What is kernel_task, and why is it taking up so much RAM and CPU?

Question

I have recently upgraded to OS X Mavericks, and despite promises of extreme performance, my MPB has been running slower than ever before. According to Activity Monitor, "kernal_task" is taking up 600+ MB of RAM and hasn't dropped since I upgraded. It's also been taking between 4% and 8% of my CPU. When I first upgraded, there was a little alert message that said it was optomizing my system, and it may slow down the computer and decrease battery life. The message lasted for two days, then finally went away. (I didn't close it, so I assumed it had finished.) However, kernal_task, which I thought was the optomization, has been on the top of the list of RAM usage and top 3 on the list of % CPU since I upgraded. PLEASE tell me what it is, and how I can decrease it's toll on my performance! It won't let me stop the task or even get more information on it when I select it on the list of processes. Also, on a side note, Activity Monitor used to let you change its dock icon to a pie chart showing memory usage. Unfortunately, this feature seems to be gone. Is there any way I can get it back or use a different app? I don't want to have it open on top of my stuff or as a window, I would like to see it in the dock. In fact, the chart isn't even in the memory tab of the Activity Monitor application anymore!
Thank you so much to whoever can help me out in my panic and frustration. For the record, I am actually really great at computers, but I turned to the support community because I'm sure there's someone out there with more knowledge than me, even though I'm not a tech-illiterate person...
Dan
Specs: (Per the System Information App)
Model Name:          MacBook Pro
  Model Identifier:          MacBookPro6,1
  Processor Name:          Intel Core i7
  Processor Speed:          2.8 GHz
  Number of Processors:          1
  Total Number of Cores:          2
  L2 Cache (per Core):          256 KB
  L3 Cache:          4 MB
  Memory:          8 GB
  Processor Interconnect Speed:          4.8 GT/s
  Boot ROM Version:          MBP61.0057.B0F
  SMC Version (system):          1.57f18
  Sudden Motion Sensor:
  State:          Enabled
Also, I'm on a MacBook Pro 17" with a 500GB hard drive (and only 70GB free, but I use an external 2TB as my main drive). It is a mid-2010 build, and I bought it certified refurbished.

Answer 1

That's not very high. Mine is over 1 GB. Typical is around 5-800 GBs depending upon what tasks are running.
You don't need to add more RAM, just be careful not to run more concurrent tasks than are appropriate for your memory usage profile. It's really not a big deal unless it gets to 600 GBs. Then you have a problem.
I disagree with McBlob about free disk space. Keep at least 10% of the drive's capacity as free space. For you that's 50 GBs, and that's adequate.