https://android.googlesource.com/kernel/common/+/3b4ff5af8d36f391ee0e6adf7b9d14d0d004de95/arch/s390/hypfs/hypfs_vm.c
arch/s390/hypfs/hypfs_vm.c - kernel/common - Git at Google
archvmkernelcommongit
https://www.ibm.com/docs/en/linux-on-systems?topic=hypfs-hypfsa2406e
hypfs.a2406e