Hack ReadFileFast() to raise the threshold of memory mapped files (from 4->12 pages).

This is a temporary solution to avoid running out of file descriptors (which defaults to 256).

Need to benchmark to understand the speed benefit. If the benefit is small, the simple solution is to avoid memory mapping files. If the benefit is significant, more thought is necessary.

llvm-svn: 48991

clang/lib/Basic/SourceManager.cpp

@@ -51,7 +51,7 @@ static const MemoryBuffer *ReadFileFast(const FileEntry *FileEnt) {
 #endif
   
   // If the file is larger than some threshold, use 'read', otherwise use mmap.
-  if (FileEnt->getSize() >= 4096*4)
+  if (FileEnt->getSize() >= 4096*12)
     return MemoryBuffer::getFile(FileEnt->getName(), strlen(FileEnt->getName()),
                                  0, FileEnt->getSize());