Q31559 Allocating More Than 4 Megabytes, Loss of Speed after 32K
C Compiler
5.10   | 5.10
MS-DOS | OS/2

Question:
   I have written a program in C that allocates memory in 32K pieces
to see how much memory is available to my program. Malloc returns a
null at about 4 megabytes. I thought that I had access to 1 gigabyte
of memory with OS/2. Is there a limitation that I do not know about
with malloc in OS/2? Also, the system slows down extremely after the
first 32K gets allocated. What causes that?

Response:
   Under C Version 5.10, malloc is limited to 64 segment-resource
pools, which means malloc can only allocate 4 megabytes of memory
under OS/2. This limitation is a constant in the malloc run-time
routine and can be raised by modifying the library source code.
   The speed degradation is caused by malloc scanning the segments for
a block of free memory, most of which has been swapped to disk;
therefore, performance degradation ("thrashing") occurs as the memory
is swapped in and out from disk.
   Microsoft has confirmed this to be a problem in Version 5.10 of the
C compiler.
   We are researching this problem and will post new information as it
becomes available.

Keywords:  buglist5.10
Updated  88/07/21 03:19