diff --git a/Source/WebCore/ChangeLog b/Source/WebCore/ChangeLog
index f47c526..33918e9 100644
--- a/Source/WebCore/ChangeLog
+++ b/Source/WebCore/ChangeLog
@@ -1,3 +1,19 @@
+2019-10-16  Chris Dumez  <cdumez@apple.com>
+
+        [WK2] Handle back/forward cache entry expiration in the UIProcess instead of the WebProcess
+        https://bugs.webkit.org/show_bug.cgi?id=203034
+        <rdar://problem/56332453>
+
+        Reviewed by Antti Koivisto.
+
+        Use Seconds type for backForwardCacheExpirationInterval setting instead of
+        double, for clarity.
+
+        * history/CachedPage.cpp:
+        (WebCore::CachedPage::CachedPage):
+        (WebCore::CachedPage::hasExpired const):
+        * page/Settings.yaml:
+
 2019-10-16  Zalan Bujtas  <zalan@apple.com>
 
         [LFC][IFC] Fix various vertical alignment issues.
diff --git a/Source/WebCore/history/CachedPage.cpp b/Source/WebCore/history/CachedPage.cpp
index 9747a40..08af39d 100644
--- a/Source/WebCore/history/CachedPage.cpp
+++ b/Source/WebCore/history/CachedPage.cpp
@@ -55,7 +55,7 @@
 
 CachedPage::CachedPage(Page& page)
     : m_page(page)
-    , m_expirationTime(MonotonicTime::now() + Seconds(page.settings().backForwardCacheExpirationInterval()))
+    , m_expirationTime(MonotonicTime::now() + page.settings().backForwardCacheExpirationInterval())
     , m_cachedMainFrame(makeUnique<CachedFrame>(page.mainFrame()))
 {
 #ifndef NDEBUG
diff --git a/Source/WebCore/page/Settings.yaml b/Source/WebCore/page/Settings.yaml
index 0ae7742..47f0ed6 100644
--- a/Source/WebCore/page/Settings.yaml
+++ b/Source/WebCore/page/Settings.yaml
@@ -422,8 +422,8 @@
   initial: false
 
 backForwardCacheExpirationInterval:
-  type: double
-  initial: 1800
+  type: Seconds
+  initial: 30_min
 
 # Some apps could have a default video poster if it is not set.
 defaultVideoPosterURL:
diff --git a/Source/WebKit/ChangeLog b/Source/WebKit/ChangeLog
index 15ecc37..4ffcebb 100644
--- a/Source/WebKit/ChangeLog
+++ b/Source/WebKit/ChangeLog
@@ -1,5 +1,30 @@
 2019-10-16  Chris Dumez  <cdumez@apple.com>
 
+        [WK2] Handle back/forward cache entry expiration in the UIProcess instead of the WebProcess
+        https://bugs.webkit.org/show_bug.cgi?id=203034
+        <rdar://problem/56332453>
+
+        Reviewed by Antti Koivisto.
+
+        Handle back/forward cache entry expiration in the UIProcess instead of the WebProcess,
+        now that back/forward cache management is done in the UIProcess.
+
+        * UIProcess/WebBackForwardCacheEntry.cpp:
+        (WebKit::WebBackForwardCacheEntry::WebBackForwardCacheEntry):
+        (WebKit::WebBackForwardCacheEntry::takeSuspendedPage):
+        (WebKit::WebBackForwardCacheEntry::expirationTimerFired):
+        * UIProcess/WebBackForwardCacheEntry.h:
+        Add a Timer to WebBackForwardCacheEntry to make the entry expire after 30 minutes, which is what used
+        to happen on WebContent process side. One difference in behavior is that when the entry expires we
+        now remove it from the cache right away to free-up memory, instead of simply refusing to use it later
+        on.
+
+        * WebProcess/WebPage/WebPage.cpp:
+        Disable back forward cache expiration in the WebContent process when using modern
+        WebKit.
+
+2019-10-16  Chris Dumez  <cdumez@apple.com>
+
         [iOS] Stop terminating the prewarmed process on application suspension
         https://bugs.webkit.org/show_bug.cgi?id=203033
 
diff --git a/Source/WebKit/UIProcess/WebBackForwardCacheEntry.cpp b/Source/WebKit/UIProcess/WebBackForwardCacheEntry.cpp
index 75cdfb6..59fbed5 100644
--- a/Source/WebKit/UIProcess/WebBackForwardCacheEntry.cpp
+++ b/Source/WebKit/UIProcess/WebBackForwardCacheEntry.cpp
@@ -26,18 +26,24 @@
 #include "config.h"
 #include "WebBackForwardCacheEntry.h"
 
+#include "Logging.h"
 #include "SuspendedPageProxy.h"
+#include "WebBackForwardCache.h"
 #include "WebProcessMessages.h"
 #include "WebProcessProxy.h"
 
 namespace WebKit {
 
+static const Seconds expirationDelay { 30_min };
+
 WebBackForwardCacheEntry::WebBackForwardCacheEntry(WebBackForwardCache& backForwardCache, WebCore::BackForwardItemIdentifier backForwardItemID, WebCore::ProcessIdentifier processIdentifier, std::unique_ptr<SuspendedPageProxy>&& suspendedPage)
     : m_backForwardCache(backForwardCache)
     , m_processIdentifier(processIdentifier)
     , m_backForwardItemID(backForwardItemID)
     , m_suspendedPage(WTFMove(suspendedPage))
+    , m_expirationTimer(RunLoop::main(), this, &WebBackForwardCacheEntry::expirationTimerFired)
 {
+    m_expirationTimer.startOneShot(expirationDelay);
 }
 
