SUMMARY : buffer cache

From: Wai-kong Yu (wai-kong@abcomp.UUCP)
Date: Mon Feb 01 1993 - 17:35:37 CST

Thanks to all who responded to message.

My original message :

        Is it possible to increase the size of the buffer cache on a SunOS 4.1.3
        system (NBUF, MBUF, etc) ? I read somewhere that it is assigned dynamically in SunOS 4.1.X and SVR4 and that you can't change it manually. Is this
        true ?

The answers :

Hal Stern - NE Area Systems Engineer

in solaris 1.x and 2.x (4.1.x and 5.x), the old berkeley
buffer cache (used to hold filesystem pages) is gone.
all of free memory is used, so there is no need to
ever "increase" it -- it's as large as it can be by

the buffer cache itself, though, still exists. it is
used to move metadata like inodes, cylinder groups and
superblocks back and forth to the disk. in 4.1.3
and solaris 2.x, this cache is sized optimally by the
kernel -- no need to tune it

Christian Lawrence

if you're talking about what use to be known as **THE** buffer cache (i.e. mbuf
which was a reserved area holding file blocks) it is no longer used since Sun
moved to a newer berkeley derivative that directly maps file pages into the
process space (instead of copying in/out). essentially, this scheme can use the
entire virtual memory space as a cache -- overwriting pages when necessary
based on some permutation of a last used algorithm.

some other buffers are also allocated dynamically **IF** default values are
set in the kernel -- but many of these can be overridden by simply changing
the value. the "file cache" does not fall into this category. if you want to
change it ..... just add/delete memory and everything else is magic !

Kevin Sheehan {Consulting Poster Child}

It is more accurate to say that it makes little difference. Memory
is just viewed as a cache for stuff on disk - pages for I/O are treated
just like pages for text/data, they all compete on an equal basis.

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