Memory allocation between RHEL 3.0 and RHEL 4.0 (and 5.2)

[Jerry Feldman]

I got some email from one of my coworkers in Toronto that they were=20
having some memory allocation issues in RHEL4.
The program is a simpleC++ that uses the C++ new operator to allocate a=20
character array:
 new char[chunk];
Where chunk is 10240.  The results shown below are the ones I got from=20
my coworker, but I repeated the test and got similar results.
(I'll send the C++ code if anyone wants to reproduce it.).  The=20
underlying problem is that they are having issues with our product=20
running out of memory on RHEL 4.0 and 5.2. I'd like to be able to=20
explain what the differences are between RHEL 3 (2.4.21 kernel) and RHEL =

4 (2.6.9 kernel).

HOW TO REPRODUCE:

Both systems are Xeons with 4GB.
system1 is RHEL 3.0 Update 1
system2 is RHEL 4.0 Update 5

1) Compile the attached program on a rhel-3 machine.
Compiler is gcc-3.3.3 in both cases, not the installed compiler.
The executable was built on system1 and run on both systems.
A second test where the program was compiled on system2 with the same=20
compiler produced the same results
as the original test on system2. Both systems are 32-bit, both suport=20
pae, and both are single-core multiple processors with 4GB memory.


The compile command was: /<location>/gcc-3.3.3/bin/g++ testMem.C -o testM=
em

Results on system1 (RHEL 3.0)
Allocating: 10240 bytes, 100 times.
proc size at start =3D 790528
proc size at end =3D 1363968: numPages =3D 333
PageSize =3D 4096
proc grew by =3D 573440
total number of pages =3D 140

*Allocating: 1024000 all at once.
* total process grew by: 4096
* total number of pages =3D 1
=20

Results on system2 (RHEL 4.0)
Allocating: 10240 bytes, 100 times.
proc size at start =3D 3350528
proc size at end =3D 4358144: numPages =3D 1064
PageSize =3D 4096
proc grew by =3D 1007616
total number of pages =3D 246

*Allocating: 1024000 all at once.
* total process grew by: 1028096
* total number of pages =3D 251

--=20
Jerry Feldman <gaf-mNDKBlG2WHs at public.gmane.org>
Boston Linux and Unix
PGP key id: 537C5846
PGP Key fingerprint: 3D1B 8377 A3C0 A5F2 ECBB  CA3B 4607 4319 537C 5846