MFS ROOT over 100MB

Hi,


it's possible create MFS ROOT over 100MB?
If I create MFS ROOT less then 90MB, system boot normally.
With size 90MB-100MB of MFS ROOT kernel panic with boot and
over 100MB system is rebooted in loop.


MFS ROOT image is ok (i can mount this image via mdconfig
and mount).
I'am testing this on RELENG_6_2 and RELENG_7_0.

The same problem like this:
http://lists.freebsd.org/pipermail/fr
eebsd-stable/2008-February/040626.html

Thanks,
Mira

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Miroslav Chlastak <chlastakfialka.cz> writes:

> it's possible create MFS ROOT over 100MB?
> If I create MFS ROOT less then 90MB, system boot
normally.
> With size 90MB-100MB of MFS ROOT kernel panic with boot
and
> over 100MB system is rebooted in loop.

Are you running i386 or amd64. I recall that we had a
similar problem
at work a few years ago, but only on i386.

We solved it by using geom_uzip(4) to get a smaller mfsroot
image.

-- 
Christian Laursen
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Miroslav Chlastak wrote:
> Hi,
> 
> 
> it's possible create MFS ROOT over 100MB?
> If I create MFS ROOT less then 90MB, system boot
normally.
> With size 90MB-100MB of MFS ROOT kernel panic with boot
and
> over 100MB system is rebooted in loop.
> 

I suspect that the MFS root is loaded into kenrelVM which is
a limited 
resource. in fact it must be I think because it is linked
with the 
kernel by the loader.


> 
> MFS ROOT image is ok (i can mount this image via
mdconfig and mount).
> I'am testing this on RELENG_6_2 and RELENG_7_0.
> 
> The same problem like this:
> http://lists.freebsd.org/pipermail/fr
eebsd-stable/2008-February/040626.html
> 
> Thanks,
> Mira
> 
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> To unsubscribe, send any mail to
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On Fri, Mar 28, 2008 at 1:12 PM, Julian Elischer
<julianelischer.org> wrote:
> Miroslav Chlastak wrote:
>  > Hi,
>  >
>  >
>  > it's possible create MFS ROOT over 100MB?
>  > If I create MFS ROOT less then 90MB, system boot
normally.
>  > With size 90MB-100MB of MFS ROOT kernel panic
with boot and
>  > over 100MB system is rebooted in loop.
>  >
>
>  I suspect that the MFS root is loaded into kenrelVM
which is a limited
>  resource. in fact it must be I think because it is
linked with the
>  kernel by the loader.

There isn't a lot of spare kernel virtual memory by default,
but there
are other things that are likely to be being hit first.

First, have a look at the NKPT kernel compile option.  This
is
probably what is being run into.

By default, for an i386, non-PAE kernel, the value is 30. 
This is the
initial number of page table pages that are statically
allocated for
early kernel bootup.  Once the VM system is fully up and
running, we
can allocate more.  But during early bootup, this is what we
have.

In this case, 30 page table pages, and there are 1024
entries per page
table page, with 4K per entry.  ie: 30 x 1024 x 4k = 122MB. 
If the VM
system isn't fully up and running by the time this 122MB of
kernel VM
is consumed, bad things will happen.

This is where the 90-100MB threshold in MFS root image fits
in.  While
there is 1GB of KVM available in total, the MFS image has to
fit
inside this 122MB chunk, **and** the kernel has to complete
bootstrap
with what's left.

On an i386 kernel without PAE, the KVA_PAGES option is 256. 
It is
also means 256 x 1024 x 4k = 1GB.  In theory, you could
increase the
NKPT option to close to this amount.  I don't know what the
exact
threshold is, but it'll be pretty close.

ie: you should be able to add 'options NKPT=220' to the
kernel config.
 This would let you load a mfsroot in the order of about
900MB, **IN
THEORY**.  The problem is that you'll then run into other
kernel VM
exhaustion.  It still has a total of 1GB available by
default.  This
is changeable too.

If you're trying to do a massive mfsroot, you'll probably
have to
increase KVA_PAGES too.  For example, 'options
KVA_PAGES=512' gives
you 2GB of kernel VM, and 2GB left for user processes.  You
could then
set NKPT to 300+ and easily get a 1GB mfsroot ramdisk
loaded.

For PAE, page table pages have different numbers of entries.
 You have
to double the numbers because they're in units of 512 x 4k,
or 2MB per
page table page.  So with PAE, you'd need 'options
KVA_PAGES=1024' and
'options NKPT=600' to get the same 2G/2G user/kernel split,
and have
the 1gb mfsroot image.

