Subject: Re: Possible serious bug in NetBSD-1.6.1_RC2
To: Greg Oster <>
From: Brian Buhrow <>
List: current-users
Date: 03/11/2003 13:41:47
	Hello Greg.  Another thought I had is that since kernel memory is
sized dynamically according to the total amount of RAM, I may not have seen
this problem before because the  machine I was using had 256MB of ram.  If,
as you say, and I tend to agree, that the raidframe drivers don't exhibit
much in the way of memory leaks, it makes sense that if the space available
is sufficient, it will always be sufficient.  Is theree some part of vmstat,
or some other command, which will tell how much kernel RAM is currently in


On Mar 11,  2:13pm, Greg Oster wrote:
} Subject: Re: Possible serious bug in NetBSD-1.6.1_RC2
} Brian Buhrow writes:
} > 	Hello Greg.  If I understand your message correctly, then I have a
} > couple of questions and observations.
} > 
} > 1.  According to sysctl, nkmempages is already at 8102.  This is about 33MB
} > of memory, if my calculations are correct.  Using the value 8192 would be
} > about 35MB of memory,not much more than is currently in use.  Is there a
} > limit to the number of pages I can allocate?  Must it be a power of 2? 
} Hmmmmm... On a machine w/ 512MB RAM I see:
} oster@merlin-39> sysctl -a | grep kmem
} vm.nkmempages = 32739
} On one with 256MB RAM, I get:
} cs# sysctl -a | grep kmem
} vm.nkmempages = 16354
} So maybe try 16384 instead of 8192?  (I would have though 8192 should have 
} been more than sufficient tho!!)  I'm not sure what the limits are, nor whether
} the values need to be a power of two or not.
} >  In
} > case it helps with the sizing, right now, under normal operation, the
} > machine lasts 28-36 hours before it hangs or panics.  If I perform the
} > exercise I listed in the previous e-mail, it hangs immediately.
} I'll try to dig up some time this evening to try to reproduce the problem on 
} my test box. (It only has 128MB RAM too...)  It's sounding like it's seen
} mostly (exclusively?) when swap is on a RAID 5 set.
} > 2.  I'm notcertain, but my guess is that the reason raid5 works under 1.5R
} > and not 1.6 is not so much due to the changes in raidframe itself, but,
} > rather, changes in the way kernel memory is managed by uvm.  They may be
} > only tuning changes, but something definitely changed.
} [snip]
} That sounds suspiciously correct... (depending on how some dynamic kernel 
} memory allocation might be, it could be that the RAID driver exhausts kernel
} memory when trying to page out stuff...  I need to do some testing it seems...)
} Later...
} Greg Oster
>-- End of excerpt from Greg Oster