 WebBackForwardCacheEntry::~WebBackForwardCacheEntry()
@@ -52,6 +58,7 @@
 {
     ASSERT(m_suspendedPage);
     m_backForwardItemID = { };
+    m_expirationTimer.stop();
     return std::exchange(m_suspendedPage, nullptr);
 }
 
@@ -63,4 +70,13 @@
     return *process;
 }
 
+void WebBackForwardCacheEntry::expirationTimerFired()
+{
+    RELEASE_LOG(BackForwardCache, "%p - WebBackForwardCacheEntry::expirationTimerFired backForwardItemID: %s, hasSuspendedPage? %d", this, m_backForwardItemID.string().utf8().data(), !!m_suspendedPage);
+    ASSERT(m_backForwardItemID);
+    auto* item = WebBackForwardListItem::itemForID(m_backForwardItemID);
+    ASSERT(item);
+    m_backForwardCache.removeEntry(*item); // Will destroy |this|.
+}
+
 } // namespace WebKit
diff --git a/Source/WebKit/UIProcess/WebBackForwardCacheEntry.h b/Source/WebKit/UIProcess/WebBackForwardCacheEntry.h
index 1f4c6a5..835a234 100644
--- a/Source/WebKit/UIProcess/WebBackForwardCacheEntry.h
+++ b/Source/WebKit/UIProcess/WebBackForwardCacheEntry.h
@@ -28,6 +28,7 @@
 #include <WebCore/BackForwardItemIdentifier.h>
 #include <WebCore/ProcessIdentifier.h>
 #include <wtf/Forward.h>
+#include <wtf/RunLoop.h>
 
 namespace WebKit {
 
@@ -49,10 +50,13 @@
     WebProcessProxy& process() const;
 
 private:
+    void expirationTimerFired();
+
     WebBackForwardCache& m_backForwardCache;
     WebCore::ProcessIdentifier m_processIdentifier;
     WebCore::BackForwardItemIdentifier m_backForwardItemID;
     std::unique_ptr<SuspendedPageProxy> m_suspendedPage;
+    RunLoop::Timer<WebBackForwardCacheEntry> m_expirationTimer;
 };
 
 } // namespace WebKit
diff --git a/Source/WebKit/WebProcess/WebPage/WebPage.cpp b/Source/WebKit/WebProcess/WebPage/WebPage.cpp
index 15cd623..0817927 100644
--- a/Source/WebKit/WebProcess/WebPage/WebPage.cpp
+++ b/Source/WebKit/WebProcess/WebPage/WebPage.cpp
@@ -521,6 +521,10 @@
     m_page->settings().setScrollingCoordinatorEnabled(m_useAsyncScrolling);
 #endif
 
+    // Disable Back/Forward cache expiration in the WebContent process since management happens in the UIProcess
+    // in modern WebKit.
+    m_page->settings().setBackForwardCacheExpirationInterval(Seconds::infinity());
+
     m_mainFrame = WebFrame::createWithCoreMainFrame(this, &m_page->mainFrame());
     m_drawingArea->updatePreferences(parameters.store);
 
diff --git a/Source/WebKitLegacy/mac/ChangeLog b/Source/WebKitLegacy/mac/ChangeLog
index 9ef9a70..061ae1b 100644
--- a/Source/WebKitLegacy/mac/ChangeLog
+++ b/Source/WebKitLegacy/mac/ChangeLog
@@ -1,3 +1,14 @@
+2019-10-16  Chris Dumez  <cdumez@apple.com>
+
+        [WK2] Move back/forward cache entry expiration from the WebProcess to the UIProcess
+        https://bugs.webkit.org/show_bug.cgi?id=203034
+        <rdar://problem/56332453>
+
+        Reviewed by Antti Koivisto.
+
+        * WebView/WebView.mm:
+        (-[WebView _preferencesChanged:]):
+
 2019-10-15  Chris Dumez  <cdumez@apple.com>
 
         [macOS] Simplify main thread initialization
diff --git a/Source/WebKitLegacy/mac/WebView/WebView.mm b/Source/WebKitLegacy/mac/WebView/WebView.mm
index 830d216..4886c84 100644
--- a/Source/WebKitLegacy/mac/WebView/WebView.mm
+++ b/Source/WebKitLegacy/mac/WebView/WebView.mm
@@ -2913,7 +2913,7 @@
     settings.setDOMPasteAllowed([preferences isDOMPasteAllowed]);
     settings.setUsesPageCache([self usesPageCache]);
     settings.setPageCacheSupportsPlugins([preferences pageCacheSupportsPlugins]);
-    settings.setBackForwardCacheExpirationInterval([preferences _backForwardCacheExpirationInterval]);
+    settings.setBackForwardCacheExpirationInterval(Seconds { [preferences _backForwardCacheExpirationInterval] });
 
     settings.setDeveloperExtrasEnabled([preferences developerExtrasEnabled]);
     settings.setJavaScriptRuntimeFlags(JSC::RuntimeFlags([preferences javaScriptRuntimeFlags]));