[MemoryPressureHandler] Subtract GPU memory from RSS when deciding memory policy

On Mali GPU drivers GPU memory is also included in process RSS mem (RSSFile)
that cause pressure handler to kick in too early comparing to other devices.
GPU memory doesn't increase container's total mem usage in cgroups
so this change doesn't affect total memory allowance but delays pressure handler only.

Author: asurdej-comcast

Source/WTF/wtf/MemoryPressureHandler.cpp

@@ -54,6 +54,7 @@ static const Seconds s_pollInterval = 30_s;
 // platform component. It's a text file containing an unsigned integer value.
 static String s_GPUMemoryFile;
 static ssize_t s_envBaseThresholdVideo = 0;
+static bool s_videoMemoryInFootprint = false;
 
 static bool isWebProcess()
 {
@@ -140,6 +141,9 @@ MemoryPressureHandler::MemoryPressureHandler()
             if (s_envBaseThresholdVideo)
                 m_configuration.baseThresholdVideo = s_envBaseThresholdVideo;
         }
+        String gpuInRSS = String::fromLatin1(getenv("WPE_POLL_GPU_IN_FOOTPRINT"));
+        if (gpuInRSS == String::fromLatin1("1") || gpuInRSS.convertToASCIILowercase() == String::fromLatin1("true"))
+            s_videoMemoryInFootprint = true;
     }
 }
 
@@ -237,6 +241,7 @@ size_t MemoryPressureHandler::thresholdForPolicy(MemoryUsagePolicy policy, Memor
 
 MemoryUsagePolicy MemoryPressureHandler::policyForFootprints(size_t footprint, size_t footprintVideo)
 {
+    footprint = calculateFootprintForPolicyDecision(footprint, footprintVideo);
     if (footprint >= thresholdForPolicy(MemoryUsagePolicy::StrictSynchronous, MemoryType::Normal) || footprintVideo >= thresholdForPolicy(MemoryUsagePolicy::StrictSynchronous, MemoryType::Video))
         return MemoryUsagePolicy::StrictSynchronous;
     if (footprint >= thresholdForPolicy(MemoryUsagePolicy::Strict, MemoryType::Normal) || footprintVideo >= thresholdForPolicy(MemoryUsagePolicy::Strict, MemoryType::Video))
@@ -246,6 +251,16 @@ MemoryUsagePolicy MemoryPressureHandler::policyForFootprints(size_t footprint, s
     return MemoryUsagePolicy::Unrestricted;
 }
 
+size_t MemoryPressureHandler::calculateFootprintForPolicyDecision(size_t footprint, size_t footprintVideo)
+{
+    // Some devices accounts video memory into the process memory footprint (as file mappings - RSSFile).
+    // In such cases, we need to subtract the video memory from the process memory footprint
+    // to make the memory pressure policy decision based on the process memory footprint only.
+    if (s_videoMemoryInFootprint)
+        footprint -= footprintVideo;
+    return footprint;
+}
+
 MemoryUsagePolicy MemoryPressureHandler::currentMemoryUsagePolicy()
 {
     return policyForFootprints(memoryFootprint(), memoryFootprintVideo());
@@ -311,9 +326,9 @@ void MemoryPressureHandler::measurementTimerFired()
         releaseMemory(Critical::Yes, Synchronous::No);
         break;
     case MemoryUsagePolicy::StrictSynchronous:
-        WTFLogAlways("MemoryPressure: Critical memory usage (PID=%d) [MB]: %zu/%zu, video: %zu/%zu\n",
+        WTFLogAlways("MemoryPressure: Critical memory usage (PID=%d) [MB]: %zu%s/%zu, video: %zu/%zu\n",
                      getpid(),
-                     footprint / MB, m_configuration.baseThreshold / MB,
+                     footprint / MB, s_videoMemoryInFootprint ? "(including video)" : "", m_configuration.baseThreshold / MB,
                      footprintVideo / MB, m_configuration.baseThresholdVideo / MB);
         releaseMemory(Critical::Yes, Synchronous::Yes);
         break;

Source/WTF/wtf/MemoryPressureHandler.h

@@ -244,6 +244,7 @@ class MemoryPressureHandler {
     std::optional<size_t> thresholdForMemoryKill(MemoryType);
     size_t thresholdForPolicy(MemoryUsagePolicy, MemoryType);
     MemoryUsagePolicy policyForFootprints(size_t, size_t);
+    size_t calculateFootprintForPolicyDecision(size_t footprint, size_t footprintVideo);
 
     void memoryPressureStatusChanged();