Solaris Application Programming, 1/e - Chapter 4 - Parent Directory

4.3 TOOLS THAT REPORT CURRENT SYSTEM STATUS 57
page: The columns labeled re to sr refer to paging information. The re column
lists the number of pages containing data from files, either executables
or data, that have been accessed again and therefore reclaimed from the list
of free pages. The mf column lists the number of minor page faults, in which a
page was mapped into the process that needed it. The pi column lists the
number of kilobytes paged in from disk and the po column lists the number of
kilobytes paged out to disk. The de column lists the anticipated short-term
memory shortfall in kilobytes, which gives the page scanner a target number
of pages to free up. The sr column lists the number of pages scanned per second.
A high scan rate (sr) is also an indication of low memory, and that the
machine is having to search through memory to find pages to send to disk.
The solution is to either run fewer applications or put more memory into the
machine. Continuously high values of pi and po indicate significant disk
activity, due to either a high volume of I/O or to paging of data to and from
disk when the system runs low on memory.
disk: There is space to report on up to four disk drives, and these columns
show the number of disk operations per second for each of the four drives.
faults: There are three columns on faults (i.e., traps and interrupts). The in
column lists the number of interrupts; these are used for tasks such as handling
a packet of data from the network interface card. The sy column lists
the number of system calls; these are calls into the kernel for the system to
perform a task. The cs column lists the number of context switches, whereby
one thread leaves the CPU and another is placed on the CPU.
cpu: The final three columns are the percentage of user, system, and idle
time. This is an aggregate over all the processors. Example 4.11 shows output
from a two-CPU machine. With an idle time of 50%, this can mean that
both CPUs are busy, but each only half the time, or that only one of the two
CPUs is busy. In an ideal world, most of the time should be spent in user
code, performing computations, rather than in the system, managing
resources. Of course, this does not mean that the time in user code is being
spent efficiently, just that the time isn’t spent in the kernel or being idle.
High levels of system time mean something is wrong, or the application is
making many system calls. Investigating the cause of high system time is
always worthwhile.
4.3.3 Reporting Swap File Usage (swap)
Swap space is disk space reserved for anonymous data (data that is not otherwise
held on a filesystem). You can use the swap command to add and delete swap space
from a system. It can also list the locations of swap space using the -l flag, and