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

[Ihar 'Philips' Filipau]

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

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