Native heap profiler

NOTE: heapprofd requires Android 10 or higher

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 call-stacks, supporting a mix of both native and java code. The tool can be used by Android platform and app developers to investigate 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.

Quickstart

See the Memory Guide for getting started with heapprofd.

UI

Dumps from heapprofd are shown as flamegraphs in the UI after clicking on the diamond. Each diamond corresponds to a snapshot of the allocations and callstacks collected at that point in time.

heapprofd snapshots in the UI tracks

heapprofd flamegraph

SQL

Information about callstacks is written to the following tables:

The allocations themselves are written to heap_profile_allocation.

Offline symbolization data is stored in stack_profile_symbol.

See Example Queries for example SQL queries.

Recording

Heapprofd can be configured and started in three ways.

Manual configuration

This requires manually setting the HeapprofdConfig section of the trace config. The only benefit of doing so is that in this way heap profiling can be enabled alongside any other tracing data sources.

Using the tools/heap_profile script (recommended)

On Linux / MacOS, use the tools/heap_profile script. If you are having trouble make sure you are using the latest version.

You can target processes either by name (-n com.example.myapp) or by PID (-p 1234). In the first case, the heap profile will be initiated on both on already-running processes that match the package name and new processes launched after the profiling session is started. For the full arguments list see the heap_profile cmdline reference page.

Using the Recording page of Perfetto UI

You can also use the Perfetto UI to record heapprofd profiles. Tick "Heap profiling" in the trace configuration, enter the processes you want to target, click "Add Device" to pair your phone, and record profiles straight from your browser. This is also possible on Windows.

Viewing the data

The resulting profile proto contains four views on the data

(Googlers: You can also open the gzipped protos using http://pprof/)

TIP: you might want to put libart.so as a "Hide regex" when profiling apps.

You can use the Perfetto UI to visualize heap dumps. Upload the raw-trace file in your output directory. You will see all heap dumps as diamonds on the timeline, click any of them to get a flamegraph.

Alternatively Speedscope can be used to visualize the gzipped protos, but will only show the space view.

TIP: Click Left Heavy on the top left for a good visualization.

Sampling interval

Heapprofd samples heap allocations by hooking calls to malloc/free and C++'s operator new/delete. 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 stream of one byte allocations. From this stream, every byte has a 1/n probability of being selected as a sample, and the corresponding callstack gets attributed the complete n bytes. For more accuracy, allocations larger than the sampling interval bypass the sampling logic and are recorded with their true size.

Startup profiling

When specifying a target process name (as opposite to the PID), new processes matching that name are profiled from their startup. 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 exec()-ed from scratch, but fork()-ed from the zygote, which 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.

At the trace proto level, the resulting ProfilePacket will have the from_startup field set to true in the corresponding ProcessHeapSamples message. This is not surfaced in the converted pprof compatible proto.

Runtime profiling

When a profiling 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 ProfilePacket will have from_startup set to false in the corresponding ProcessHeapSamples message. This does not get surfaced in the converted pprof compatible proto.

Concurrent profiling sessions

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 perfetto

to stop any concurrent sessions that may be running.

The resulting ProfilePacket will have rejected_concurrent set to true in otherwise empty corresponding ProcessHeapSamples message. This does not get surfaced in the converted pprof compatible proto.

Target processes

Depending on the build of Android that heapprofd is run on, some processes are not be eligible to be profiled.

On user (i.e. production, non-rootable) builds, only Java applications with either the profileable or the debuggable manifest flag set can be profiled. Profiling requests for non-profileable/debuggable processes will result in an empty profile.

On userdebug builds, all processes except for a small blacklist of critical services can be profiled (to find the blacklist, look for never_profile_heap in heapprofd.te. 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
debuggable app Y Y Y

To mark an app as profileable, put <profileable android:shell="true"/> into the <application> section of the app manifest.

<manifest ...> <application> <profileable android:shell="true"/> ... </application> </manifest>

DEDUPED frames

If the name of a Java method includes [DEDUPED], this means that multiple methods share the same code. ART only stores the name of a single one in its metadata, which is displayed here. This is not necessarily the one that was called.

Triggering heap snapshots on demand

Heap snapshot are recorded into the trace either at regular time intervals, if using the continuous_dump_config field, or at the end of the session.

