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0.1.0 Aug 3, 2021
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#566 in Memory management

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Used in lib_malloc_freq

MIT license

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Malloc frequency profiler

This malloc frequency profiler helps detect program hotspots that perform a large number of memory allocations. Many small allocations can slow down your application and lead to memory fragmentation. Typical symptoms include seeing malloc at the top of the application's CPU profile, as well as observing that the resident set size (RSS) of the appliciation significantly exceeds the amount of memory it allocates from the heap.

Note: malloc_freq is different from heap profilers like valgrind's massif, which track program's heap usage at any give point in time, in two ways. First, heap profilers ignore short-lived allocations that do not affect the heap size significantly. Second, heap profilers track the amount of allocated memory, whereas malloc_freq focuses on the number of calls to malloc.

malloc_freq can be used to profile programs in Rust or any other compiled language.

Enabling malloc_freq in a Rust program

To enable malloc_freq in a Rust program, configure it as a global allocator instead of std::alloc::System:

use malloc_freq::ProfAllocator;

static GLOBAL: ProfAllocator = ProfAllocator;

fn main() {}

Using malloc_freq via LD_PRELOAD

For programs in other languages, including a mix of Rust, C, etc., use the companion lib_malloc_freq crate, which produces a dynamic library that can be used via LD_PRELOAD to intercept all malloc calls issued by the program:

LD_PRELOAD=libmalloc_freq.so ./my_program

Viewing malloc_freq profiles

Upon successful program termination, malloc_freq stores the malloc profile in the malloc_freq.<pid> directory. The directory will contain a file for each thread in the program. To view the profile, use the mf_print tool from this crate, e.g.:

mf_print --dir malloc_freq.<pid> --threshold 0.2

where the --threshold switch specifies the significance threshold of profile entries in percents (profile entries with fewer than threshold% malloc calls are skipped in the output). mf_print outputs a human-readable profile that lists program callstacks that perform malloc calls, annotated with the number of malloc calls and the total number of bytes allocated by each stack trace.


To install the mf_print executable:

cargo install malloc_freq

To use malloc_freq in your Rust program via the global_allocator attribute, simply include it as a dependency in your Cargo.toml:

malloc_freq = "0.1"

To use malloc_freq via LD_PRELOAD, you will need to download and build this repository:

git clone git@github.com:ryzhyk/malloc_freq.git
cd malloc_freq
cargo build --release --all

Use the compiled target/release/libmalloc_freq.so library with LD_PRELOAD, as described above.


  • Generate profile on abnormal program termination (e.g., panic or SIGKILL).

  • Subsampling for lower overhead. malloc_freq can slow down the target program significantly, as it currently intercepts all malloc calls and records their stack traces int he profile.


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