SYSPTSIZE

[Mike Tracy]

in article <1229 at imshp1.im.se>, orjan at imshp1.im.se (orjan) says:
> 
> 
> I have some questions re. an ICL Clan 6 running Tahoe/SysVR2 (an OEM of
> some CCI machine)
> I want to increase the buffer cache by defining 'buffers' in the
> config file (ie nbuf in /usr/src/uts/machine/cf/space.c).
> Increasing buffers to much gives a messages when booting
> saying 'system page table to small' or something similar and a
> non-working system (process tables etc messed up etc).
> The system administrator manual says (in 'Configuring the system/run time
> calculations') that
> "the amount of physical memory allocated to the buffer cache is
> constrained by the size of the system page tables, among other things".
>                                                    ^^^^^^^^^^^^^^^^^^
> My questions are:
> 
> Sysptsize is defined in .../machine/cf/space.c and SYSPTSIZE in 
> .../machine/ml/sysmap.s.
> How much should/can I increase them to get like a 5 Mb buffer cache
> on a 16 Mb system. At present I only get up to 3.2 Mb without running
> into the system page table limit.
> 
> What are the "other things"  mentioned ?
> 
> 
>    . .
> 	Orjan
> 


If you have source put a print statement in ml/machdep.c before the
sysptsize too small message occurs.. then increase sysptsize by the
amount that it needs to be increased by.

	i.e. ((int)(ecmap+1)&~0xc0000000)/NBPG) - sysptsize

	(This will give you a rough approximation - it may take
	a few iterations; increasing sysptsize each time.)


If not, well, there are a couple of options:

The easy way: increase MAXUSERS.

A way that will take a little more work:
	Buffers typcally take up about 10% of physical memory so for a
	16M system that's 1.6M.  A pte maps 1K. So to map 1.6M takes
	1600 ptes. Now then, sysptsize is the number of ptes that the
	system needs to keep track of it own memory so (assuming the
	current calculation is close - which it really isn't) add an
	additional factor to the equation for SYSPTSIZE in ml/sysmap.s
	to come up with what works best for you.  example: you want 2.0
	M of buffers.  so add 4000 to sysptsize (2.0 - 1.6).
	Increasing inodes, files, etc. from the default will also have
	impacts on the sysptsize.

		mike



-- 
Michael D. Tracy	CCI Computers 
(714)458-7282		9801 Muirlands Boulevard
			Irvine, CA 92718
uunet!ccicpg!mtrac
Newsgroups: cmp.sys.tahoe
Subject: SYSPTSIZE
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in article <1229 at imshp1.im.se>, orjan at imshp1.im.se (orjan) says:
> 
> 
> I have some questions re. an ICL Clan 6 running Tahoe/SysVR2 (an OEM of
> some CCI machine)
> I want to increase the buffer cache by defining 'buffers' in the
> config file (ie nbuf in /usr/src/uts/machine/cf/space.c).
> Increasing buffers to much gives a messages when booting
> saying 'system page table to small' or something similar and a
> non-working system (process tables etc messed up etc).
> The system administrator manual says (in 'Configuring the system/run time
> calculations') that
> "the amount of physical memory allocated to the buffer cache is
> constrained by the size of the system page tables, among other things".
>                                                    ^^^^^^^^^^^^^^^^^^
> My questions are:
> 
> Sysptsize is defined in .../machine/cf/space.c and SYSPTSIZE in 
> .../machine/ml/sysmap.s.
> How much should/can I increase them to get like a 5 Mb buffer cache
> on a 16 Mb system. At present I only get up to 3.2 Mb without running
> into the system page table limit.
> 
> What are the "other things"  mentioned ?
> 
> 
>    . .
> 	Orjan
> 


If you have source put a print statement in ml/machdep.c before the
sysptsize too small message occurs.. then increase sysptsize by the
amount that it needs to be increased by.

	i.e. ((int)(ecmap+1)&~0xc0000000)/NBPG) - sysptsize

	(This will give you a rough approximation - it may take
	a few iterations; increasing sysptsize each time.)


If not, well, there are a couple of options:

The easy way: increase MAXUSERS.

A way that will take a little more work:
	Buffers typcally take up about 10% of physical memory so for a
	16M system that's 1.6M.  A pte maps 1K. So to map 1.6M takes
	1600 ptes. Now then, sysptsize is the number of ptes that the
	system needs to keep track of it own memory so (assuming the
	current calculation is close - which it really isn't) add an
	additional factor to the equation for SYSPTSIZE in ml/sysmap.s
	to come up with what works best for you.  example: you want 2.0
	M of buffers.  so add 4000 to sysptsize (2.0 - 1.6).
	Increasing inodes, files, etc. from the default will also have
	impacts on the sysptsize.

		mike



-- 
Michael D. Tracy	CCI Computers 
(714)458-7282		9801 Muirlands Boulevard
			Irvine, CA 92718
uunet!ccicpg!mtrac