Kernel Parameters and System Performance

Many basic parameters (or tables) within the kernel are calculated from the value of the maxusers parameter. Tables are allocated space dynamically. However, you can set maximums for these tables to ensure that applications won't take up large amounts of memory.

By default, maxusers is approximately set to the number of Mbytes of physical memory on the system. However, the system will never set maxusers higher than 1024. The maximum value of maxusers is 2048, which can be set by modifying the /etc/system file.

See Chapter 66, Tuning Kernel Parameters (Tasks), and system(3S) for details on kernel parameters.

In addition to maxusers, a number of kernel parameters are allocated dynamically based on the amount of physical memory on the system, as shown in Table 62-6 below.

Table 62-6 Kernel Parameters

Kernel Parameter	Description
ufs_ninode	The maximum size of the inode table
ncsize	The size of the directory name lookup cache
max_nprocs	The maximum size of the process
ndquot	The number of disk quota structures
maxuprc	The maximum number of user processes per user-ID

Table 62-7 lists the default settings for kernel parameters affected by the value assigned to maxusers.

Table 62-7 Default Settings for Kernel Parameters

Kernel Table	Variable	Default Setting
Inode	ufs_ninode	max_nprocs + 16 + maxusers + 64
Name cache	ncsize	max_nprocs + 16 + maxusers + 64
Process	max_nprocs	10 + 16 * maxusers
Quota table	ndquot	(maxusers * NMOUNT) / 4 + max_nprocs
User process	maxuprc	max_nprocs - 5

See Chapter 66, Tuning Kernel Parameters (Tasks), for a description of the kernel parameters and how to change the default values.