Bug 610417 - Optimize eviction in bfcache. r=smaug a=blocking-fennec

browser/app/profile/firefox.js

@@ -907,6 +907,8 @@ pref("browser.shell.checkDefaultBrowser", false);
 // disable bfcache for memory
 pref("browser.sessionhistory.max_total_viewers", 0);
 
+pref("browser.sessionhistory.optimize_eviction", false);
+
 // tweak default content sink prefs
 pref("content.sink.interactive_deflect_count", 10); /* default 0 */
 pref("content.sink.perf_deflect_count", 50); /* default 200 */

docshell/shistory/public/nsISHEntry.idl

@@ -250,11 +250,16 @@ interface nsISHEntry : nsIHistoryEntry
     attribute unsigned long long docshellID;
 };
 
-[scriptable, uuid(e0b0ac6d-cb29-4be2-b685-1755d6301a69)]
+[scriptable, uuid(bb66ac35-253b-471f-a317-3ece940f04c5)]
 interface nsISHEntryInternal : nsISupports
 {
     [notxpcom] void RemoveFromBFCacheAsync();
     [notxpcom] void RemoveFromBFCacheSync();
+
+    /**
+     * A number that is assigned by the sHistory when the entry is activated
+     */
+    attribute unsigned long lastTouched;
 };
 
 %{ C++

docshell/shistory/src/nsSHEntry.cpp

@@ -117,6 +117,7 @@ nsSHEntry::nsSHEntry()
   , mParent(nsnull)
   , mViewerBounds(0, 0, 0, 0)
   , mDocShellID(0)
+  , mLastTouched(0)
 {
 }
 
@@ -998,3 +999,18 @@ nsSHEntry::SetDocshellID(PRUint64 aID)
   return NS_OK;
 }
 
+
+NS_IMETHODIMP
+nsSHEntry::GetLastTouched(unsigned int *aLastTouched)
+{
+  *aLastTouched = mLastTouched;
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsSHEntry::SetLastTouched(unsigned int aLastTouched)
+{
+  mLastTouched = aLastTouched;
+  return NS_OK;
+}
+

docshell/shistory/src/nsSHEntry.h

@@ -120,6 +120,7 @@ private:
   nsAutoPtr<nsDocShellEditorData> mEditorData;
   nsString                        mStateData;
   PRUint64                        mDocShellID;
+  PRUint32                        mLastTouched;
 };
 
 #endif /* nsSHEntry_h */

docshell/shistory/src/nsSHistory.cpp

@@ -70,6 +70,7 @@
 
 #define PREF_SHISTORY_SIZE "browser.sessionhistory.max_entries"
 #define PREF_SHISTORY_MAX_TOTAL_VIEWERS "browser.sessionhistory.max_total_viewers"
+#define PREF_SHISTORY_OPTIMIZE_EVICTION "browser.sessionhistory.optimize_eviction"
 
 static PRInt32  gHistoryMaxSize = 50;
 // Max viewers allowed per SHistory objects
@@ -80,6 +81,16 @@ static PRCList gSHistoryList;
 // means we will calculate how many viewers to cache based on total memory
 PRInt32 nsSHistory::sHistoryMaxTotalViewers = -1;
 
+// Whether we should optimize the search for which entry to evict,
+// by evicting older entries first. See entryLastTouched in
+// nsSHistory::EvictGlobalContentViewer().
+// NB: After 4.0, we should remove this option and the corresponding
+//     pref - optimization should always be used
+static PRBool gOptimizeEviction = PR_FALSE;
+// A counter that is used to be able to know the order in which
+// entries were touched, so that we can evict older entries first.
+static PRUint32 gTouchCounter = 0;
+
 enum HistCmd{
   HIST_CMD_BACK,
   HIST_CMD_FORWARD,
@@ -222,6 +233,8 @@ nsSHistory::UpdatePrefs(nsIPrefBranch *aPrefBranch)
   aPrefBranch->GetIntPref(PREF_SHISTORY_SIZE, &gHistoryMaxSize);
   aPrefBranch->GetIntPref(PREF_SHISTORY_MAX_TOTAL_VIEWERS,
                           &sHistoryMaxTotalViewers);
+  aPrefBranch->GetBoolPref(PREF_SHISTORY_OPTIMIZE_EVICTION,
+                          &gOptimizeEviction);
   // If the pref is negative, that means we calculate how many viewers
   // we think we should cache, based on total memory
   if (sHistoryMaxTotalViewers < 0) {
@@ -265,6 +278,8 @@ nsSHistory::Startup()
       branch->AddObserver(PREF_SHISTORY_SIZE, obs, PR_FALSE);
       branch->AddObserver(PREF_SHISTORY_MAX_TOTAL_VIEWERS,
                           obs, PR_FALSE);
+      branch->AddObserver(PREF_SHISTORY_OPTIMIZE_EVICTION,
+                          obs, PR_FALSE);
 
