mmap: allow unlimited overcommit

Change-Id: Iba07b5c504b4a202cd163ce682f3fc72a31284a0

NEWS.md

@@ -535,3 +535,6 @@ Restrictions on McKernel
 
 25. The behaviors of madvise and mbind are changed to do nothing and
     report success as a workaround for Fugaku.
+
+26. mmap() allows unlimited overcommit. Note that it corresponds to
+    setting sysctl ``vm.overcommit_memory`` to 1.

kernel/include/mman.h

@@ -72,4 +72,11 @@
 #define	MS_INVALIDATE	0x02
 #define	MS_SYNC		0x04
 
+/* include/uapi/linux/mman.h */
+#define OVERCOMMIT_GUESS		0
+#define OVERCOMMIT_ALWAYS		1
+#define OVERCOMMIT_NEVER		2
+
+extern int sysctl_overcommit_memory;
+
 #endif /* HEADER_MMAN_H */

kernel/include/rusage_private.h

@@ -11,6 +11,7 @@
 #include <ihk/ihk_monitor.h>
 #include <ihk/debug.h>
 #include <memory.h>
+#include <mman.h>
 
 #ifdef ENABLE_RUSAGE
 
@@ -311,6 +312,9 @@ rusage_check_overmap(size_t len, int pgshift)
 {
 	int npages = 0, remain_pages = 0;
 
+	if (sysctl_overcommit_memory == OVERCOMMIT_ALWAYS)
+		return 0;
+
 	npages = (len + (1UL << pgshift) - 1) >> pgshift;
 	remain_pages = (rusage.total_memory - rusage.total_memory_usage)
 			>> pgshift;

kernel/mem.c

@@ -62,6 +62,7 @@ extern int interrupt_from_user(void *);
 struct tlb_flush_entry tlb_flush_vector[IHK_TLB_FLUSH_IRQ_VECTOR_SIZE];
 
 int anon_on_demand = 0;
+int sysctl_overcommit_memory = OVERCOMMIT_ALWAYS;
 
 static struct ihk_mc_pa_ops *pa_ops;