Date: Tue, 19 Jun 2001 11:15:01 +0530 (IST) From: "Ashutosh S. Rajekar" <asr@softhome.net> To: Matt Dillon <dillon@earth.backplane.com> Cc: freebsd-hackers@FreeBSD.ORG Subject: Re: max kernel memory Message-ID: <Pine.LNX.4.21.0106191046050.991-100000@vangogh.indranetworks.com> In-Reply-To: <200106181757.f5IHvKK16658@earth.backplane.com>
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On Mon, 18 Jun 2001, Matt Dillon wrote:
>
> 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
Most of the resources will go into mbufs, clusters, socket structures,
PCBs, etc. I mean, supporting a million TCP/IP connections is the primary
goal. If setting aside more memory for kernel usage doesn't work out, then
I guess I'll have to have some user-level dummy processes that just hold
memory for me, and pass it on whenever required. But memory bandwidth is
still going to be an issue. (not to forget user-kernel switches,
user-kernel copy, etc.).
> 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.
An associated question: along with this, changing the kernel to use only
PDEs should be better for TLB performance. Mapping 4Mb at a time would
definitely be much better than 4k. I'm talking of having the entire kernel
(at least the code) find mappings in the TLB, and keeping 4Mb mappings
might just do the trick.
I did see pmap_kmem_choose() being called pretty early in
pmap_bootstrap(), but it looks like it's doing that for a single
page; what I want is to have 4M mappings for all pages in the system.
Or have I overlooked something ? Any comments ?
-ASR
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