Re: New memory exhausted problem

[John Swensen]

John W. Eaton wrote:
> On 13-Aug-2007, address@hidden wrote:
>
> | I recently have run into a repeatable memory exhausted problem.  I am
> | using Fedora Core 5 with the 2.9.9 version distributed iwht FC5.
> | GNU Octave, version 2.9.9 (i686-redhat-linux-gnu).
> | 
> | The following is the sequence of commands that causes the error:
> | octave:1> a = zeros(640,210,1800); octave:2> b = zeros(640,210,1800);
> | error: memory exhausted -- trying to return to prompt
> | octave:2>
> | 
> | While octave was still running, I ran the 'free' command in a different
> | window.
> | address@hidden Tools]$ free
> |             total       used       free     shared    buffers     cached
> | Mem:       3624816    1338440    2286376          0     157252     957628
> | -/+ buffers/cache:     223560    3401256
> | Swap:      4096564          0    4096564
> | 
> | 
> | Clearly I still have over 2GB of free RAM and the swap disk hasn't even
> | been touched.  Any suggestions as to what is causing the problem?
>
> You are requesting a single allocation of approximately 1.8GB and you
> only have about 2GB free.  I'm not sure of the details of the memory
> management system in the linux kernel, but could it be that it fails
> because although you have enough total space available, there is no
> contiguous block of memory available that is large enough?  Maybe
> someone who knows more about how the allocator is supposed to work
> could give us a clue here.
>
> jwe
>
>   
It ends up that that must be the problem.  I figured that it would at 
least go to the swap disk, yet still permit the allocations, but that 
isn't the case.  It was *not* a limitation on the size of an allocation, 
because we tested allocation of a 3.5 GB chunk without any else 
allocated and it seemed to work fine.  So it seems it must be a problem 
with a large allocation when there is little real memory left.

John Swensen