MemoryMonitor: use /proc/*/oom_score_adj rather than /proc/*/oom_adj

On newer kernels /proc/*/oom_adj is deprecated and should not be used anymore. As Open
webOS requires at least a linux 3.3 kernel this changes the use to the new
/proc/*/oom_score_adj entry but still keeps backward compatiblity for older kernels which
onles provides /proc/*/oom_adj.

More information about the change are available on the following pages:
- torvalds/linux@a63d83f#include/linux/oom.h
- https://www.redhat.com/archives/lvm-devel/2011-July/msg00097.html

Open-webOS-DCO-1.0-Signed-off-by: Simon Busch <morphis@gravedo.de>

Src/base/MemoryMonitor.cpp

@@ -22,6 +22,7 @@
 #include "Common.h"
 
 #include <sys/types.h>
+#include <sys/stat.h>
 #include <unistd.h>
 #include <fstream>
 #include <strings.h>
@@ -51,6 +52,12 @@ static const std::string sMBLabel("mb");
 static const std::string sProcRSS("VmRSS");
 static const std::string sProcSwap("VmSwap");
 
+#define OOM_ADJ_PATH			"/proc/%d/oom_adj"
+#define OOM_SCORE_ADJ_PATH		"/proc/%d/oom_score_adj"
+
+#define OOM_ADJ_VALUE			-17
+#define OOM_SCORE_ADJ_VALUE		-1000
+
 MemoryMonitor* MemoryMonitor::instance()
 {
 	static MemoryMonitor* s_instance = 0;
@@ -68,19 +75,41 @@ MemoryMonitor::MemoryMonitor()
 	m_fileName[kFileNameLen - 1] = 0;
 	snprintf(m_fileName, kFileNameLen - 1, "/proc/%d/statm", getpid());
 
-	char oom_adj[kFileNameLen];
-	snprintf(oom_adj, kFileNameLen - 1, "/proc/%d/oom_adj", getpid());
-	FILE* f = fopen(oom_adj, "wb");
-	if (f) {
-		size_t result = fwrite("-17\n", 4, 1, f);
-		(void)result;
-
-		fclose(f);	
-	}
+	/* Adjust OOM killer so we're never killed for memory reasons */
+	adjustOomScore();
 }
 
 MemoryMonitor::~MemoryMonitor()
-{    
+{
+}
+
+void MemoryMonitor::adjustOomScore()
+{
+	struct stat st;
+	int score_value = 0;
+
+	/* Adjust OOM killer so we're never killed for memory reasons */
+	char oom_adj_path[kFileNameLen];
+	snprintf(oom_adj_path, kFileNameLen - 1, OOM_SCORE_ADJ_PATH, getpid());
+	if (stat(oom_adj_path, &st) == -1) {
+		snprintf(oom_adj_path, kFileNameLen - 1, OOM_ADJ_PATH, getpid());
+		if (stat(oom_adj_path, &st) == -1) {
+			g_warning("Failed to adjust OOM value");
+			return;
+		}
+		else {
+			score_value = OOM_ADJ_VALUE;
+		}
+	}
+	else {
+		score_value = OOM_SCORE_ADJ_VALUE;
+	}
+
+	FILE* f = fopen(oom_adj_path, "wb");
+	if (f) {
+		fprintf(f, "%i\n", score_value);
+		fclose(f);
+	}
 }
 
 void MemoryMonitor::start()

Src/base/MemoryMonitor.h

@@ -75,7 +75,9 @@ class MemoryMonitor : public QObject
 	int getCurrentRssUsage() const;
 
 	int getProcessMemInfo(pid_t pid);
-
+
+	void adjustOomScore();
+
 #if defined(HAS_MEMCHUTE)
     static void memchuteCallback(MemchuteThreshold threshold);
 	void memchuteStateChanged();