[mercury-users] Debugging 'memory leaks' (fwd)

[Ondrej Bojar]

Peter Wang wrote:
>> but the heapsize never sinks, as show in the truncated log below.
> 
> That's the normal behaviour without munmap, so unless the heap seems to
> keep growing without bound, I wouldn't worry about it.

I've investigated the issue with rotd-2008-03-27 and --boehm-gc-munmap, 
and nothing is unmapped even in this case.

When checking memory usage using GC_get_heap_size a GC_get_free_bytes, I 
can confirm that there is no leak as such. The estimated number of free 
bytes grows significantly at expected places. The issue is heap size.

Unfortunately I have to worry about the heap size, because I run the 
task on many machines with other users and other processes... I can 
afford peaks in memusage from time to time, but I need to free it back 
for others.

I have two guesses what needs a fix:

1. ./boehm_gc/os_dep.c: GC_unix_get_mem
    When allocating memory, GC_unix_get_mem first try to do it using 
sbrk. I have never allocated memory this way so I'm just guessing that 
one cannot simply make holes in a process data segment by dealocating 
bits of it. My guess is that GC_unix_mmap_get_mem should be preferred 
with --boehm-gc-munmap

2. ./boehm_gc/allchblk.c: GC_freehblk
     There is a FIXME remark at the end of the function that indicates a 
problem with timestamps => no block would become old enough to munmap.

Before I delve deeper to figure out which of 1. and/or 2. indeed hold in 
my case and try to tweak them without knowing much about the GC, I'd 
like to hear your opinion. Can you rule out something right away?

Thanks, Ondrej.

> 
>> I will try using --boehm-gc-munmap as soon as I get a recent ROTD compiled.
>>
>> Thanks!
>>   Ondrej.
> 
> Peter
> 
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-- 
Ondrej Bojar (mailto:obo at cuni.cz / bojar at ufal.mff.cuni.cz)
http://www.cuni.cz/~obo
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