A question about transparent hugepages

according to the total_mapcount, Different process can map any subpages of the
transparent hugepages. How it can happen to ?

For anonymous memory it can only happen over copy-on-write via fork() + munmap() or something in one of the processes.

Now we have tmpfs/shmem with huge pages in mainline. In this case you can map any subpage directly from file.

 Kirill A. Shutemov