Jeremy Chadwick pisze:
On Thu, Sep 25, 2008 at 12:26:58PM +0200, Bartosz Stec wrote:
Today I've experienced zfs-related kernel panic. Log says:
savecore: reboot after panic: kmem_malloc(131072): kmem_map too
small: 327684096 total allocated
Reported amount of memory (327684096) is wrong, because i made suggested
tuning in my loader.conf:
vm.kmem_size="512M"
vm.kmem_size_max="512M"
Just to be sure:
# sysctl vm | grep kmem
vm.kmem_size: 536870912
vm.kmem_size_min: 0
vm.kmem_size_max: 536870912
vm.kmem_size_scale: 3
Am I missing something?
I believe this is normal. The amount shown in "total allocated" will
not match what you have vm.kmem_size or vm.kmem_size_max set to.
Someone more familiar with the VM can explain why this is, but as I
understand it, it's 100% normal.
Thanks for explaining. This part of tuning guide confused me:
"I was able to generate the following kernel panic in less than a
minute by copying files from a linux server connected via gigabit
crossover:
Apr 8 06:46:08 nas savecore: reboot after panic: kmem_malloc(131072): kmem_map too small: 528273408 total allocated
As you can see, this is *with* vm.kmem_size="512M"!"
I've just expected similiar numbers in my case.
Your options are:
1) Consider increasing it from 512M to something like 1.5GB; do not
increase it past that on RELENG_7, as there isn't support for more than
2GB total. For example, on a 1GB memory machine, I often recommend
768M. On 2GB machines, 1536M. You will need to run -CURRENT if you
want more.
2) Tune ZFS aggressively. Start by setting vfs.zfs.arc_min="16M"
and vfs.zfs.arc_max="64M".
If your machine has some small amount of memory (768MB, 1GB, etc.),
then you probably shouldn't be using ZFS.
Problem occured on i386 machine with 1GB of memory and 7.1-pre (3HDD,
40GB, RAIDZ1). I know that i386 is highly unrecommended for ZFS, but
it's just a home box for testing and learning purposes - I just want to
know what I'm doing and what should I expect when I decide to put ZFS on
server machines :) Currently, from posts on freebsd-fs, I conclude that
even with a gigs of kmem and using AMD64, we still can experience panic
from kmem_malloc. Manual tuning is hard for me because I'm not familiar
with BSD kernel code nor kernel memory management. I'm just an end-user
who love concepts of ZFS and wait for it to be (more) stable. Of course
I've followed tuning guide carefully.
So, for now, I will add another 512MB of memory and increse vm.kmem_size
and do more tests. Thanks once again for explaining and suggestions.
Good luck with ZFS everyone! :)
--
Bartosz Stec
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