Re: Memory overcommit misbehaves

"jon wayne" <jon.wayne.01@xxxxxxxxx> writes:

Hi

I was always under the assumption that linux always overcommits memory
by default - but I'm getting unexpected results
while requesting for a large ammount of memory using new (c++).

Linux does not overcommit memory.

In the sense , say I try and allocate dynamically a large array p (int
*p)

p = (int *) malloc(N * sizeof(int)); // ----
1

and replace it by

p = new int[ N * sizeof(int)]; // -- 2

where N = 1000000000000000 //

the second statement always generates a bad_alloc exception ---

I would hope so. Your system does not have that much memory, either in ram
or swap or anything else also 4x10^15=2^52 is probably far more than the
address bus on your system can allocate.
Just why are you trying to do such a rediculous thing?


Agreed that if you try and access p it'd give a SIGSEGV - but why
should a plain allocation give a bad_alloc - "C" doesn't seem to mind
it - shouldn't C++ too??

I suspect it could be because C++ uses a different memory management
library - could someone please clarify.

(When I do an strace - I find both of the above versions end up
calling mmap().)

Maybe if you told us what it is that you really want to do, rather than
this totally made up example, you might get better help.


ENV -

gcc 3.4.3

linux - 2.4.21-40.EL

I'd really appreciate some info on this,

Regards
Aditya

.

Relevant Pages

  • Linux ELF loader vulnerabilities
    ... Numerous bugs have been found in the Linux ELF binary loader while ... Internally the Linux kernel uses a binary format loader layer to ... and the position of the memory map header in the binary image and ... An user may try to execute such a malicious binary with an unterminated ...
    (Bugtraq)
  • [Full-Disclosure] Linux ELF loader vulnerabilities
    ... Numerous bugs have been found in the Linux ELF binary loader while ... Internally the Linux kernel uses a binary format loader layer to ... and the position of the memory map header in the binary image and ... An user may try to execute such a malicious binary with an unterminated ...
    (Full-Disclosure)
  • Linux ELF loader vulnerabilities
    ... Numerous bugs have been found in the Linux ELF binary loader while ... Internally the Linux kernel uses a binary format loader layer to ... and the position of the memory map header in the binary image and ... An user may try to execute such a malicious binary with an unterminated ...
    (Full-Disclosure)
  • Re: How to set up a Linux machine that occupies the minimum memory footprint ?
    ... Of course, if you use 8GB of RAM, or more precisely if you ... Are you saying that if I have a 4GB RAM memory, ... Linux will somehow "know" that it doesn't have ... You've said in another message that your app is ...
    (comp.os.linux.setup)
  • Re: How to set up a Linux machine that occupies the minimum memory footprint ?
    ... Of course, if you use 8GB of RAM, or more precisely if you ... Are you saying that if I have a 4GB RAM memory, ... Linux will somehow "know" that it doesn't have ... You've said in another message that your app is ...
    (comp.os.linux.misc)