ssapkota's questions

Here's a chunk of the top from my server:

PID    USER      PR  NI  VIRT  RES  SHR S %CPU %MEM      TIME+  COMMAND    
18878  www-data  20   0  200m  13m 4704 S    0  0.2    0:00.07  apache2 
12374  root      20   0  197m 9460 4480 S    0  0.1  21212906w  apache2 
9136   root      20   0 79100 3488 2716 S    0  0.0  54518724d  sshd

I know the TIME+ means the total CPU time the task has used since it started. But in the above output, I simply couldn't understand what 21212906w and 54518724d mean? some considerable no of processes are showing the TIME+ with w and d prefixed.
What does this mean? Is the server in trouble?

Just to let you know - the server uptime is 4days.

EDIT:
- I can guess these refer week and days. If so why is it so large considering the uptime?
- The server has 8 cores.

Here the output of free -m:

             total       used       free     shared    buffers     cached
Mem:          7188       6894        294          0        249       5945
-/+ buffers/cache:        698       6489
Swap:            0          0          0

I can see almost 6GB(5945MB) memory out of 7GB is used in caching the files. I know how to flush the caches. My question is: Is possible see which files(or inodes) are being cached?