[compiler-rt] [scudo] Separated committed and decommitted entries. (PR #101409)

[via llvm-commits]

================
@@ -475,66 +506,86 @@ template <typename Config> class MapAllocatorCache {
     u32 FreeIndex = AvailableHead;
     AvailableHead = Entries[AvailableHead].Next;
 
-    if (EntriesCount == 0) {
-      LRUTail = static_cast<u16>(FreeIndex);
-    } else {
-      // Check list order
-      if (EntriesCount > 1)
-        DCHECK_GE(Entries[LRUHead].Time, Entries[Entries[LRUHead].Next].Time);
-      Entries[LRUHead].Prev = static_cast<u16>(FreeIndex);
-    }
-
     Entries[FreeIndex] = Entry;
-    Entries[FreeIndex].Next = LRUHead;
-    Entries[FreeIndex].Prev = CachedBlock::InvalidEntry;
-    LRUHead = static_cast<u16>(FreeIndex);
+    pushFront(FreeIndex, ListType);
     EntriesCount++;
 
+    if (Entries[EntryLists[ListType].Head].Next != CachedBlock::InvalidEntry) {
+      DCHECK_GE(Entries[EntryLists[ListType].Head].Time,
+                Entries[Entries[EntryLists[ListType].Head].Next].Time);
+    }
     // Availability stack should not have available entries when all entries
     // are in use
     if (EntriesCount == Config::getEntriesArraySize())
       DCHECK_EQ(AvailableHead, CachedBlock::InvalidEntry);
   }
 
-  void remove(uptr I) REQUIRES(Mutex) {
-    DCHECK(Entries[I].isValid());
-
-    Entries[I].invalidate();
-
-    if (I == LRUHead)
-      LRUHead = Entries[I].Next;
+  // Joins the entries adjacent to Entries[I], effectively
+  // unlinking Entries[I] from the list
+  void unlink(uptr I, EntryListT ListType) REQUIRES(Mutex) {
+    if (I == EntryLists[ListType].Head)
+      EntryLists[ListType].Head = Entries[I].Next;
     else
       Entries[Entries[I].Prev].Next = Entries[I].Next;
 
-    if (I == LRUTail)
-      LRUTail = Entries[I].Prev;
+    if (I == EntryLists[ListType].Tail)
+      EntryLists[ListType].Tail = Entries[I].Prev;
     else
       Entries[Entries[I].Next].Prev = Entries[I].Prev;
+  }
 
+  // Invalidates Entries[I], removes Entries[I] from list, and pushes
+  // Entries[I] onto the stack of available entries
+  void remove(uptr I, EntryListT ListType) REQUIRES(Mutex) {
+    DCHECK(Entries[I].isValid());
+
+    Entries[I].invalidate();
+
+    unlink(I, ListType);
     Entries[I].Next = AvailableHead;
     AvailableHead = static_cast<u16>(I);
     EntriesCount--;
 
     // Cache should not have valid entries when not empty
     if (EntriesCount == 0) {
-      DCHECK_EQ(LRUHead, CachedBlock::InvalidEntry);
-      DCHECK_EQ(LRUTail, CachedBlock::InvalidEntry);
+      DCHECK_EQ(EntryLists[COMMITTED].Head, CachedBlock::InvalidEntry);
+      DCHECK_EQ(EntryLists[COMMITTED].Tail, CachedBlock::InvalidEntry);
+      DCHECK_EQ(EntryLists[DECOMMITTED].Head, CachedBlock::InvalidEntry);
+      DCHECK_EQ(EntryLists[DECOMMITTED].Tail, CachedBlock::InvalidEntry);
     }
   }
 
+  inline void pushFront(uptr I, EntryListT ListType) REQUIRES(Mutex) {
+    if (EntryLists[ListType].Tail == CachedBlock::InvalidEntry)
+      EntryLists[ListType].Tail = static_cast<u16>(I);
----------------
ChiaHungDuan wrote:

In this case, it's an empty list and we need to update both Head and Tail

https://github.com/llvm/llvm-project/pull/101409