[compiler-rt] [scudo] Add partial chunk heuristic to retrieval algorithm. (PR #104807)

[via llvm-commits]

================
@@ -336,6 +337,37 @@ TEST_F(MapAllocatorCacheTest, CacheOrder) {
     MemMap.unmap();
 }
 
+TEST_F(MapAllocatorCacheTest, PartialChunkHeuristicRetrievalTest) {
+  const scudo::uptr MaxUnusedCacheBytes = scudo::MaxUnusedCachePages * PageSize;
+  const scudo::uptr FragmentedBytes =
+      MaxUnusedCacheBytes +
+      scudo::roundDown(scudo::CachedBlock::ReleaseMemoryUpperBound, PageSize);
+
+  scudo::uptr MaxAllowedFragmentedBytes;
+  scudo::uptr EntryHeaderPos;
+  scudo::CachedBlock Entry;
+  scudo::MemMapT MemMap = allocate(PageSize + FragmentedBytes);
+  Cache->store(Options, MemMap.getBase(), MemMap.getCapacity(),
+               MemMap.getBase(), MemMap);
+
+  // FragmentedBytes > MaxAllowedFragmentedBytes so PageSize
+  // cannot be retrieved from the cache
+  MaxAllowedFragmentedBytes = 0;
+  Entry = Cache->retrieve(MaxAllowedFragmentedBytes, PageSize, PageSize, 0,
+                          EntryHeaderPos);
----------------
ChiaHungDuan wrote:

How about
```suggestion
  Entry = Cache->retrieve(/*MaxAllowedFragmentedBytes=*/0, PageSize, PageSize, 0,
                          EntryHeaderPos);
``
and just use `FragmentedBytes` below,

https://github.com/llvm/llvm-project/pull/104807