[CentOS] 2.6 memory management question

tblader

tblader at flambeau.com
Tue Apr 10 13:37:13 UTC 2007


Hello all.
I have a centos 4.4 box (2.6.9-42.0.10.ELsmp) with 7gig of ram that
doesn't seem to be using swap (also 7gig now).  I say "seem" because
I've noticed ram utilization run around 95% (with oracle and friends
running) and then firing up a couple apps to use that last 5% will
stop the machine dead in it's tracks.

I ran across some reading[0] about /proc/sys/vm/swappiness and how it
affects the kernels decisions when dealing with swap, but it's not
all that clear to me whether this is the source of the problem.
It seems like the kernel just isn't using swap at all.

I've double checked my swap partition in fstab, ran mkswap again,
double checked it's availability with vmstat -s  but still it's
just not getting used.  Sunday, the box died around 3am and sar
seems to show memory use on the rise right up till it hurled[1]
(I just stuck another gig in the box monday, so sar only shows
6gig on sunday)


Anyone know whats up with this?
PS: swap is an LVM partition.

Thanks
Thomas



[0] - http://lwn.net/Articles/83588/
[1] - sar -A
12:00:01 AM kbmemfree kbmemused  %memused kbbuffers  kbcached kbswpfree kbswpused  %swpused  kbswpcad
...
02:40:01 AM    197656   5909384     96.76    203308   4066344  16383992         0      0.00         0
02:50:01 AM    191728   5915312     96.86    203320   4066400  16383992         0      0.00         0
03:00:01 AM    185584   5921456     96.96    203336   4067132  16383992         0      0.00         0
03:10:01 AM    185712   5921328     96.96    203344   4067872  16383992         0      0.00         0
Average:       191895   5915145     96.86    203221   4063819  16383992         0      0.00         0


12:00:01 AM  pswpin/s pswpout/s
...
02:00:01 AM      0.00      0.00
02:10:01 AM      0.00      0.00
02:20:01 AM      0.00      0.00
02:30:01 AM      0.00      0.00
02:40:01 AM      0.00      0.00
02:50:01 AM      0.00      0.00
03:00:01 AM      0.00      0.00
03:10:01 AM      0.00      0.00
Average:         0.00      0.00




-- 

Flambeau Inc. Technology Center - Baraboo, WI
Email    : tblader at flambeau.com
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