       nsCOMPtr<nsIObserverService> obsSvc =
         mozilla::services::GetObserverService();
@@ -937,6 +952,7 @@ nsSHistory::EvictGlobalContentViewer()
     // farthest from the current focus in any SHistory object.  The
     // ContentViewer associated with that SHEntry will be evicted
     PRInt32 distanceFromFocus = 0;
+    PRUint32 candidateLastTouched = 0;
     nsCOMPtr<nsISHEntry> evictFromSHE;
     nsCOMPtr<nsIContentViewer> evictViewer;
     PRInt32 totalContentViewers = 0;
@@ -961,6 +977,15 @@ nsSHistory::EvictGlobalContentViewer()
         entry->GetAnyContentViewer(getter_AddRefs(ownerEntry),
                                    getter_AddRefs(viewer));
 
+        PRUint32 entryLastTouched = 0;
+        if (gOptimizeEviction) {
+          nsCOMPtr<nsISHEntryInternal> entryInternal = do_QueryInterface(entry);
+          if (entryInternal) {
+            // Find when this entry was last activated
+            entryInternal->GetLastTouched(&entryLastTouched);
+          }
+        }
+
 #ifdef DEBUG_PAGE_CACHE
         nsCOMPtr<nsIURI> uri;
         if (ownerEntry) {
@@ -985,12 +1010,16 @@ nsSHistory::EvictGlobalContentViewer()
           printf("mIndex: %d i: %d\n", shist->mIndex, i);
 #endif
           totalContentViewers++;
-          if (distance > distanceFromFocus) {
-            
+
+          // If this entry is further away from focus than any previously found
+          // or at the same distance but it is longer time since it was activated
+          // then take this entry as the new candiate for eviction
+          if (distance > distanceFromFocus || (distance == distanceFromFocus && candidateLastTouched > entryLastTouched)) {
+
 #ifdef DEBUG_PAGE_CACHE
             printf("Choosing as new eviction candidate: %s\n", spec.get());
 #endif
-
+            candidateLastTouched = entryLastTouched;
             distanceFromFocus = distance;
             evictFromSHE = ownerEntry;
             evictViewer = viewer;
@@ -1404,7 +1433,6 @@ NS_IMETHODIMP
 nsSHistory::LoadEntry(PRInt32 aIndex, long aLoadType, PRUint32 aHistCmd)
 {
   nsCOMPtr<nsIDocShell> docShell;
-  nsCOMPtr<nsISHEntry> shEntry;
   // Keep note of requested history index in mRequestedIndex.
   mRequestedIndex = aIndex;
 
@@ -1419,6 +1447,13 @@ nsSHistory::LoadEntry(PRInt32 aIndex, long aLoadType, PRUint32 aHistCmd)
     return NS_ERROR_FAILURE;
   }
 
+  // Remember that this entry is getting loaded at this point in the sequence
+  nsCOMPtr<nsISHEntryInternal> entryInternal = do_QueryInterface(nextEntry);
+
+  if (entryInternal) {
+    entryInternal->SetLastTouched(++gTouchCounter);
+  }
+
   // Send appropriate listener notifications
   PRBool canNavigate = PR_TRUE;
   // Get the uri for the entry we are about to visit

modules/libpref/src/init/all.js

@@ -105,6 +105,8 @@ pref("dom.indexedDB.warningQuota", 50);
 // of content viewers to cache based on the amount of available memory.
 pref("browser.sessionhistory.max_total_viewers", -1);
 
+pref("browser.sessionhistory.optimize_eviction", false);
+
 pref("ui.use_native_colors", true);
 pref("ui.use_native_popup_windows", false);
 pref("ui.click_hold_context_menus", false);