heap limits: mmap(2) vs. break(2) on i386

[Andrew MacIntyre]

Maxim Sobolev wrote:
> Jason Evans wrote:

>> I would set MAXDSIZ to 0, so that the maximum amount of memory is 
>> available for mapping shared libraries and files, and allocating via 
>> malloc.  This may cause problems with a couple of ports that implement 
>> their own memory allocators based on sbrk, but otherwise it should be 
>> all good.  You might also set /etc/malloc.conf  to 'd' in order to 
>> disable the sbrk calls.
> 
> I see, thank you for the explanation. One of the problem that we are 
> having is that we use a lot of interpreted languages in our environment 
> (python, php etc), and most of those implement their own memory 
> allocators, some of which rely on sbrk(2) unfortunately. I believe 
> that's where that 2GB limit of ours comes from - one of our Python 
> applications is very memory hungry and we had to bump that limit to 
> allow it sufficient room.

While Python has its own allocator, it relies on the platform malloc()
rather than sbrk(), and therefore Jason's suggestion to use '-d' in
/etc/malloc.conf should be effective for it.

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