Re: Slow-down every 30 secs

From: Arjan de Vet <>
Date: Wed, 25 Feb 1998 15:52:26 +0100 (CET)

In article <> you write:

>'sysctl kern.update'
>Should this give the value '30' try
>'sysctl -w kern.update=2'

On FreeBSD-current (to become 3.0) there is a sysctl variable
vfs.numdirtybuffers which tells you the current number of dirty buffers (I
patched the systat program to show it in the -vmstat display).

There are two other variables vfs.lodirtybuffers and vfs.hidirtybuffers
which can be tuned to avoid all dirty buffers being flushed to disk only
each X seconds by update. Flushing starts when numdirtybuffers >
hidirtybuffers and flushing ends when numdirtybuffers < lodirtybuffers. By
carefully choosing these values you can avoid that only update does sync()s
which can take multiple seconds to complete.

Received on Wed Feb 25 1998 - 06:55:50 MST

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