UNIX for Dummies Questions & Answers

Hi All,

In my application malloc is returning NULL even though there is sufficient amount of free memory available but the swap memory is low.

Is this possible that, if free memory is high & swap memory is low, malloc will not be able to allocate memory & return NULL ?


Few details:

my system running on a x86 platform
2 Pentium III processors
MPRAS version 3.03
output of OS level and current kernel patch level 03.03.02.15

Commands I used to measure free memory and swap :

[ app001-0 root:/ ] sar -r 1 10

app001-0 app001-0 4.2 3.3 SDS2 06/03/08

06:56:32 freemem freeswp
06:56:33 513222 10197
06:56:34 513205 10197
06:56:35 513210 10197
06:56:36 513210 10197
06:56:37 513231 10197
06:56:38 513271 10197
06:56:39 513271 10197
06:56:40 513268 10197
06:56:41 513258 10197
06:56:42 513258 10197
Kindly look into the issue as I am not able to start my application in the above mentioned condition.

Thanks & Regards,
Ritesh

Hi All,

Please look into the problem mentioned above as this very important for me to know the answer.

Regards n Thanks,
Ritesh

How much are you trying to allocate? How much can you allocate before you hit the error?

I have never heard of MPRAS before. But most versions of unix used to work exactly as you describe. If you have 16 megs of memory, you needed 16 megs of swap just to be able to use all of the memory. When memory sizes were small it wasn't a big deal to effectively waste 16 megs of swap. The idea was that you never allocated in-core memory until you knew where to swap it to. And the rule of thumb was that your swap area should be 3 times your memory size. It could be that your version of unix still works this way. How old is this MPRAS?

Thanks All for your kind help.