[MemoryPressureHandler] Unify critical/synchronous memory pressure events

Add new 'StrictSynchronous' MemoryUsagePolicy that triggers
critical and synchronous memory release when memory limit is exceeded.
This unifies memory thresholds calculation in single place.

Author: asurdej-comcast

Source/WTF/wtf/MemoryPressureHandler.cpp

@@ -165,6 +165,7 @@ static const char* toString(MemoryUsagePolicy policy)
     case MemoryUsagePolicy::Unrestricted: return "Unrestricted";
     case MemoryUsagePolicy::Conservative: return "Conservative";
     case MemoryUsagePolicy::Strict: return "Strict";
+    case MemoryUsagePolicy::StrictSynchronous: return "StrictSynchronous";
     }
     ASSERT_NOT_REACHED();
     return "";
@@ -226,6 +227,8 @@ size_t MemoryPressureHandler::thresholdForPolicy(MemoryUsagePolicy policy, Memor
         return m_configuration.conservativeThresholdFraction * (type == MemoryType::Normal ? m_configuration.baseThreshold : m_configuration.baseThresholdVideo);
     case MemoryUsagePolicy::Strict:
         return m_configuration.strictThresholdFraction * (type == MemoryType::Normal ? m_configuration.baseThreshold : m_configuration.baseThresholdVideo);
+    case MemoryUsagePolicy::StrictSynchronous:
+        return type == MemoryType::Normal ? m_configuration.baseThreshold : m_configuration.baseThresholdVideo;
     default:
         ASSERT_NOT_REACHED();
         return 0;
@@ -234,6 +237,8 @@ size_t MemoryPressureHandler::thresholdForPolicy(MemoryUsagePolicy policy, Memor
 
 MemoryUsagePolicy MemoryPressureHandler::policyForFootprints(size_t footprint, size_t 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))
         return MemoryUsagePolicy::Strict;
     if (footprint >= thresholdForPolicy(MemoryUsagePolicy::Conservative, MemoryType::Normal) || footprintVideo >= thresholdForPolicy(MemoryUsagePolicy::Conservative, MemoryType::Video))
@@ -303,15 +308,15 @@ void MemoryPressureHandler::measurementTimerFired()
         releaseMemory(Critical::No, Synchronous::No);
         break;
     case MemoryUsagePolicy::Strict:
-        if (footprint > m_configuration.baseThreshold || footprintVideo > m_configuration.baseThresholdVideo) {
-            WTFLogAlways("MemoryPressure: Critical memory usage (PID=%d) [MB]: %zu (of %zu), video: %zu (of %zu)\n",
-                          getpid(), footprint / MB, m_configuration.baseThreshold / MB,
-                          footprintVideo / MB, m_configuration.baseThresholdVideo / MB);
-            releaseMemory(Critical::Yes, Synchronous::Yes);
-            break;
-        }
         releaseMemory(Critical::Yes, Synchronous::No);
         break;
+    case MemoryUsagePolicy::StrictSynchronous:
+        WTFLogAlways("MemoryPressure: Critical memory usage (PID=%d) [MB]: %zu/%zu, video: %zu/%zu\n",
+                     getpid(),
+                     footprint / MB, m_configuration.baseThreshold / MB,
+                     footprintVideo / MB, m_configuration.baseThresholdVideo / MB);
+        releaseMemory(Critical::Yes, Synchronous::Yes);
+        break;
     }
 
     if (processState() == WebsamProcessState::Active && footprint > thresholdForMemoryKillOfInactiveProcess(m_pageCount))

Source/WTF/wtf/MemoryPressureHandler.h

@@ -59,6 +59,7 @@ enum class MemoryUsagePolicy : uint8_t {
     Unrestricted, // Allocate as much as you want
     Conservative, // Maybe you don't cache every single thing
     Strict, // Time to start pinching pennies for real
+    StrictSynchronous, // Time to start pinching pennies for real, and do it now
 };
 
 enum class MemoryType : uint8_t {