You can also trigger a snapshot of all currently profiled processes by running adb shell killall -USR1 heapprofd. This can be useful in lab tests for recording the current memory usage of the target in a specific state.

This dump will show up in addition to the dump at the end of the profile that is always produced. You can create multiple of these dumps, and they will be enumerated in the output directory.

Symbolization

NOTE: Symbolization is currently only available on Linux

Set up llvm-symbolizer

You only need to do this once.

To use symbolization, your system must have llvm-symbolizer installed and accessible from $PATH as llvm-symbolizer. On Debian, you can install it using sudo apt install llvm-9. This will create /usr/bin/llvm-symbolizer-9. Symlink that to somewhere in your $PATH as llvm-symbolizer.

For instance, ln -s /usr/bin/llvm-symbolizer-9 ~/bin/llvm-symbolizer, and add ~/bin to your path (or run the commands below with PATH=~/bin:$PATH prefixed).

Symbolize your profile

If the profiled binary or libraries do not have symbol names, you can symbolize profiles offline. Even if they do, you might want to symbolize in order to get inlined function and line number information. All tools (traceconv, trace_processor_shell, the heap_profile script) support specifying the PERFETTO_BINARY_PATH as an environment variable.

PERFETTO_BINARY_PATH=somedir tools/heap_profile --name ${NAME}

You can persist symbols for a trace by running PERFETTO_BINARY_PATH=somedir tools/traceconv symbolize raw-trace > symbols. You can then concatenate the symbols to the trace ( cat raw-trace symbols > symbolized-trace) and the symbols will part of symbolized-trace. The tools/heap_profile script will also generate this file in your output directory, if PERFETTO_BINARY_PATH is used.

The symbol file is the first with matching Build ID in the following order:

  1. absolute path of library file relative to binary path.
  2. absolute path of library file relative to binary path, but with base.apk! removed from filename.
  3. basename of library file relative to binary path.
  4. basename of library file relative to binary path, but with base.apk! removed from filename.
  5. in the subdirectory .build-id: the first two hex digits of the build-id as subdirectory, then the rest of the hex digits, with ".debug"appended. See https://fedoraproject.org/wiki/RolandMcGrath/BuildID#Find_files_by_build_ID

For example, "/system/lib/base.apk!foo.so" with build id abcd1234, is looked for at:

  1. $PERFETTO_BINARY_PATH/system/lib/base.apk!foo.so
  2. $PERFETTO_BINARY_PATH/system/lib/foo.so
  3. $PERFETTO_BINARY_PATH/base.apk!foo.so
  4. $PERFETTO_BINARY_PATH/foo.so
  5. $PERFETTO_BINARY_PATH/.build-id/ab/cd1234.debug

Troubleshooting

Buffer overrun

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 tools/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=16000 or higher.

Profile is empty

Check whether your target process is eligible to be profiled by consulting Target processes above.

Also check the Known Issues.

Implausible callstacks

If you see a callstack that seems to impossible from looking at the code, make sure no DEDUPED frames are involved.

Also, if your code is linked using Identical Code Folding (ICF), i.e. passing -Wl,--icf=... to the linker, most trivial functions, often constructors and destructors, can be aliased to binary-equivalent operators of completely unrelated classes.

Symbolization: Could not find library

When symbolizing a profile, you might come across messages like this:

Could not find /data/app/invalid.app-wFgo3GRaod02wSvPZQ==/lib/arm64/somelib.so (Build ID: 44b7138abd5957b8d0a56ce86216d478).

Check whether your library (in this example somelib.so) exists in PERFETTO_BINARY_PATH. Then compare the Build ID to the one in your symbol file, which you can get by running readelf -n /path/in/binary/path/somelib.so. If it does not match, the symbolized file has a different version than the one on device, and cannot be used for symbolization. If it does, try moving somelib.so to the root of PERFETTO_BINARY_PATH and try again.

Only one frame shown

If you only see a single frame for functions in a specific library, make sure that the library has unwind information. We need one of

Frame-pointer unwinding is not supported.