I hope this is helpful.  You'll need to experiment to make
this work
and not waste too much memory.  There is no way to avoid
compiling
custom kernels to do this.

>  > MFS ROOT image is ok (i can mount this image via
mdconfig and mount).
>  > I'am testing this on RELENG_6_2 and RELENG_7_0.
>  >
>  > The same problem like this:
>  > http://lists.freebsd.org/pipermail/fr
eebsd-stable/2008-February/040626.html
>  >
>  > Thanks,
>  > Mira

-- 
Peter Wemm - peterwemm.org; peterFreeBSD.org; peteryahoo-inc.com
"All of this is for nothing if we don't go to the
stars" - JMS/B5
"If Java had true garbage collection, most programs
would delete
themselves upon execution." -- Robert Sewell
**WANTED TO BUY/TRADE: Garmin Streetpilot 2650 or 2660. Not
later model! **
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Peter Wemm wrote:
> On Fri, Mar 28, 2008 at 1:12 PM, Julian Elischer
<julianelischer.org> wrote:
>> Miroslav Chlastak wrote:
>>  > Hi,
>>  >
>>  >
>>  > it's possible create MFS ROOT over 100MB?
>>  > If I create MFS ROOT less then 90MB, system
boot normally.
>>  > With size 90MB-100MB of MFS ROOT kernel panic
with boot and
>>  > over 100MB system is rebooted in loop.
>>  >
>>
>>  I suspect that the MFS root is loaded into
kenrelVM which is a limited
>>  resource. in fact it must be I think because it is
linked with the
>>  kernel by the loader.
> 
> There isn't a lot of spare kernel virtual memory by
default, but there
> are other things that are likely to be being hit
first.
> 
> First, have a look at the NKPT kernel compile option. 
This is
> probably what is being run into.
> 
> By default, for an i386, non-PAE kernel, the value is
30.  This is the
> initial number of page table pages that are statically
allocated for
> early kernel bootup.  Once the VM system is fully up
and running, we
> can allocate more.  But during early bootup, this is
what we have.
> 
> In this case, 30 page table pages, and there are 1024
entries per page
> table page, with 4K per entry.  ie: 30 x 1024 x 4k =
122MB.  If the VM
> system isn't fully up and running by the time this
122MB of kernel VM
> is consumed, bad things will happen.
> 
> This is where the 90-100MB threshold in MFS root image
fits in.  While
> there is 1GB of KVM available in total, the MFS image
has to fit
> inside this 122MB chunk, **and** the kernel has to
complete bootstrap
> with what's left.
> 
> On an i386 kernel without PAE, the KVA_PAGES option is
256.  It is
> also means 256 x 1024 x 4k = 1GB.  In theory, you could
increase the
> NKPT option to close to this amount.  I don't know what
the exact
> threshold is, but it'll be pretty close.
> 
> ie: you should be able to add 'options NKPT=220' to the
kernel config.
>  This would let you load a mfsroot in the order of
about 900MB, **IN
> THEORY**.  The problem is that you'll then run into
other kernel VM
> exhaustion.  It still has a total of 1GB available by
default.  This
> is changeable too.
> 
> If you're trying to do a massive mfsroot, you'll
probably have to
> increase KVA_PAGES too.  For example, 'options
KVA_PAGES=512' gives
> you 2GB of kernel VM, and 2GB left for user processes. 
You could then
> set NKPT to 300+ and easily get a 1GB mfsroot ramdisk
loaded.
> 
> For PAE, page table pages have different numbers of
entries.  You have
> to double the numbers because they're in units of 512 x
4k, or 2MB per
> page table page.  So with PAE, you'd need 'options
KVA_PAGES=1024' and
> 'options NKPT=600' to get the same 2G/2G user/kernel
split, and have
> the 1gb mfsroot image.
> 
> I hope this is helpful.  You'll need to experiment to
make this work
> and not waste too much memory.  There is no way to
avoid compiling
> custom kernels to do this.

You could probably write code to store the memory disk in
physical
memeory and leaqe it unmapped except when needed. With PAE
you could 
then have an 8GB ram disk. I'm told that this can be done
even without 
changing the rest of the system to use PAE.. (but that's 2nd
hand info).


>>  > MFS ROOT image is ok (i can mount this image
via mdconfig and mount).
>>  > I'am testing this on RELENG_6_2 and
RELENG_7_0.
>>  >
>>  > The same problem like this:
>>  > http://lists.freebsd.org/pipermail/fr
eebsd-stable/2008-February/040626.html
>>  >
>>  > Thanks,
>>  > Mira
> 

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