Umap is a library that provides an mmap()-like interface to a simple, user- space page fault handler based on the userfaultfd Linux feature (starting with 4.3 linux kernel). The use case is to have an application specific buffer of pages cached from a large file, i.e. out-of-core execution using memory map.
The src directory in the top level contains the source code for the library.
The tests directory contains various tests written to test the library including a hello world program for userfaultfd based upon code from the userfaultfd-hello-world project.
LLNL-CODE-733797
Building umap is trivial. In the root directory of the repo
mkdir build
cd build
cmake -DCMAKE_INSTALL_PREFIX=<where you want the sofware> ..
make installThe default for cmake is to build a Debug version of the software. If you would like to build an optimized (-O3) version, simply run
cmake -DCMAKE_BUILD_TYPE=Release -DCMAKE_INSTALL_PREFIX=<install-dir> ..Building Umap requires a C++ compiler, CMake >= 3.5.1, as well as the Linux kernel headers.
Additionally, Umap will automatically enable read/write mode at library compile time if it detects that the installed kernel supports it by looking at the defined symbols in the kernel headers. Some Linux distributions, such as Ubuntu 20.04.2, provide a 5.8 kernel that supports read/write mode but don't ship with headers that define these symbols.
Read-only mode: Linux kernel >= 4.3
Read/write mode: Linux kernel >= 5.7 (>= 5.10 preferred)
Note: Some early mainline releases of Linux that included support for read/write mode (between 5.7 and 5.9) contain a known bug that causes an application to hang indefinitely when performing a write. It's recommended to update to a 5.10 kernel if this bug is encountered.
At runtime, Umap requires a kernel that supports the same features as it was built against. For example, running a version of Umap compiled against kernel 5.10 on a system with kernel 4.18 will result in runtime errors caused by write functionality not being present in the 4.18 kernel.
On Linux >= 5.4, the sysctl variable vm.unprivileged_userfaultfd needs to be set to 1 in order to use Umap in both read-only and read/write modes as a non-root user. The value of this variable may be determined by running sysctl vm.unprivileged_userfaultfd or cat /proc/sys/vm/unprivileged_userfaultfd.
Applications can be found at https://github.com/LLNL/umap-apps.
Both user and code documentation is available here.
If you have build problems, we have comprehensive build sytem documentation too!
Peng, I.B., Gokhale, M., Youssef, K., Iwabuchi, K. and Pearce, R., 2021. Enabling Scalable and Extensible Memory-mapped Datastores in Userspace. IEEE Transactions on Parallel and Distributed Systems. doi: 10.1109/TPDS.2021.3086302.
Peng, I.B., McFadden, M., Green, E., Iwabuchi, K., Wu, K., Li, D., Pearce, R. and Gokhale, M., 2019, November. UMap: Enabling application-driven optimizations for page management. In 2019 IEEE/ACM Workshop on Memory Centric High Performance Computing (MCHPC) (pp. 71-78). IEEE.
- The license is LGPL.
- thirdparty_licenses.md
- Ivy Peng ([email protected])
- Maya Gokhale ([email protected])
- Eric Green ([email protected])
- Abhik Sarkar ([email protected])