu_counter_init(&vm_committed_as, 0);
 	VM_BUG_ON(ret);
 }
+
+/*
+ * Initialise sysctl_user_reserve_pages.
+ *
+ * The purpose of sysctl_user_reserve_pages is to prevent a single 
+ * process from allocating all free memory in OVERCOMMIT_NEVER mode.
+ *
+ * The default value is min(3% of free memory, 128MB) 
+ * 128MB is enough to recover with sshd/login, bash, and top/kill.
+ */
+int __meminit init_user_reserve(void)
+{
+	unsigned long free;
+
+	free = global_page_state(NR_FREE_PAGES);
+
+	sysctl_user_reserve_pages = min(free / 32, 1UL << (27 - PAGE_SHIFT));
+	return 0;
+}
+module_init(init_user_reserve)

index f5d57a3..0137ab2 100644
@@ -30,6 +30,7 @@
 #include <linux/syscalls.h>
 #include <linux/audit.h>
 #include <linux/sched/sysctl.h>
+#include <linux/sysctl.h>
 
 #include <asm/uaccess.h>
 #include <asm/tlb.h>

@@ -63,6 +64,7 @@ int sysctl_overcommit_memory = OVERCOMMIT_GUESS; /* heuristic overcommit */
 int sysctl_overcommit_ratio = 50; /* default is 50% */
 int sysctl_max_map_count = DEFAULT_MAX_MAP_COUNT;
 int sysctl_nr_trim_pages = CONFIG_NOMMU_INITIAL_TRIM_EXCESS;
+unsigned long sysctl_user_reserve_pages __read_mostly = 1UL << (27 - PAGE_SHIFT); /* 128MB */
 int heap_stack_gap = 0;
 
 atomic_long_t mmap_pages_allocated;

@@ -1945,9 +1947,11 @@ int __vm_enough_memory(struct mm_struct *mm, long pages, int cap_sys_admin)
 	allowed += total_swap_pages;
 
 	/* Don't let a single process grow too big:
-	   leave 3% of the size of this process for other processes */
+	 * leave the smaller of 3% of the size of this process 
+         * or 8MB for other processes
+         */
 	if (mm)
-		allowed -= mm->total_vm / 32;
+		allowed -= min(mm->total_vm / 32, sysctl_user_reserve_pages);
 
 	if (percpu_counter_read_positive(&vm_committed_as) < allowed)
 		return 0;

@@ -2109,3 +2113,23 @@ int nommu_shrink_inode_mappings(struct inode *inode, size_t size,
 	up_write(&nommu_region_sem);
 	return 0;
 }
+
+/*
+ * Initialise sysctl_user_reserve_pages.
+ *
+ * The purpose of sysctl_user_reserve_pages is to prevent a single 
+ * process from allocating all free memory in OVERCOMMIT_NEVER mode.
+ *
+ * The default value is min(3% of free memory, 128MB) 
+ * 128MB is enough to recover with sshd/login, bash, and top/kill.
+ */
+int __meminit init_user_reserve(void)
+{
+	unsigned long free;
+
+	free = global_page_state(NR_FREE_PAGES);
+
+	sysctl_user_reserve_pages = min(free / 32, 1UL << (27 - PAGE_SHIFT));
+	return 0;
+}
+module_init(init_user_reserve)