[Mono-dev] Leaky JIT while running MonoDevelop

[Casey Marshall]

I've been seeing a memory leak -- or, maybe instead, "unbounded memory 
growth" -- while running MonoDevelop (SVN code of MD, mono-2-0 SVN of 
Mono). I've been running it under valgrind, and after running it 
overnight, I find traces like this in the output:

> ==7947== 862,223,392 bytes in 1,737,838 blocks are still reachable in loss record 238 of 238
> ==7947==    at 0x4C21F8F: memalign (vg_replace_malloc.c:460)
> ==7947==    by 0x4C22028: posix_memalign (vg_replace_malloc.c:569)
> ==7947==    by 0x507D299: (within /usr/lib/libglib-2.0.so.0.1600.4)
> ==7947==    by 0x507E0F0: g_slice_alloc (in /usr/lib/libglib-2.0.so.0.1600.4)
> ==7947==    by 0x506035D: g_list_prepend (in /usr/lib/libglib-2.0.so.0.1600.4)
> ==7947==    by 0x432953: mono_arch_get_allocatable_int_vars (mini-amd64.c:910)
> ==7947==    by 0x5579A9: mini_method_compile (mini.c:12490)
> ==7947==    by 0x558CF8: mono_jit_compile_method (mini.c:12819)
> ==7947==    by 0x42C5A2: mono_magic_trampoline (mini-trampolines.c:249)
> ==7947==    by 0x415B164: ???
> ==7947==    by 0x8FCA917: ???
> ==7947==    by 0x85E7E9F: ???

(there are many other traces, but they're all two orders of magnitude 
smaller, in terms of memory size)

I ran the same test again, this time with --optimize=-linears (which is 
where at least the above trace came from) and without --debug, and 
memory still grew, but not quite as quickly. I got another valgrind 
trace out of that run:

> ==5807== 794,797,632 bytes in 1,601,948 blocks are still reachable in loss record 238 of 238
> ==5807==    at 0x4C21F8F: memalign (vg_replace_malloc.c:460)
> ==5807==    by 0x4C22028: posix_memalign (vg_replace_malloc.c:569)
> ==5807==    by 0x507D299: (within /usr/lib/libglib-2.0.so.0.1600.4)
> ==5807==    by 0x507E0F0: g_slice_alloc (in /usr/lib/libglib-2.0.so.0.1600.4)
> ==5807==    by 0x506035D: g_list_prepend (in /usr/lib/libglib-2.0.so.0.1600.4)
> ==5807==    by 0x52AF25: mono_allocate_stack_slots_full (mini.c:9812)
> ==5807==    by 0x432320: mono_arch_allocate_vars (mini-amd64.c:1137)
> ==5807==    by 0x558127: mini_method_compile (mini.c:12525)
> ==5807==    by 0x559419: mono_jit_compile_method (mini.c:12836)
> ==5807==    by 0x42C5E2: mono_magic_trampoline (mini-trampolines.c:249)
> ==5807==    by 0x415B164: ???
> ==5807==    by 0x8BA4AAB: ???

I think valgrind just didn't capture this one the first time, but it was 
a factor in the memory growth.

I suppose that because MonoDevelop uses a fair amount of dynamic code, 
it uses the JIT a lot, which seems to be provoking this. I personally 
can't figure out why this memory is still reachable -- these are all 
GLists, and it looks like they are passed to g_list_free at the end. I 
suppose either some nodes are being lost after sorting, or something 
more subtle is going on.

This is glib version 2.16.4-0ubuntu2, on Ubuntu 8.04, amd64.

Thanks.