bufpages(5)

NAME

bufpages — the number of 4096-byte memory pages in the file-system buffer cache

VALUES

Minimum

0 or 6 (nbuf*2 or 64 pages)

Maximum

Memory limited

Default

0

Specify integer an value or use an integer formula expression. Use a nonzero value only if dynamic buffer cache is not being used.

DESCRIPTION

bufpages specifies how many 4096-byte memory pages are allocated for the file system buffer cache. These buffers are used for all file system I/O operations, as well as all other block I/O operations in the system (exec, mount, inode reading, and some device drivers).

Specifying a Value for bufpages

To enable dynamic buffer cache allocation, set bufpages to zero. Otherwise, set bufpages to the desired number of 4 KB pages to be allocated for buffer cache. If the value specified for bufpages is nonzero but less than 64, the number is increased at boot time and a message is printed, announcing the change. If bufpages is larger than the maximum supported by the system, the number is decreased at boot time and a message is printed.

Related Parameters and System Values

bufpages interacts with nbuf (see nbuf(5)) as follows:

bufpages	nbuf	Result
zero	zero	Enables dynamic buffer cache.
nonzero	zero	Creates `bufpages/2` buffer headers and allocates `bufpages*4KB` of buffer pool space at system boot time.
zero	nonzero	Allocates `nbuf*2` pages of buffer pool space and creates `nbuf` headers at boot time.
nonzero	nonzero	Allocates `bufpages` pages of buffer pool space and creates `nbuf` buffer headers at boot time. If the two values conflict, such that it is impossible to configure a system using both of them, `bufpages` takes precedence.

bufpages controls how much actual memory is allocated to the buffer pool.

If bufpages is zero at system boot time, the system allocates two pages for every buffer header defined by nbuf. If bufpages and nbuf are both zero, the system enables dynamic buffer cache allocation and allocates a percentage of available memory not less than dbc_min_pct nor more than dbc_max_pct depending on system needs at any given time. (See dbc_min_pct(5) and dbc_max_pct(5).)

The maximum amount of memory that can be allocated to the buffer pool is also affected by the amount of memory allocated to the system for other purposes. Thus, modifying parameters that affect system memory may also affect the maximum amount of memory that can be made available to the buffer pool.

WARNINGS

All HP-UX kernel tunable parameters are release specific. This parameter may be removed or have its meaning changed in future releases of HP-UX.

AUTHOR

bufpages was developed by HP.