The Linux kernel needs to allocate memory for temporary objects such as task or device structures and inodes. The caching memory allocator manages caches of these types of objects. The modern Linux kernel implements this caching memory allocator to hold the caches called the slabs. Different types of slab caches are maintained by the slab allocator. This article concentrates on the slabtop command which shows real-time kernel slab cache information.
1. Command Usage:
The command is simple to use. Default execution does not mandate any arguments to the command. But it does require root privileges to access the kernel slab information. Executing the command as normal user gives following error:
You can run it by prepending "sudo" with slabtop. The default output looks like:
To quit from slabtop, just hit 'q' like you do for top command.
2. Slabtop options:
2.1 Display Interval:
By default slabtop refreshes every 3 seconds. But if you want, you can provide the refreshing interval in seconds with -d or --delay=N option:
2.2 Sort criteria:
There are many fields in slabtop output. The -s or --sort=S option sorts the output according to the mentioned sort criteria. This option will be discussed in detail in the next section.
2.3 Output once:
The -o or --once option does not refresh the output, instead it just throws the output once on STDOUT and exits.
2.4 Version info:
The -V or --version displays the version of the command and exits.
The common option, -h or --help displays usage of the command.
3. Sort Criteria:
The sort criteria determines which slab caches are displayed on top. Following are the sort criteria for slabtop:
Caches can be sorted by number of active objects with "a".
The Objects per Slab can be selected with "b".
3.3 CACHE SIZE:
For selecting cache size, you need to provide "c".
The number of slabs. Select it with "l"
3.5 Active Slabs:
The number of Active Slabs. (Note that this is different from number of Active Objects described above.) Use "v" to sort according to this criteria.
Name of cache. Corresponding character is "n"
To sort by number of objects, use "o"
3.8 Pages Per Slab:
"p" will sort by pages per slab
3.9 OBJ SIZE:
The object size is sorted by "s"
"u" sorts by the cache utilization.