[9fans] memory

[9fans] memory

[tapique]

hi,
can someone show me the pros and cons of having kernel and user memory spaces
separated? just would like to learn...
thanks,
++pac.


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Re: [9fans] memory

[Russ Cox]

pro: errant user programs can't scribble all over the
kernel's memory and cause it to crash.  
con: that makes it harder to simulate dos and windows.

russ

On Mon, 7 Feb 2005 08:16:22 +0100, tapique@tiscali.cz
<tapique@tiscali.cz> wrote:
> hi,
> can someone show me the pros and cons of having kernel and user memory spaces
> separated? just would like to learn...
> thanks,
> ++pac.
> 
> --------------------------
> Posílejte SMS přes internet zdarma a bez reklamy. Pouze s TISCALI.
> Více na http://www.tiscali.cz
> 
>

Re: [9fans] memory

[Lucio De Re]

> con: that makes it harder to simulate dos and windows.

Con? Con?!  Surely you jest?

++L

Re: [9fans] memory

[arisawa]

Just translation from Robert, avoiding zero division.

#!/bin/rc
all=`{cat /dev/swap | sed 's,/, ,g'}
echo '
pageinmb = 4096/(1024*1024)
mem = '$all(1)^'*pageinmb
memtotal = '$all(2)^'*pageinmb
memperc = mem*100/memtotal
swap = '$all(4)^'*pageinmb
swaptotal = '$all(5)^'*pageinmb
if(swaptotal != 0){
         swapperc = swap*100/swaptotal
} else {
         swapperc = 0
}
print "memory: ",int(mem),"MB used (",int(memperc),"% of 
",int(memtotal),"MB).\n"
print "swap: ",int(swap),"MB used (",int(swapperc),"% of 
",int(swaptotal),"MB).\n"
' | hoc


Kenji Arisawa

Re: [9fans] memory

[Robert Raschke]

After Andrey sent round his useful little script recently, I tarted
it up ever so slightly to show percentages, and since I only think in
MB these days, added some truncating:

cpu% cat /bin/mem
#!/bin/rc

# show available and used memory in
# user-discernible format.

# Thanks goes to Andrey Mirtchovski for the original.

all=`{cat /dev/swap | sed 's,/, ,g'}

pageinmb = `{echo '4096/(1024*1024)' | hoc }

mem = `{echo 'int('^$all(1)^'*'^$pageinmb^')' | hoc }
memtotal = `{echo 'int('^$all(2)^'*'^$pageinmb^')' | hoc}
memperc = `{echo 'int('^$mem^'*100/'^$memtotal^')' | hoc}
swap = `{echo 'int('^$all(4)^'*'^$pageinmb^')' | hoc }
swaptotal = `{echo 'int('^$all(5)^'*'^$pageinmb^')' | hoc}
swapperc = `{echo 'int('^$swap^'*100/'^$swaptotal^')' | hoc}

echo 'memory: '^$mem^' MB used ('^$memperc^'% of '^$memtotal^' MB).'
echo 'swap: '^$swap^' MB used ('^$swapperc^'% of '^$swaptotal^' MB).'

cpu% mem
memory: 37 MB used (42% of 87 MB).
swap: 0 MB used (0% of 512 MB).
cpu%

Robby

Re: [9fans] memory

[andrey mirtchovski]

i find the following useful.  i'm lazy and i'm not good at multiplying
by blocksize in my head :)

	plan9% cat /bin/mem
	#!/bin/rc
	
	# show available and used memory in
	# user-discernible format.
	
	all=`{cat /dev/swap | sed 's,/, ,g'}
	
	# 4096/(1024*1024)
	pageinmb=0.00390625 
	
	mem = `{echo $all(1)^'*'^$pageinmb | hoc }
	memtotal = `{echo $all(2)^'*'^$pageinmb | hoc}
	swap = `{echo $all(4)^'*'^$pageinmb | hoc }
	swaptotal = `{echo $all(5)^'*'^$pageinmb | hoc}
	
	echo memory: $mem MB used. $memtotal MB total
	echo swap: $swap MB used. $swaptotal MB total
	
	plan9% 

it helps those times when one has forgotten to turn on the swap or is
using only 16 megs of ram instead of the available 128 :)

it output looks like this on plan9.ucalgary.ca (10000 blocks fossil cache):

	plan9% mem
	memory: 126.6640625 MB used. 430.27734375 MB total
	swap: 0 MB used. 611.76953125 MB total
	plan9% 

Re: [9fans] memory

[geoff]

Actually, that's: any setting higher than 90% will revert to the
default (at least on the PC): the code computes userpcnt as 100 -
kernelpercent, and then works with userpcnt.

