membomb: add membomb.mmap

Created for #320
but does not actually repro the issue.

Author: rfjakob

contrib/membomb/.gitignore

@@ -1,2 +1,3 @@
 /membomb
 /membomb.subthread
+/membomb.mmap

contrib/membomb/Makefile

@@ -1,18 +1,21 @@
 CFLAGS += -Wall -Wextra -g -fstack-protector-all -std=gnu99
 
 .PHONY: all
-all: membomb membomb.subthread
+all: membomb membomb.subthread membomb.mmap
 
 membomb : $(wildcard *.c *.h) Makefile
 	$(CC) $(CFLAGS) -o $@ eat_all_memory.c membomb.c
 
 membomb.subthread: $(wildcard *.c *.h) Makefile
 	$(CC) $(CFLAGS) -lpthread -o $@ eat_all_memory.c membomb.subthread.c
 
+membomb.mmap: $(wildcard *.c *.h) Makefile
+	$(CC) $(CFLAGS) -lpthread -o $@ eat_all_memory.c membomb.mmap.c
+
 .PHONY: format
 format:
 	clang-format --style=file -i *.c
 
 .PHONY: clean
 clean:
-	rm -f membomb membomb.subthread
+	rm -f membomb membomb.subthread membomb.mmap

contrib/membomb/eat_all_memory.c

@@ -5,14 +5,16 @@
 #include <sys/time.h>
 #include <unistd.h>
 
+#include "eat_all_memory.h"
+
 #define NUM_PAGES 10
 
 static void handle_sigterm(int sig)
 {
     printf("blocking SIGTERM %d\n", sig);
 }
 
-void eat_all_memory()
+void eat_all_memory(eat_how_enum eat_how)
 {
     long page_size = sysconf(_SC_PAGESIZE);
     long bs = page_size * NUM_PAGES;
@@ -21,10 +23,25 @@ void eat_all_memory()
     signal(SIGTERM, handle_sigterm);
     gettimeofday(&tv1, NULL);
     while (1) {
-        char* p = malloc(bs);
-        if (!p) {
-            printf("malloc failed\n");
-            continue;
+        char* p = NULL;
+        switch (eat_how) {
+        case EAT_MALLOC:
+            p = malloc(bs);
+            if (!p) {
+                perror("malloc failed");
+                continue;
+            }
+            break;
+        case EAT_MMAP_ANON:
+            p = mmap(NULL, bs, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+            if (p == MAP_FAILED) {
+                perror("mmap failed");
+                continue;
+            }
+            break;
+        default:
+            fprintf(stderr, "BUG: unknown eat_how=%d\n", eat_how);
+            exit(1);
         }
         for (int i = 0; i < NUM_PAGES; i++) {
             // Write to each page so the kernel really has to allocate it.

contrib/membomb/eat_all_memory.h

@@ -1 +1,6 @@
-void eat_all_memory();
+typedef enum {
+    EAT_MALLOC,
+    EAT_MMAP_ANON,
+} eat_how_enum;
+
+void eat_all_memory(eat_how_enum eat_how);

contrib/membomb/membomb.c

@@ -7,9 +7,12 @@
  * This file is part of the earlyoom project: https://github.com/rfjakob/earlyoom
  */
 
+#include <stdio.h>
+
 #include "eat_all_memory.h"
 
 int main()
 {
-    eat_all_memory();
+    printf("Using malloc\n");
+    eat_all_memory(EAT_MALLOC);
 }

contrib/membomb/membomb.mmap.c

@@ -0,0 +1,18 @@
+// SPDX-License-Identifier: MIT
+
+/* Use up all memory that we can get, as fast as we can.
+ * As progress information, prints how much memory we already
+ * have.
+ *
+ * This file is part of the earlyoom project: https://github.com/rfjakob/earlyoom
+ */
+
+#include <stdio.h>
+
+#include "eat_all_memory.h"
+
+int main()
+{
+    printf("Using mmap MAP_ANONYMOUS\n");
+    eat_all_memory(EAT_MMAP_ANON);
+}

contrib/membomb/membomb.subthread.c

@@ -17,7 +17,7 @@
 void* eat_all_memory_thread(__attribute__((__unused__)) void* arg)
 {
     printf("sub  thread = pid %d\n", gettid());
-    eat_all_memory();
+    eat_all_memory(EAT_MALLOC);
     return NULL;
 }