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Old 12-29-2005, 09:37 PM   #1
joelunch
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Memory Usage Spaw Usage Swappiness Issues


Ok we moved 300 sites that we are hosting from a 3gig P4 HT machine to basically the same machine both with 1 gig of ram. First machine running Red Hat 9(kernel 2.4.20-16.9smp), second machine running Centos 4.2(kernel 2.6.9-22.0.1.ELsmp).
Basically on the first machine all ram would be used up (as desired) but on the second machine most of the ram appears to never be touched. As a result there appears to be lots of swapping and the load goes upto 5 to 10 and kswapd appears in top. Below is the top memory usage on our new server

Code:
top - 14:23:58 up 7 days,  5:32,  5 users,  load average: 0.77, 0.65, 0.74
Tasks: 135 total,   1 running, 134 sleeping,   0 stopped,   0 zombie
Cpu0  :  0.3% us,  1.3% sy,  0.3% ni, 97.0% id,  0.7% wa,  0.3% hi,  0.0% si
Cpu1  :  2.3% us,  0.3% sy,  0.0% ni, 97.3% id,  0.0% wa,  0.0% hi,  0.0% si
Mem:   1017676k total,   358320k used,   659356k free,     5764k buffers
Swap:  2040120k total,   249412k used,  1790708k free,    41064k cached


new server
free -m
             total       used       free     shared    buffers     cached
Mem:           993        339        654          0          4         38
-/+ buffers/cache:        295        698
Swap:         1992        243       1748

old server 
free -m
             total       used       free     shared    buffers     cached
Mem:           998        961         36          0        458        270
-/+ buffers/cache:        232        766
Swap:         1019         21        997
We have tried changing the swappiness down by ten at a time to 5 and are still having issues. It appears that only about a third of real memory is ever used on the new server( and the machine then does lots of swapping). Could it be that the standard kernel isn't compiled for large memory support of 1 gig? Is there some way that we can check this? Does anyone have any other ideas?
 
Old 12-29-2005, 10:36 PM   #2
foo_bar_foo
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i would say just off hand that that kernel is patched to the point of dysfunction.
 
Old 12-29-2005, 10:39 PM   #3
foo_bar_foo
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i would say just off hand that that kernel is patched to the point of dysfunction. definitely build a new one (not using that same minor version source code). possibly the one from centOS 4.1

i saw a thread on webhostingtalk about exactly this with lots of other people reporting exactly the same awfull behaviour.
 
Old 01-04-2006, 06:16 PM   #4
joelunch
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Ok we upgraded to 2.6.15 and the problem looks totally resolved. We are now using 2452k of swap and not 1+ gig. So a kernel upgrade is recommended if you are having issues.
 
  


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