Kernel Not Able to Regain Deallocated Memory

[Kedar Pimplikar]

Hello All,

I have a process, which makes use of recursive function,
and in each call, allocates lot of memory on stack.

When I run this process on Redhat Linux AS 3.0 (IA-32),
(Kernel:2.4.21-4.EL) it has a little strange behavior.

Free Memory before running my process: @ 380 MB
Free Memory after running my process: @ 80 MB

I am sure that my application does not consume this huge memory. (@300 MB)
It allocates a very little memory @ 8 KB dynamically, which it frees
correctly.
My application does not have any memory leaks.
I have confirmed it through code-review and rational purify.

My doubts are:
1. Is this behavior of kernel is actually a feature (and not a bug) or
kernel is unable to recover memory deallocted by a process.
(If yes, please let me know if is documented)

2. Are bdflush parameters responsible for this behavior?
My current bdflush parameters are as
#cat /proc/sys/vm/bdflush
50      500     0       0       500     3000    80      50      0

I tried manipulating these values but no improvement seen.

I also tried to process behavior as follows:
Instead allocating huge memory on stack, I allocate it dynamically on heap.
This way I can ensure the freeing up of memory.
But still result is same.

One more interesting observation:
After running my application once, (kernel has @ 80 MB free memory)
I rerun my application but this time there is no drop in free memory.

Any input in this regard will really help me.

(Thanks anyway for reading this far...)


Regards,
Kedar.



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