I'm using *kernelpercent=9 on my terminal, which has 1GB of RAM (for
building CD images in memory).  90MB seems to be adequate for kernel
memory.  Kernel memory is allocated primarily for images (in terminal
kernels) and network buffering.  One might want more network buffering
for faster interfaces, though back- pressure probably limits how much
memory one can profitably use.  I do like not having to worry about
running out of image memory at awkward times (the screen is populated
with windows and you try to open one more, only to have it fail and
spew complaints across the screen).

Re: [9fans] memory

[Tim Newsham]

> Memory test: 393216K OK,

> 58612 free pages, 234448K bytes, 874448K swap

The value that plan9 prints is the number of pages for
the paging system.  This is after memory is taken away
for the kernel itself and the kernel heap.  The amount
that is reserved for kernel vs. user space is configurable
in the pc kernel witht he "*kernelpercent" argument
(see plan9.ini(8)).  If unspecified it will default to
between 40% and 70% of memory going to userspace.  This
seems like a lot of reserved kernel memory to me on
large memory systems (such as yours), but I dont know
all of the implications of using a very low kernel percent.
Btw, any setting lower than 10% will revert to the default.

> ++pac.

Tim N.

Re: [9fans] memory

[Heiko Dudzus]

> at boottime Bios says:
> Memory test: 393216K OK,
> while Plan9 boot:
> 58612 free pages, 234448K bytes, 874448K swap
> (the same says Andrey's 'mem' script)
>  
> what's the matter?

I think, Plan 9 announces the free memory after occupying memory for
the kernel.

Plan 9 preserves more memory for the kernel than its size is because
graphical data for draw(3) will also get stored there.  (If I
understood the paragraph about 'kernelpercent' in plan9.ini(8)
correctly)

[9fans] memory

[cej]

hi,
at boottime Bios says:
Memory test: 393216K OK,
while Plan9 boot:
58612 free pages, 234448K bytes, 874448K swap
(the same says Andrey's 'mem' script)
 
what's the matter?
thanks,
++pac.

Re: [9fans] memory

[presotto]

[-- Attachment #1: Type: text/plain, Size: 508 bytes --]

I was running an 8MB system until 6 months ago.  However, it
would go into swap hell if I tried to make kernels
locally.  It was only usable because I did most things were
done on a cpu server.

With 16mb, you can still run bigger screens than 640x480x8.
at 16MB on a terminal the kernel gives 60% of the memory to
the kernel.  You can make it more still if you want by
including in plan9.ini

	*kernelpercent=90

for example, to get 90%.  Of course, that leaves precious little
for processes.

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From: "Russ Cox" <rsc@plan9.bell-labs.com>
To: 9fans@cse.psu.edu
Subject: [9fans] memory
Date: Mon, 20 Nov 2000 15:48:57 -0500
Message-ID: <20001120204900.B527B199F0@mail.cse.psu.edu>

The install, because it keeps the file system
in RAM, requires 32MB.  I've done an install on a 32MB
system and I was using pretty much all the memory.
As others have pointed out, that's mainly because
the image data is all kept in kernel memory, and the
compressed file system on the floppy is expanded
and kept in memory while being accessed.  
You could run a simple 640x480x8 terminal with
16MB, but I'm not sure how much can be done with
only 8MB.

The ATI video cards come with a wide range of
memory depending mainly on the age of the card.
Others have reported trying the Xpert98 but I don't
remember whether the reports were good or bad.

Russ

Re: [9fans] memory

[Mike Haertel]

>The ATI video cards come with a wide range of
>memory depending mainly on the age of the card.
>Others have reported trying the Xpert98 but I don't
>remember whether the reports were good or bad.

I have Xpert 98's (both AGP and PCI) and they
work really well.

Re: [9fans] memory

[Boyd Roberts]

From: Russ Cox <rsc@plan9.bell-labs.com>

> You could run a simple 640x480x8 terminal with
> 16MB, but I'm not sure how much can be done with
> only 8MB.

i got the 2nd release installed wih 4mb, but i
had to do it in stages; the uncompression just
took the machine out.  it did it piecemeal.

once i'd done it 4Mb was just not enough.  you
could get 8 1/2, sam and maybe a window or two.
finally it would choke.

8Mb would have been better, but i reckon 16Mb
would have been the minimum.

[9fans] memory

[Russ Cox]

The install, because it keeps the file system
in RAM, requires 32MB.  I've done an install on a 32MB
system and I was using pretty much all the memory.
As others have pointed out, that's mainly because
the image data is all kept in kernel memory, and the
compressed file system on the floppy is expanded
and kept in memory while being accessed.  
You could run a simple 640x480x8 terminal with
16MB, but I'm not sure how much can be done with
only 8MB.

The ATI video cards come with a wide range of
memory depending mainly on the age of the card.
Others have reported trying the Xpert98 but I don't
remember whether the reports were good or bad.

Russ