Short Description of Problem:
Linux 2.6.21.3 does not run properly with 8GB of ram on the Intel 965WH
motherboard.
Long Description of Problem:
When I use 8GB of memory on my x86_64 system, CPU-bound processes are VERY
slow, up to 36x slower than usual. My temporary fix is force Linux to only
use 4GB of memory, I am currently using mem=4096M. I ran memtest86 and the
memory is fine, not a single error. I tried the following to mem= 1024,
2048
4096 and blank "" to let the kernel use all 8GB of memory. What is wrong
with the kernel and how come it cannot use 8GB of memory without slowing
down
all CPU-related processes to a snail-like pace? There is something
horribly
wrong here.
Specifications:
Intel Motherboard: 965WH
Linux Kernel: 2.6.21.3
Distribution: Debian Testing x86_64
GCC: gcc version 4.1.2 20061115 (prerelease) (Debian 4.1.1-21)
Target: x86_64-linux-gnu
Tests:
1. append line = 1024M
top - 18:28:26 up 1 min, 4 users, load average: 0.42, 0.17, 0.06
Tasks: 157 total, 1 running, 156 sleeping, 0 stopped, 0 zombie
Cpu(s): 0.0%us, 0.0%sy, 0.0%ni,100.0%id, 0.0%wa, 0.0%hi, 0.0%si,
0.0%st
Mem: 1027016k total, 964288k used, 62728k free, 1232k buffers
Swap: 16787768k total, 0k used, 16787768k free, 105168k cached
---> STATUS: No problems, box is fine, no lag, etc..
2. append line = 2048M
top - 18:34:23 up 2 min, 2 users, load average: 0.14, 0.14, 0.05
Tasks: 147 total, 1 running, 146 sleeping, 0 stopped, 0 zombie
Cpu(s): 1.7%us, 1.2%sy, 0.4%ni, 95.2%id, 1.5%wa, 0.0%hi, 0.0%si,
0.0%st
Mem: 2059696k total, 956324k used, 1103372k free, 1232k buffers
Swap: 16787768k total, 0k used, 16787768k free, 102924k cached
---> STATUS: No problems, box is fine, no lag, etc..
3. append line = 4096M
top - 18:37:55 up 1 min, 1 user, load average: 0.52, 0.19, 0.07
Tasks: 143 total, 1 running, 142 sleeping, 0 stopped, 0 zombie
Cpu(s): 2.9%us, 2.2%sy, 0.7%ni, 91.6%id, 2.6%wa, 0.0%hi, 0.0%si,
0.0%st
Mem: 3339536k total, 949792k used, 2389744k free, 1232k buffers
Swap: 16787768k total, 0k used, 16787768k free, 99920k cached
$ time ssh p34 uptime
19:00:16 up 1 min, 1 user, load average: 0.67, 0.18, 0.06
real 0m0.159s
user 0m0.013s
sys 0m0.003s
---> STATUS: No problems, box is fine, no lag, etc..
4. append line = "" (use all 8GB)
top - 18:52:50 up 9 min, 1 user, load average: 2.88, 2.43, 1.41
Tasks: 149 total, 3 running, 146 sleeping, 0 stopped, 0 zombie
Cpu(s): 36.3%us, 2.2%sy, 10.3%ni, 50.8%id, 0.4%wa, 0.0%hi, 0.1%si,
0.0%st
Mem: 8104460k total, 1064416k used, 7040044k free, 3296k buffers
Swap: 16787768k total, 0k used, 16787768k free, 201852k cached
$ ssh p34
ssh: connect to host p34 port 22: Connection refused
Machine takes 5-10 minutes to boot, it acts like a 286 computer, about 8
minutes later:
$ time ssh p34 uptime # 5 SECONDS!! 36x slower when using 8GB of RAM
18:51:39 up 8 min, 1 user, load average: 2.74, 2.31, 1.30
real 0m5.757s
user 0m0.015s
sys 0m0.004s
The machine is VERY slow and this is on a gigabit network, I/O does not
seem to be affected but rather, CPU-bound processes.
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
2483 root 25 0 25324 5292 1072 R 96 0.1 4:37.12 mailgraph
3604 logcheck 30 10 3408 1120 544 R 91 0.0 0:03.55 grep
These normally take seconds but when I use all 8GB of memory, it runs
for a very long time.
Conclusion: For now, I will be using mem=4096M until someone can help me
understand what is happening here. Can anyone offer any insight?
I found it interesting in make menuconfig on x86_64 there is no 4GB/64GB
options in the kernel that I remember seeing in 32bit.
