Can 10M Buffer Ceiling be lowere?

[Brian Bobowski]

Kris Kennaway wrote:

>On Wed, Dec 01, 2004 at 03:27:11AM +0000, r.p.demarco at att.net wrote:
>  
>
>>     A technical question:
>>
>>     I have an old NEC computer (c. 1997) running 5.3-RELEASE with
>>48M of RAM.  Getting a new computer isn't an option right now, but
>>I would like to get as much out of my memory as possible.
>>     My /boot/kernel/kernel file is about 3M, and from the initial
>>boot: 
>>		real memory  = 50331648 (48 MB)
>>		avail memory = 43896832 (41 MB)
>>it appears this kernel takes up about 7M of memory with one screen saver
>>kld loaded.  With a few unneeded services (cron, sendmail) disabled, I
>>start off with about 26M free after a fresh reboot with just root logged in,
>>running `top'.  Looking at top, I noticed:
>>
>>                Mem: 4320K Active, 15M Inact, 12M Wired, 10M Buf, 11M Free
>>                                                         ^^^
>>
>>     From TOP(1):
>>
>>                Buf: number of pages used for BIO-level disk caching
>>
>>     Actually, the 10M is after some disk usage (it starts ~6M).
>>It never gets above 10M.  Is there anyway to adjust this, to
>>(say) a maximum of 5M?  Yes, a new 256 MB RAM system would be nice,
>>but until then, I would like to avoid serious paging running xclock :)
>>Thanks,
>>    
>>
>
>There's no point, that memory will be used if demanded.  Note that you
>still have 11M free in your example, so throwing away 6MB that is used
>for caching would only *reduce* performance.
>
>Kris
>  
>
Stated otherwise, I recall reading that FreeBSD considers unused memory 
to be wasted memory. If you had other stuff taking up memory, it might 
not use that much for caching; as it is, though, it's only taking 
advantage of memory which is otherwise just sucking up power to keep 
ready. Its activity, based on this, is causing you no harm. (I don't 
know if my 32MB machine, which reports 440K free from top, is suffering 
as a result, but I've certainly not noticed any difficulty when loading 
web pages that couldn't be as adequately explained by the relatively 
slow 166MHz CPU.)

Also note that cron is responsible for such things as the routine system 
checks; if you really insist on disabling cron, you might need to audit 
your system a bit more aggressively.

-BB