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

This change is based on a change made originally to luna-sysmgr by Simon
Busch, at

openwebos/luna-sysmgr@fdf37758e36da98268da95051cb6

On newer kernels /proc/*/oom_adj is deprecated and should not be used anymor
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 that provide /proc/*/oom_adj.

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

Open webOS DCO 1.0 Signed off by Simon Busch [morphis@gravedo.de]
Open-webOS-DCO-1.0-Signed-off-by: Eric Blade <eric.blade@palm.com>

Change-Id: I8fd3d4acd2ce71338391bad0e231fce1869160e6

Src/webbase/MemoryWatcher.cpp

@@ -22,6 +22,7 @@
 #include "Common.h"
 
 #include <sys/types.h>
+#include <sys/stat.h>
 #include <unistd.h>
 #include <fstream>
 #include <strings.h>
@@ -33,6 +34,12 @@
 #include "Time.h"
 #include "WebAppManager.h"
 
+#define OOM_ADJ_PATH "/proc/self/oom_adj"
+#define OOM_SCORE_ADJ_PATH "/proc/self/oom_score_adj"
+
+#define OOM_ADJ_VALUE -17
+#define OOM_SCORE_ADJ_VALUE -1000
+
 static const int kTimerMs = 5000;
 static const int kLowMemExpensiveTimeoutMultiplier = 2;
 static const uint32_t kMinIntervalBetweenLowMemActions = 30000;
@@ -57,15 +64,6 @@ MemoryWatcher::MemoryWatcher()
 	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);
-		Q_UNUSED(result);
-		fclose(f);	
-	}
-
 	m_timeAtLastLowMemAction = 0;
 	m_timeAtLastExpensiveLowMemAction = 0;
 }
@@ -90,6 +88,7 @@ void MemoryWatcher::start()
 		g_warning("Failed to create MemchuteWatcher");
 	}
 #endif	    
+    adjustOomScore();
 }
 
 static const char* nameForState(MemoryWatcher::MemState state)
@@ -195,6 +194,37 @@ void MemoryWatcher::doLowMemActions(bool allowExpensive)
     g_warning("MemoryWatcher: RSS usage after low memory actions: %dMB\n", m_currRssUsage);
 }
 
+void MemoryWatcher::adjustOomScore() 
+{
+    struct stat st;
+    int score_value = 0;
+
+    /* Adjust OOM killer so we're considered the least likely candidate 
+     * for killing in OOM conditions
+     */
+    char oom_adj_path[kFileNameLen];
+    snprintf(oom_adj_path, kFileNameLen - 1, OOM_SCORE_ADJ_PATH);
+    if (stat(oom_adj_path, &st) == -1) {
+        snprintf(oom_adj_path, kFileNameLen - 1, OOM_ADJ_PATH);
+        if (stat(oom_adj_path, &st) == -1) {
+            g_warning("MemoryWatcher: 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, "w");
+    if(f) {
+        fprintf(f, "%i", score_value);
+        fclose(f);
+    } else {
+        g_warning("MemoryWatcher: Failed to adjust OOM value, could not open file %s", oom_adj_path);
+    }
+}
+
 #if defined(HAS_MEMCHUTE)
 void MemoryWatcher::memchuteCallback(MemchuteThreshold threshold)
 {

Src/webbase/MemoryWatcher.h

@@ -67,6 +67,8 @@ class MemoryWatcher
 	bool timerTicked();
 	int getCurrentRssUsage() const;
 
+    void adjustOomScore();
+
 #if defined(HAS_MEMCHUTE)
     static void memchuteCallback(MemchuteThreshold threshold);
 #endif