Hello Guilers,

While desperately chasing <https://issues.guix.gnu.org/59021> and
related memory leak issues, I came up with the attached rudimentary heap
profiler.  You can load it and invoking it in a running process:

--8<---------------cut here---------------start------------->8---
scheme@(guile-user)> (profile-heap)
  %   type                               self    avg obj size
 19.7 pair                                  720,864    16.0
 16.3 unknown                               594,832   600.8
 14.7 struct                                536,784    48.2
 12.6 bytevector                            461,824  1110.2
  7.7 stringbuf                             281,136   117.8
  6.8 pointer                               248,688    16.0
  5.5 vector                                202,815    35.4
  4.1 symbol                                148,640    32.0
  3.1 program                               113,824    40.0
  1.6 heap-number                            59,680    31.8
  1.5 string                                 54,960    32.0
  1.4 smob                                   52,736    38.0
  1.3 variable                               49,328    22.6
  0.8 weak-table                             30,144    30.4
  0.8 atomic-box                             28,528    32.1
  0.8 vm-continuation                        27,680    32.0
  0.7 hash-table                             26,736    32.1
  0.2 syntax                                  6,144    48.0
  0.1 dynamic-state                           4,208  1052.0
  0.1 primitive                               2,880    16.0
  0.1 weak-vector                             1,984    18.0
  0.0 keyword                                   752    16.7
  0.0 bitvector                                 672    35.4
  0.0 frame                                     624    39.0
  0.0 primitive-generic                         608    32.0
  0.0 continuation                              576   576.0
  0.0 fluid                                     208    29.7
  0.0 array                                      96    48.0
  0.0 weak-set                                   96    48.0
  0.0 port                                       64    32.0
sampled heap: 3.48865 MiB (heap size: 12.78906 MiB)
$5 = #t
--8<---------------cut here---------------end--------------->8---

It samples the GC-managed heap and counts the number and size of objects
of each type.  The “unknown” bit is anything that lacks a type tag, such
as stacks allocated for delimited continuations by ‘capture_stack’ in
libguile.

It gives a rough idea of what’s going on but of course it’s intrusive:
the profiling process itself allocates memory.  The next step will be to
run it from GDB so that it’s non-intrusive.

I’d be curious to know if people have developed similar tools in this
area.

Ludo’.