>
>:Hi,
>:
>:I'm trying to give the kernel (4.0-RELEASE) 2Gb of memory to work with. I
>:can afford to have 4Gb of physical memory on one of my servers, and hence
>:the experiments.
>:
>:Is it safe to play around with KERNBASE, and get away without breaking
>:code ? Is there any other advisable method if this one is risky ?
>:
>:-ASR
>
> Yes, you can change KERNBASE. I'm not entirely sure but I believe if
> you have an old set of bootblocks you may have to reinstall them to
> get a set that is kernbase-agnostic. e.g. the disklabel -B command on
> the appropriate slice.
>
> DG changed KERNBASE a while back to reserve a gigabyte of VM for the
> kernel. This should be sufficient on a 4G machine but it depends where
> your resources are going. If your server's resources are user-process
> centric then you don't need to change KERNBASE. If your server's
> resources are network-mbuf centric then you may have to give the kernel
> more KVM (e.g. like 2GB instead of 1GB... 0x80000000 instead of
> 0xC0000000). But be careful. The more KVM reserved for the kernel, the
> less VM is available for user processes to allocate and mmap.
>
> I'm sure people who run 4G machines can give you better information, I've
> never run anything larger then 2G myself, though expect down the line
> I'll begin needing 4G machines to support larger databases.
Don't forget to also change NKPDE as well when relocating the start of
kernel VM. For kernbase = 0x80000000 on a non-SMP machine, NKPDE needs to
be 511.
-DG
David Greenman
Co-founder, The FreeBSD Project - http://www.freebsd.org
President, TeraSolutions, Inc. - http://www.terasolutions.com
Pave the road of life with opportunities.
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