Googlers, for design doc see: http://go/heapprofd-design
heapprofd requires Android Q.
heapprofd is a tool that tracks native heap allocations & deallocations of an Android process within a given time period. The resulting profile can be used to attribute memory usage to particular function callstacks, supporting a mix of both native and java code. The tool should be useful to Android platform developers, and app developers investigating memory issues.
On debug Android builds, you can profile all apps and most system services. On “user” builds, you can only use it on apps with the debuggable or profileable manifest flag.
Use the tools/heap_profile script to heap profile a process. If you are having trouble make sure you are using the latest version.
See all the arguments using tools/heap_profile -h, or use the defaults and just profile a process (e.g. system_server):
$ tools/heap_profile --name system_server Profiling active. Press Ctrl+C to terminate. ^CWrote profiles to /tmp/heap_profile-XSKcZ3i (symlink /tmp/heap_profile-latest) These can be viewed using pprof. Googlers: head to pprof/ and upload them.
This will create a pprof-compatible heap dump when Ctrl+C is pressed.
The resulting profile proto contains four views on the data
Googlers: Head to http://pprof/ and upload the gzipped protos to get a visualization. Tip: you might want to put libart.so as a “Hide regex” when profiling apps.
Speedscope can also be used to visualize the heap dump, but will only show the space view. Tip: Click Left Heavy on the top left for a good visualisation.
heapprofd samples heap allocations. Given a sampling interval of n bytes, one allocation is sampled, on average, every n bytes allocated. This allows to reduce the performance impact on the target process. The default sampling rate is 4096 bytes.
The easiest way to reason about this is to imagine the memory allocations as a steady stream of one byte allocations. From this stream, every n-th byte is selected as a sample, and the corresponding allocation gets attributed the complete n bytes. As an optimization, we sample allocations larger than the sampling interval with their true size.
To make this statistically more meaningful, Poisson sampling is employed. Instead of a static parameter of n bytes, the user can only choose the mean value around which the interval is distributed. This makes sure frequent small allocations get sampled as well as infrequent large ones.
When a profile session names processes by name and a matching process is started, it gets profiled from the beginning. The resulting profile will contain all allocations done between the start of the process and the end of the profiling session.
On Android, Java apps are usually not started, but the zygote forks and then specializes into the desired app. If the app's name matches a name specified in the profiling session, profiling will be enabled as part of the zygote specialization. The resulting profile contains all allocations done between that point in zygote specialization and the end of the profiling session. Some allocations done early in the specialization process are not accounted for.
The Resulting ProfileProto will have from_startup set to true in the corresponding ProcessHeapSamples message. This does not get surfaced in the converted pprof compatible proto.
When a profile session is started, all matching processes (by name or PID) are enumerated and profiling is enabled. The resulting profile will contain all allocations done between the beginning and the end of the profiling session.
The Resulting ProfileProto will have from_startup set to false in the corresponding ProcessHeapSamples message. This does not get surfaced in the converted pprof compatible proto.
If multiple sessions name the same target process (either by name or PID), only the first relevant session will profile the process. The other sessions will report that the process had already been profiled when converting to the pprof compatible proto.
If you see this message but do not expect any other sessions, run
adb shell killall -KILL perfetto
to stop any concurrent sessions that may be running.
The Resulting ProfileProto will have rejected_concurrent set to true in otherwise empty corresponding ProcessHeapSamples message. This does not get surfaced in the converted pprof compatible proto.
Depending on the build of Android that heapprofd is run on, some processes are not be eligible to be profiled.
On user builds, only Java applications with either the profileable or the debugable manifest flag set can be profiled. Profiling requests for other processes will result in an empty profile.
On userdebug builds, all processes except for a small blacklist of critical services can be profiled. This restriction can be lifted by disabling SELinux by running adb shell su root setenforce 0 or by passing --disable-selinux to the heap_profile script.
| userdebug setenforce 0 | userdebug | user | |
|---|---|---|---|
| critical native service | y | n | n |
| native service | y | y | n |
| app | y | y | n |
| profileable app | y | y | y |
| debugable app | y | y | y |
If the rate of allocations is too high for heapprofd to keep up, the profiling session will end early due to a buffer overrun. If the buffer overrun is caused by a transient spike in allocations, increasing the shared memory buffer size (passing --shmem-size to heap_profile) can resolve the issue. Otherwise the sampling interval can be increased (at the expense of lower accuracy in the resulting profile) by passing --interval to heap_profile.
Check whether your target process is eligible to be profiled by consulting Target processes above.
When using heapprofd and interpreting results, it is important to know the precise meaning of the different memory metrics that can be obtained from the operating system.
heapprofd gives you the number of bytes the target program requested from the allocator. If you are profiling a Java app from startup, allocations that happen early in the application's initialization will not be visibile to heapprofd. Native services that do not fork from the Zygote are not affected by this.
malloc_info is a libc function that gives you information about the allocator. This can be triggered on userdebug builds by using am dumpheap -m <PID> /data/local/tmp/heap.txt. This will in general be more than the memory seen by heapprofd, depending on the allocator not all memory is immediately freed. In particular, jemalloc retains some freed memory in thread caches.
Heap RSS is the amount of memory requested from the operating system by the allocator. This is larger than the previous two numbers because memory can only be obtained in page size chunks, and fragmentation causes some of that memory to be wasted. This can be obtained by running adb shell dumpsys meminfo <PID> and looking at the “Private Dirty” column.
| heapprofd | malloc_info | RSS | |
|---|---|---|---|
| from native startup | x | x | x |
| after zygote init | x | x | x |
| before zygote init | x | x | |
| thread caches | x | x | |
| fragmentation | x |
If you observe high RSS or malloc_info metrics but heapprofd does not match, there might be a problem with fragmentation or the allocator.
It is not recommended to use these instructions unless you have advanced requirements or are developing heapprofd. Proceed with caution
Download the latest trace_to_text for Linux or MacOS. This is needed to convert the Perfetto trace to a pprof-compatible file.
Compare the sha1sum of this file to the one contained in the file name.
To start profiling the process ${PID}, run the following sequence of commands. Adjust the INTERVAL to trade-off runtime impact for higher accuracy of the results. If INTERVAL=1, every allocation is sampled for maximum accuracy. Otherwise, a sample is taken every INTERVAL bytes on average.
INTERVAL=4096 echo ' buffers { size_kb: 100024 } data_sources { config { name: "android.heapprofd" target_buffer: 0 heapprofd_config { sampling_interval_bytes: '${INTERVAL}' pid: '${PID}' } } } duration_ms: 20000 ' | adb shell perfetto --txt -c - -o /data/misc/perfetto-traces/profile adb pull /data/misc/perfetto-traces/profile /tmp/profile
While we work on UI support, you can convert the trace into pprof compatible heap dumps.
Use the trace_to_text file downloaded above, with XXXXXXX replaced with the sha1sum of the file.
trace_to_text-linux-XXXXXXX profile /tmp/profile
This will create a directory in /tmp/ containing the heap dumps. Run
gzip /tmp/heap_profile-XXXXXX/*.pb
to get gzipped protos, which tools handling pprof profile protos expect.
Follow the instructions in Viewing the Data to visualise the results.