From: Yohanes Santoso <ysantoso-rubytalk@...>
Date: 2007-10-19T17:28:46+09:00
Subject: Re: [OT] Re: Should *most* memory be release back to the system?

MenTaLguY <mental@rydia.net> writes:

> On Fri, 19 Oct 2007 04:13:58 +0900, Joel VanderWerf <vjoel@path.berkeley.edu> wrote:
>> Yohanes Santoso wrote:
>>>   mallopt(M_MMAP_THRESHOLD, 0); /* declared in malloc.h */
>> 
>> Very interesting. I'd like to use this as a diagnostic.
>> 
>> I patched ruby's main.c to call mallopt() before anything else. It seems
>> to be using a huge amount of memory, though. Is this normal?
>
> Using mmap for individual allocations means that each allocation
> gets rounded up to the nearest multiple of the page size
> (typically 4k).
>
> That aside, I'm not sure it's that useful as a diagnostic; note
> that only M_MMAP_MAX chunks will ever be allocated at a time with
> mmap; further allocations beyond that are allocated the normal way
> by advancing sbrk.
>
> -mental

I suppose all these could be offered as an extension module. At the
very least allow: Malloc.m_mmap_threshold=(),m_mmap_max=(), and
stat() which returns wrapped struct mallinfo.[1] This is so you don't
have to pay for allocations not done by your app like allocations
internal to ruby and/or RoR.

From struct mallinfo, it seems you can get the actual memory use with
hblkhd + uordblks which would provide yet another way to diagnose the
raising VSZ problem. Perhaps mental can confirm this? 


YS.


Footnotes: 
[1]  http://www.gnu.org/software/libc/manual/html_node/Statistics-of-Malloc.html#Statistics-of-Malloc