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Lamont Granquist | 1 May 2002 04:21

VM Question (was Re: larger kernel virtual address space)


Does the FreeBSD VM system do O(1) or O(N) searches for gaps in a
processes virtual memory space?

(It may not seem obvious why my question is related to the discussion
below, but trust me, it is...)

On Tue, 30 Apr 2002, David Schultz wrote:
> Thus spake Rohit Grover <rohit <at> gojuryu.com>:
> > I apologize for not checking the FAQs before asking the question.
> > http://www.freebsd.org/doc/en_US.ISO8859-1/books/faq/advanced.html#CHANGE-KERNEL-ADDRESS-SPACE
> >
> > How large can we make the KVA?
>
> This was recently discussed in the thread ``FreeBSD 4.5-STABLE not
> easily scalable to large servers ... ?'' on the stable and current
> lists; you'll probably find the information you want in the archives.
> The short answer is that KVA + UVA <= 4 GB on x86.  So you could raise
> KVA to 3 GB, for instance, but then any given user process would only
> be able to address 1 GB of virtual memory.
>
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>
>

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David Schultz | 1 May 2002 09:23
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Re: VM Question (was Re: larger kernel virtual address space)

Thus spake Lamont Granquist <lamont <at> scriptkiddie.org>:
> Does the FreeBSD VM system do O(1) or O(N) searches for gaps in a
> processes virtual memory space?

I'm not a VM guru, but if I'm reading vm_map.c right, it's O(n)
w.r.t. the number of map entries.  But since map entries are merged
when possible, I would expect the cost to stay fairly low.

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Nelson, Trent . | 1 May 2002 15:40

Kernel spin lock facilities

Hi,

	I'm working on porting the Linux Cisco VPN client kernel module to
FreeBSD.  The API interface between the OS and their actual driver has four
spinlock functions that operate around a handle (void *) to a ``critical
section'':

		CNI_free_spin_lock
		CNI_new_spin_lock
		CNI_spin_lock
		CNI_spin_unlock

	Funnily enough, these wrap the Linux spinlock_t/spin_lock*()
functionality quite nicely.  Does the FreeBSD kernel offer such a trivial
spinlock facility?  If not, could anyone suggest what type of locking
mechanism would best be used?

	Regards,

		Trent. 

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Alfred Perlstein | 1 May 2002 18:15

Re: Kernel spin lock facilities

* Nelson, Trent . <tnelson <at> switch.com> [020501 06:41] wrote:
> Hi,
> 
> 	I'm working on porting the Linux Cisco VPN client kernel module to
> FreeBSD.  The API interface between the OS and their actual driver has four
> spinlock functions that operate around a handle (void *) to a ``critical
> section'':
> 
> 		CNI_free_spin_lock
> 		CNI_new_spin_lock
> 		CNI_spin_lock
> 		CNI_spin_unlock
> 
> 	Funnily enough, these wrap the Linux spinlock_t/spin_lock*()
> functionality quite nicely.  Does the FreeBSD kernel offer such a trivial
> spinlock facility?  If not, could anyone suggest what type of locking
> mechanism would best be used?

man 9 mutex, see the MTX_SPIN section, but you might not need it.

-Alfred

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Lamont Granquist | 1 May 2002 19:28

Re: VM Question (was Re: larger kernel virtual address space)


On Wed, 1 May 2002, David Schultz wrote:
> Thus spake Lamont Granquist <lamont <at> scriptkiddie.org>:
> > Does the FreeBSD VM system do O(1) or O(N) searches for gaps in a
> > processes virtual memory space?
>
> I'm not a VM guru, but if I'm reading vm_map.c right, it's O(n)
> w.r.t. the number of map entries.  But since map entries are merged
> when possible, I would expect the cost to stay fairly low.

I know of one app running on Linux/x86 which spends about 40% of its
kernel time in get_unmapped_pages() (the Linux equivalent).  Trying to
mmap() bits and pieces of 20GB worth of data into a 4GB VM space tends to
lead to a lot of fragmentation.  Be interesting to see if merging would
help, but I'd suggest an O(1) algorithm for this.

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PSI, Mike Smith | 1 May 2002 20:09
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PnP OS Problem

I just noticed that someone else ran into a problem with the solution
"Disable PNP OS in the BIOS". I too ran into that some time back for a
very different problem. If it weren't for the great help from this list,
I would probably still be chasing that one down.

Now I haven't installed FreeBSD for some time so this may be done
already.

Is there ANY benefit to having PNP OS enabled?? I know there are a lot
of problems if it is? If there are no benefits, I would suggest making
this (disabling it) a VERY BLATANT step (suggestion?) in the
installation instructions for FreeBSD. Again, I haven't installed in
quite some time so if this is already in place, I apologize.

Just a thought.

(Not THE) Mike Smith

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Fred Clift | 1 May 2002 21:05

Re: PnP OS Problem

On Wed, 1 May 2002, PSI, Mike Smith wrote:

> Is there ANY benefit to having PNP OS enabled?? I know there are a lot

I dont know about the technical details of FreeBSD in this regard, but one
bennefit I can think of off hand is if you dual-boot to some other
operating system where it is useful.

Fred

--
Fred Clift - fclift <at> verio.net -- Remember: If brute
force doesn't work, you're just not using enough.

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Thomas David Rivers | 1 May 2002 21:47

Anyone using pptp?


Well - I'm still trying to get pptp to cooperate and set up
a VPN connection to a Microsoft VPN server.

I'm just wondering - is there _anyone_ out there that has
met with success using pptp - and, if so, could you share
your /etc/ppp/ppp.conf settings?

	- Many thanks! -
       - Dave Rivers -

--
rivers <at> dignus.com                        Work: (919) 676-0847
Get your mainframe programming tools at http://www.dignus.com

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Lars Eggert | 1 May 2002 22:05
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Re: Anyone using pptp?

Thomas David Rivers wrote:
> Well - I'm still trying to get pptp to cooperate and set up
> a VPN connection to a Microsoft VPN server.
> 
> I'm just wondering - is there _anyone_ out there that has
> met with success using pptp - and, if so, could you share
> your /etc/ppp/ppp.conf settings?

This is a FAQ on -net. There's been a couple of threads on this 
recently, and configuration examples were posted for mpd.

Lars
--

-- 
Lars Eggert <larse <at> isi.edu>           USC Information Sciences Institute
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Thomas David Rivers | 1 May 2002 22:24

Re: Anyone using pptp?

Lars Eggert <larse <at> isi.edu> wrote:
> 
> Thomas David Rivers wrote:
> > Well - I'm still trying to get pptp to cooperate and set up
> > a VPN connection to a Microsoft VPN server.
> > 
> > I'm just wondering - is there _anyone_ out there that has
> > met with success using pptp - and, if so, could you share
> > your /etc/ppp/ppp.conf settings?
> 
> This is a FAQ on -net. There's been a couple of threads on this 
> recently, and configuration examples were posted for mpd.
> 
> Lars

 Duh!!! I didn't even *think* of -net.

 Thanks for the pointer!

	- Dave Rivers -

--
rivers <at> dignus.com                        Work: (919) 676-0847
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Gmane