public int allocateFromDiscard(MemoryBuffer[] dest, int destIx,
        int headerIx, int freeListIx, int allocationSize) {
      LlapAllocatorBuffer buffer = (LlapAllocatorBuffer)dest[destIx];
      initializeNewlyAllocated(buffer, allocationSize, headerIx, offsetFromHeaderIndex(headerIx));
      if (assertsEnabled) {
        checkHeader(headerIx, freeListIx, true);
      }
      setHeaderAlloc(headerIx, freeListIx, buffer, CasLog.Src.ALLOC_DEFRAG);
      return destIx + 1;
    }
Allocates into an empty block obtained via a forced eviction. Same args as allocateFast.
llap-server/src/java/org/apache/hadoop/hive/llap/cache/BuddyAllocator.java