Subject: Re: buffer cache tuning - running out of kernel virtual space
To: Chuck Silvers <>
From: Paul Kranenburg <>
List: tech-kern
Date: 12/12/2005 09:40:01
> I see that a mechanism already exists to limit virtual space usage by
> the buffer cache, buf_setvalimit(), which is used by alpha, mips, sparc
> and vax.  however, it seems to me that the usage for all but sparc is wrong
> since it sets the limit to whatever the limit would have been anyway:
> 	bufsz = buf_memcalc();
> 	buf_setvalimit(bufsz);
> or maybe this is just supposed to keep people from tuning the limit higher
> than its original value.  I'm not sure why that would be desirable though.
> does anyone know why these are here?  if not, I'll remove them.  (the sparc
> instance actually imposes a smaller limit, so I'll leave that one.)

This particular sequence was introduced in ports that used to consider
the amount of virtual memory allocated to the buffer cache (i.e.  `nbuf')
while setting up their physical memory management module.