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

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

Rik van Riel wrote:
> On Tue, 25 Nov 2003, Ihar 'Philips' Filipau wrote:
> 
>> 2.6: the same as 2.4 with oom killer (default conf). I have no test
>>  system to check 2.6. w/o oom killer.
> 
> 
> # echo 2 > /proc/sys/vm/overcommit_memory
> 
> Then try again.
> 

   What do you know what is not said in docs?
   What '2' means?

   I'll try as soon as I will have again access to 2.6 box.

   this is what 2.6-test10 says:

> overcommit_memory
> 
> This file  contains  one  value.  The following algorithm is used to
> decide if there's enough  memory:  if  the  value of
> overcommit_memory is positive, then there's always  enough  memory.
> This is a useful feature, since programs often malloc() huge  amounts
> of  memory 'just in case', while they only use a small part of  it.
> Leaving  this value at 0 will lead to the failure of such a huge 
> malloc(), when in fact the system has enough memory for the program
> to run.
> 
> On the  other  hand,  enabling this feature can cause you to run out
> of memory and thrash the system to death, so large and/or important
> servers will want to set this value to 0.

   Could this special case 'sysctl_overcommit_memory > 1' be added and 
explained? (mmap.c:589)

   I cannot tell what it does - but name 'security_vm_enough_memory()' 
sounds promising ;-)

   As I have said - I will check this later when I will get to those box.

-- 
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