# 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](/docs/case-studies/memory.md#heapprofd) 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](/docs/images/profile-diamond.png)

![heapprofd flamegraph](/docs/images/native-flamegraph.png)

## SQL

Information about callstacks is written to the following tables:

* [`stack_profile_mapping`](/docs/analysis/sql-tables.autogen#stack_profile_mapping)
* [`stack_profile_frame`](/docs/analysis/sql-tables.autogen#stack_profile_frame)
* [`stack_profile_callsite`](/docs/analysis/sql-tables.autogen#stack_profile_callsite)

The allocations themselves are written to
[`heap_profile_allocation`](/docs/analysis/sql-tables.autogen#heap_profile_allocation).

Offline symbolization data is stored in
[`stack_profile_symbol`](/docs/analysis/sql-tables.autogen#stack_profile_symbol).

See [Example Queries](#heapprofd-example-queries) for example SQL queries.

## Recording

Heapprofd can be configured and started in three ways.

#### Manual configuration

This requires manually setting the
[HeapprofdConfig](/docs/reference/trace-config-proto.autogen#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](
https://raw.githubusercontent.com/google/perfetto/master/tools/heap_profile).

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](/docs/reference/heap_profile-cli).

#### Using the Recording page of Perfetto UI

You can also use the [Perfetto UI](https://ui.perfetto.dev/#!/record?p=memory)
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

* **space**: how many bytes were allocated but not freed at this callstack the
  moment the dump was created.
* **alloc\_space**: how many bytes were allocated (including ones freed at the
  moment of the dump) at this callstack
* **objects**: how many allocations without matching frees were done at this
  callstack.
* **alloc\_objects**: how many allocations (including ones with matching frees)
  were done at this callstack.

_(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](https://ui.perfetto.dev) 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](https://speedscope.app) 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.

[ProfilePacket]: /docs/reference/trace-packet-proto.autogen#ProfilePacket
[zygote]: https://developer.android.com/topic/performance/memory-overview#SharingRAM

## 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

```shell
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.

## {#heapprofd-targets} 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 set of critical
services can be profiled (to find the set of disallowed targets, look for
`never_profile_heap` in [heapprofd.te](
https://cs.android.com/android/platform/superproject/+/master:system/sepolicy/private/heapprofd.te?q=never_profile_heap).
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.

<center>

|                         | 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   |

</center>

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

```xml
<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 and MacOS.

### 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

Alternatively, you can set the `PERFETTO_SYMBOLIZER_MODE` environment variable
to `index`, and the symbolizer will recursively search the given directory for
an ELF file with the given build id. This way, you will not have to worry
about correct filenames.

## 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](#target-processes) above.

Also check the [Known Issues](#known-issues).

### Implausible callstacks

If you see a callstack that seems to impossible from looking at the code, make
sure no [DEDUPED frames](#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:

```bash
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

* `.gnu_debugdata`
* `.eh_frame` (+ preferably `.eh_frame_hdr`)
* `.debug_frame`.

Frame-pointer unwinding is *not supported*.

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

```console
$ 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

* On ARM32, the bottom-most frame is always `ERROR 2`. This is harmless and
  the callstacks are still complete.
* x86 platforms are not supported. This includes the Android _Cuttlefish_
  emulator.
* If heapprofd is run standalone (by running `heapprofd` in a root shell, rather
  than through init), `/dev/socket/heapprofd` get assigned an incorrect SELinux
  domain. You will not be able to profile any processes unless you disable
  SELinux enforcement.
  Run `restorecon /dev/socket/heapprofd` in a root shell to resolve.
* Using `vfork(2)` or `clone(2)` with `CLONE_VM` and allocating / freeing
  memory in the child process will prematurely end the profile.
  `java.lang.Runtime.exec` does this, calling it will prematurely end
  the profile. Note that this is in violation of the POSIX standard.

## 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](/docs/quickstart/traceconv.md) to convert the heap dumps
in a trace into the [pprof](https://github.com/google/pprof) format. These can
then be viewed using the pprof CLI or a UI (e.g. Speedscope, or Google-internal
pprof/).

```bash
tools/traceconv profile /tmp/profile
```

This will create a directory in `/tmp/` containing the heap dumps. Run:

```bash
gzip /tmp/heap_profile-XXXXXX/*.pb
```

to get gzipped protos, which tools handling pprof profile protos expect.

## {#heapprofd-example-queries} 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.

```sql
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**.

```sql
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|