CVS commit: src/sys

[Thor Lancelot Simon <tls%netbsd.org@localhost>]

Module Name:    src
Committed By:   tls
Date:           Fri Jan 30 11:32:16 UTC 2004

Modified Files:
        src/sys/kern: vfs_bio.c
        src/sys/uvm: uvm_pdaemon.c

Log Message:
Buffer cache fixes to avoid thrashing between high and low water marks
and uncontrolled growth.

The key fix is from Dan Carasone, who noticed that buf_canfree() was
counting in _bytes_ but freeing in _buffers_, which caused the instant
drop to lowater observed by some users.

We now control the rate of growth; the probability of getting a new
allocation is inversely proportional to the current size of the
cache.  This idea is from a long-ago conversation with Kirk McKusick
and, if memory serves, was used for the file-system cache in some
other BSD variant at some point in history.

With growth and shrinkage more or less dealt with, we return the
default maximum cache size to 15%.  The default _minimum_ cache size
is raised from 1/16 of the maximum cache size to 1/8, since 1/16 was
chosen when the maximum size was 30% of memory.

Finally, after observing the behaviour of the pagedaemon and the
buffer cache drainer under pathological workloads (e.g. a benchmark
that steps through 75% of available memory backwards) I have moved
the call to buf_drain() to the beginning of the pagedaemon from the
end; if the pagedaemon bogs down, it still won't get run as often
as it should, but at least this way it will see the state of the
free count and free target _before_ the scan step does its thing.


To generate a diff of this commit:
cvs rdiff -r1.113 -r1.114 src/sys/kern/vfs_bio.c
cvs rdiff -r1.57 -r1.58 src/sys/uvm/uvm_pdaemon.c

Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.