To check if an ELF file has any of those, run

$ readelf -S file.so | grep "gnu_debugdata\|eh_frame\|debug_frame" [12] .eh_frame_hdr PROGBITS 000000000000c2b0 0000c2b0 [13] .eh_frame PROGBITS 0000000000011000 00011000 [24] .gnu_debugdata PROGBITS 0000000000000000 000f7292

If this does not show one or more of the sections, change your build system to not strip them.

Known Issues

Android 10

Heapprofd vs malloc_info() vs RSS

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 default C/C++ allocator. If you are profiling a Java app from startup, allocations that happen early in the application's initialization will not be visible 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. RSS can also end up being smaller than the other two if the device kernel uses memory compression (ZRAM, enabled by default on recent versions of android) and the memory of the process get swapped out onto ZRAM.

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, you might be hitting some patological fragmentation problem in the allocator.

Convert to pprof

You can use traceconv to convert the heap dumps in a trace into the pprof format. These can then be viewed using the pprof CLI or a UI (e.g. Speedscope, or Google-internal pprof/).

tools/traceconv 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.

Example SQL Queries

We can get the callstacks that allocated using an SQL Query in the Trace Processor. For each frame, we get one row for the number of allocated bytes, where count and size is positive, and, if any of them were already freed, another line with negative count and size. The sum of those gets us the space view.

select a.callsite_id, a.ts, a.upid, f.name, f.rel_pc, m.build_id, m.name as mapping_name, sum(a.size) as space_size, sum(a.count) as space_count from heap_profile_allocation a join stack_profile_callsite c ON (a.callsite_id = c.id) join stack_profile_frame f ON (c.frame_id = f.id) join stack_profile_mapping m ON (f.mapping = m.id) group by 1, 2, 3, 4, 5, 6, 7 order by space_size desc;
callsite_id ts upid name rel_pc build_id mapping_name space_size space_count
6660 5 1 malloc 244716 8126fd.. /apex/com.android.runtime/lib64/bionic/libc.so 106496 4
192 5 1 malloc 244716 8126fd.. /apex/com.android.runtime/lib64/bionic/libc.so 26624 1
1421 5 1 malloc 244716 8126fd.. /apex/com.android.runtime/lib64/bionic/libc.so 26624 1
1537 5 1 malloc 244716 8126fd.. /apex/com.android.runtime/lib64/bionic/libc.so 26624 1
8843 5 1 malloc 244716 8126fd.. /apex/com.android.runtime/lib64/bionic/libc.so 26424 1
8618 5 1 malloc 244716 8126fd.. /apex/com.android.runtime/lib64/bionic/libc.so 24576 4
3750 5 1 malloc 244716 8126fd.. /apex/com.android.runtime/lib64/bionic/libc.so 12288 1
2820 5 1 malloc 244716 8126fd.. /apex/com.android.runtime/lib64/bionic/libc.so 8192 2
3788 5 1 malloc 244716 8126fd.. /apex/com.android.runtime/lib64/bionic/libc.so 8192 2

We can see all the functions are "malloc" and "realloc", which is not terribly informative. Usually we are interested in the cumulative bytes allocated in a function (otherwise, we will always only see malloc / realloc). Chasing the parent_id of a callsite (not shown in this table) recursively is very hard in SQL.

There is an experimental table that surfaces this information. The API is subject to change.

select name, map_name, cumulative_size from experimental_flamegraph(8300973884377,1,'native') order by abs(cumulative_size) desc;
name map_name cumulative_size
__start_thread /apex/com.android.runtime/lib64/bionic/libc.so 392608
_ZL15__pthread_startPv /apex/com.android.runtime/lib64/bionic/libc.so 392608
_ZN13thread_data_t10trampolineEPKS /system/lib64/libutils.so 199496
_ZN7android14AndroidRuntime15javaThreadShellEPv /system/lib64/libandroid_runtime.so 199496
_ZN7android6Thread11_threadLoopEPv /system/lib64/libutils.so 199496
_ZN3art6Thread14CreateCallbackEPv /apex/com.android.art/lib64/libart.so 193112
_ZN3art35InvokeVirtualOrInterface... /apex/com.android.art/lib64/libart.so 193112
_ZN3art9ArtMethod6InvokeEPNS_6ThreadEPjjPNS_6JValueEPKc /apex/com.android.art/lib64/libart.so 193112
art_quick_invoke_stub /apex/com.android.art/lib64/libart.so 193112