Re: 2.2/2.4/2.6 VMs: do malloc() ever return NULL?

["Ihar 'Philips' Filipau" <filia@softhome.net>]

Arjan van de Ven wrote:
> 
> that is due to the overcommit policy that your admin has set. 
> You can set it to disabled and then malloc will return NULL in userspace
> 

    Target (patched by mvista) system works as expected in case of 
memory being touch.
    But in case of "for(;;) malloc(N)" it still gets 1.8GB memory 
allocated. (this is ppc32 - looks like 2/2 memory split) So it doesn't 
look like working at all. So basicly pool allocation used in carrier 
grade systems goes south: even with overcommit_memory=-1 && malloc()!=0 
you can not be sure that memory is really allocated. Not good.

    Vanilla 2.4.22 (this is x86) (with HZ=1024, if it does matter).

    after '# echo -1 >/proc/sys/vm/overcommit_memory'
    1. test app with memory touch still gets killed by oom_killer. (so 
no malloc() == NULL)
    2. test app w/o memory touch still can happily allocate 2.8GB of 
memory (x86 - looks like 3/1 memory split) and only then gets NULL 
pointer - oom_killer is silent.

    But thanks for pointers in any way...

-- 
Ihar 'Philips' Filipau  / with best regards from Saarbruecken.
--                                                           _ _ _
  Because the kernel depends on it existing. "init"          |_|*|_|
  literally _is_ special from a kernel standpoint,           |_|_|*|
  because its' the "reaper of zombies" (and, may I add,      |*|*|*|
  that would be a great name for a rock band).
                                 -- Linus Torvalds