Enforce foreground WebContent memory limit on macOS

https://bugs.webkit.org/show_bug.cgi?id=240397

Reviewed by Chris Dumez.

We removed the foreground memory limit for WebContent on macOS in r272046. But based on some
bug reports that we've seen, it seems like we need to restore some limit to prevent bad user
outcomes when a misbehaving process has runaway memory usage.

This patch adds a foreground memory limit of 8GB or 16GB depending on RAM size. This matches
the limits set by other browsers for their content process.

* wtf/MemoryPressureHandler.cpp:
(WTF::thresholdForMemoryKillOfActiveProcess):
(WTF::MemoryPressureHandler::thresholdForMemoryKill):

Canonical link: https://commits.webkit.org/250548@main
git-svn-id: https://svn.webkit.org/repository/webkit/trunk@294181 268f45cc-cd09-0410-ab3c-d52691b4dbfc

Source/WTF/ChangeLog

@@ -53,6 +53,24 @@
 
         * wtf/cocoa/RuntimeApplicationChecksCocoa.h:
 
+2022-05-13  Ben Nham  <nham@apple.com>
+
+        Enforce foreground WebContent memory limit on macOS
+        https://bugs.webkit.org/show_bug.cgi?id=240397
+
+        Reviewed by Chris Dumez.
+
+        We removed the foreground memory limit for WebContent on macOS in r272046. But based on some
+        bug reports that we've seen, it seems like we need to restore some limit to prevent bad user
+        outcomes when a misbehaving process has runaway memory usage.
+
+        This patch adds a foreground memory limit of 8GB or 16GB depending on RAM size. This matches
+        the limits set by other browsers for their content process.
+
+        * wtf/MemoryPressureHandler.cpp:
+        (WTF::thresholdForMemoryKillOfActiveProcess):
+        (WTF::MemoryPressureHandler::thresholdForMemoryKill):
+
 2022-05-10  Brent Fulgham  <bfulgham@apple.com>
 
         Remove abandoned CSSDeferredParser implementation and feature flag

Source/WTF/wtf/MemoryPressureHandler.cpp

@@ -95,6 +95,12 @@ static const char* toString(MemoryUsagePolicy policy)
 }
 #endif
 
+static size_t thresholdForMemoryKillOfActiveProcess(unsigned tabCount)
+{
+    size_t baseThreshold = ramSize() > 16 * GB ? 15 * GB : 7 * GB;
+    return baseThreshold + tabCount * GB;
+}
+
 static size_t thresholdForMemoryKillOfInactiveProcess(unsigned tabCount)
 {
 #if CPU(X86_64) || CPU(ARM64)
@@ -121,7 +127,7 @@ std::optional<size_t> MemoryPressureHandler::thresholdForMemoryKill()
     case WebsamProcessState::Inactive:
         return thresholdForMemoryKillOfInactiveProcess(m_pageCount);
     case WebsamProcessState::Active:
-        break;
+        return thresholdForMemoryKillOfActiveProcess(m_pageCount);
     }
     return std::nullopt;
 }