Subject: re: Ungraceful low memory issue
To: matthew green <>
From: John Klos <>
List: current-users
Date: 08/14/2004 13:50:51
> > sd2(esiop0:0:2:0): unable to allocate scsipi_xfer
>   The min threshhold (16*1024) will almost never be used as it means a
>   memory size of 20*2*8k == 320k for a pagesize of 8k. So it will always
>   clamp uvmexp.freemin to 256k which is very low for modern memory sizes.
> these values actually come from 4.4BSD/machvm completely untouched.
> many many years ago i spent some time trying to determine better values
> for this but i didn't really discover anything conclusive...
> however, this shouldn't really affect the pool allocator... we already
> reserve a bunch of pages for such conditions i thought.

4.4BSD and NetBSD are really good at dealing with small amounts of system 
memory, which is great; I can't remember the last time I've ever seen an 8 
meg system panic from heavy use.

On the other hand, when my systems have 1.5 or 2 gigs of memory, "wasting" 
a few megabytes (or even tens of megabytes) by overallocating stuff to 
make sure we never get into a panic state really would not bug me. 
Stability is much more important with colocated servers than most anything 
else, and it'd be nice to see large memory systems not panic.

The issue now, I suppose, is finding someone who knows more about the 
intimate details of the kernel memory allocation system... anyone?

John Klos