MMTk ART Binding

This repository allows MMTk to work with the Android Runtime (ART).

This repository hosts the MMTk-side of the binding. Our ART fork hosts the ART-side of the binding as well as any changes required to ART to allow MMTk to work. Our MMTk fork hosts changes to MMTk that are required to allow MMTk to work with ART.

Current Status

We support the NoGC, SemiSpace, Immix, StickyImmix, GenImmix, and GenCopy plans in MMTk core.

We can run headless ART builds both on target and host and for both x86_64 and aarch64 devices. NoGC is only supported for headless ART builds.

We have allocation fast-paths implemented for all architectures.

We can boot an AOSP build on an x86_64 Cuttlefish VM with the SemiSpace, Immix, and StickyImmix plans. We can boot an AOSP build on an actual arm64 device with the SemiSpace, Immix, and StickyImmix plans.

Building and Installation Instructions

Setting up

Since we had to add/change repositories to get MMTk to build with ART, we maintain our own repo manifest file. It is based off the master-art manifest file. We lock all versions of dependencies to ensure we can always build MMTk. The ART fork is based on commit 451cfcf9d09515ef60d76bd8551fc68c6e3bf621.

$ mkdir android-mmtk
$ cd android-mmtk
$ repo init -u https://github.com/k-sareen/mmtk-art-manifest -b mmtk-art

Building

Building Headless ART

Set up the environment and build target.

$ source build/envsetup.sh
$ export VARIANT="eng"
$ lunch silvermont-trunk_staging-${VARIANT}  # For Linux x86_64 host builds

OR for aarch64 device target:

$ lunch armv8-trunk_staging-${VARIANT}       # For device target builds

If you want a release/performance build set the VARIANT environment variable to userdebug or user.

Note: If you want MMTk to build in release mode as well, then you will have to comment out the debug build flags in mmtk-core/Android.bp and uncomment the release build flags in mmtk-core/Android.bp as well as mmtk-art/Android.bp.

To build MMTk ART with Immix:

$ RUST_BACKTRACE=1 ART_USE_MMTK=true ART_USE_READ_BARRIER=false ART_USE_WRITE_BARRIER=false ART_DEFAULT_GC_TYPE=SS ./art/tools/buildbot-build.sh --{host,target} --installclean --skip-run-tests-build

To build MMTk ART with StickyImmix:

$ RUST_BACKTRACE=1 ART_USE_MMTK=true ART_USE_READ_BARRIER=false ART_USE_WRITE_BARRIER=true ART_DEFAULT_GC_TYPE=SS ./art/tools/buildbot-build.sh --{host,target} --installclean --skip-run-tests-build

Building ART APEX

Set up the environment and build target.

$ source build/envsetup.sh
$ export VARIANT="eng"
$ banchan com.android.art ${VARIANT} x86_64    # For x86_64 target builds

OR for aarch64 device target:

$ banchan com.android.art ${VARIANT} arm64     # For arm64 target builds

See above if you want a release/performance build.

To build MMTk ART with Immix:

$ RUST_BACKTRACE=1 ART_USE_MMTK=1 ART_USE_READ_BARRIER=false ART_USE_WRITE_BARRIER=false ART_DEFAULT_GC_TYPE=SS m apps_only dist

To build MMTk ART with StickyImmix:

$ RUST_BACKTRACE=1 ART_USE_MMTK=1 ART_USE_READ_BARRIER=false ART_USE_WRITE_BARRIER=true ART_DEFAULT_GC_TYPE=SS m apps_only dist

Profile Guided Optimization

MMTk core does not use any inline attributes to avoid second guessing the compiler. We've found that (ab)using inline attributes can lead to performance degradation as well. To that end, we use profile guided optimization (PGO) to inform the inlining decisions of the compiler.

We provide PGO profiles under the profiles/ directory for the supported plans for both headless and APEX builds. If you want to enable PGO builds, you will have to add the profile file to the build command in the Android.bp file. Note that unfortunately due to how Android invokes rustc and a Rust compiler bug, we can't use the -C linker-plugin-lto flag as it triggers the bug. We have currently disabled it for our PGO builds.

Installation

Cuttlefish VM

We use Cuttlefish images from this Android CI build.

We run the Cuttlefish VM like so:

$ HOME=$PWD taskset -c 0-3 ./bin/launch_cvd -report_anonymous_usage_stats=n --daemon --gpu_mode=guest_swiftshader -vm_manager=qemu_cli -cpus=4

QEMU was used since crosvm was crashing on our development machines. It is likely MMTk works with crosvm but it is untested.

Install ART with adb like so:

$ adb install /path/to/android/root/out/dist/com.android.art.apex
$ adb reboot

If everything is fine then you should boot into the Android lock screen.

Running

You can check if you are using MMTk if it is printing logs in logcat like so:

$ adb logcat | grep "mmtk-art"
[...]
08-01 12:18:58.734  1025  1251 I mmtk-art64: mmtk::util::heap::gc_trigger: [POLL] immix: Triggering collection (7722/7721 pages)
08-01 12:18:58.736  1025  1039 I mmtk-art64: mmtk::plan::sticky::immix::global: Full heap GC
08-01 12:18:58.818  1025  1039 I mmtk-art64: mmtk::scheduler::scheduler: End of GC (7328/7991 pages, took 81 ms)
08-01 12:22:49.812  1025  1063 I mmtk-art64: mmtk::util::heap::gc_trigger: [POLL] immix: Triggering collection (7994/7991 pages)
08-01 12:22:49.814  1025  1040 I mmtk-art64: mmtk::plan::sticky::immix::global: Nursery GC
08-01 12:22:49.838  1025  1040 I mmtk-art64: mmtk::scheduler::scheduler: End of GC (7385/7991 pages, took 24 ms)
[...]

Known Limitations

From the generational plans, only StickyImmix is currently supported for APEX builds as the others do not have support for the ZygoteSpace yet.

We've temporarily disabled loading app images at run-time since we currently do not have a way to remove image spaces inside MMTk. Once we have this functionality, we will enable this feature and register app images with MMTk.

The port has not been performance tuned at all. For example, currently the write barrier is a full call into MMTk even for the fast-path.