VMPLIT question

VMPLIT question

[Nishanth Aravamudan]

While building a newer kernel for a server (which had been running
2.6.12 or so), I spent some time looking for how to set the VMSPLIT
.config options. I searched in menuconfig for VMSPLIT and was given a
few responses, all similar to this:

  │ Symbol: VMSPLIT_3G [=n]
  │ Prompt: 3G/1G user/kernel split
  │   Defined at arch/i386/Kconfig:488
  │   Depends on: <choice>             

Since depending on "<choice>" is less than helpful, I did an rgrep and
found what it actually depends on:

  depends on EXPERIMENTAL && !X86_PAE
  prompt "Memory split" if EMBEDDED
  default VMSPLIT_3G

and was able to determine that I needed the patch recently submitted by
Dave Hansen to enable VMSPLIT for highmem kernels. Is there a reason
that menuconfig is not able to tell me this, i.e. this is a known
limitation of the choice syntax?

Thanks,
Nish

-- 
Nishanth Aravamudan <nacc@us.ibm.com>
IBM Linux Technology Center

Re: VMPLIT question

[Nishanth Aravamudan]

On 12.08.2006 [07:44:35 -0700], Dave Hansen wrote:
> On Fri, 2006-08-11 at 22:27 -0700, Nishanth Aravamudan wrote:
> > While building a newer kernel for a server (which had been running
> > 2.6.12 or so), I spent some time looking for how to set the VMSPLIT
> > .config options. I searched in menuconfig for VMSPLIT and was given a
> > few responses, all similar to this:
> > 
> >   â?????? Symbol: VMSPLIT_3G [=n]
> >   â?????? Prompt: 3G/1G user/kernel split
> >   â??????   Defined at arch/i386/Kconfig:488
> >   â??????   Depends on: <choice>             
> > 
> > Since depending on "<choice>" is less than helpful, I did an rgrep and
> > found what it actually depends on:
> > 
> >   depends on EXPERIMENTAL && !X86_PAE
> >   prompt "Memory split" if EMBEDDED
> >   default VMSPLIT_3G
> > 
> > and was able to determine that I needed the patch recently submitted by
> > Dave Hansen to enable VMSPLIT for highmem kernels. Is there a reason
> > that menuconfig is not able to tell me this, i.e. this is a known
> > limitation of the choice syntax?
> 
> You need to ask for help with the high-level option, not the actual
> "choice":

The "high-level option" being ...? What did you search for in menuconfig
to get the following? And, in any case, how is it useful to return a
"(null)" symbol name?

>   ??? Symbol: (null) [=y]                                                                         ???
>   ??? Prompt: Memory split                                                                        ???
>   ???   Defined at arch/i386/Kconfig:494                                                          ???
>   ???   Depends on: EXPERIMENTAL && !X86_PAE && EMBEDDED                                          ???
>   ???   Location:                                                                                 ???
>   ???     -> Processor type and features                                                          ???
>   ???   Selected by: EXPERIMENTAL && !X86_PAE && EMBEDDED && m                                    ???

Thanks,
Nish

-- 
Nishanth Aravamudan <nacc@us.ibm.com>
IBM Linux Technology Center

Re: VMPLIT question

[Dave Hansen]

On Sat, 2006-08-12 at 12:16 -0700, Nishanth Aravamudan wrote:
> > You need to ask for help with the high-level option, not the actual
> > "choice":
> 
> The "high-level option" being ...?

In menuconfig, at least:

	"Memory split (3G/1G user/kernel split)  --->"

Inside of "Processor type and features".

> What did you search for in menuconfig
> to get the following? And, in any case, how is it useful to return a
> "(null)" symbol name? 

The trouble is that the help text is associated with the top-level
"choice" Kconfig entry, not the _individual_ choices.  There is no
symbol associated with the top-level one.  It might be useful to allow
help text to be associated with individual "choice" entries, to display
that text in the high-level option, and to replace the "null" symbol
with something that says "this choice can select any of these symbols:
FOO, BAR, etc..."

I'm sure the Kconfig folks take patches. :P

-- Dave

Re: VMPLIT question

[Nishanth Aravamudan]

On 14.08.2006 [09:59:06 -0700], Dave Hansen wrote:
> On Sat, 2006-08-12 at 12:16 -0700, Nishanth Aravamudan wrote:
> > > You need to ask for help with the high-level option, not the actual
> > > "choice":
> > 
> > The "high-level option" being ...?
> 
> In menuconfig, at least:
> 
> 	"Memory split (3G/1G user/kernel split)  --->"
> 
> Inside of "Processor type and features".

I think you missed the point. If you don't know that the "Memory Split"
submenu is hidden unless you enable EMBEDDED && EXPERIMENTAL and are
!X86_PAE (the latter was the problem here, until I applied your patch),
then this is not helpful. You'll do what I did, and search for VMSPLIT
in menuconfig and get the results I pasted in my first mail, which as I
said then are less than helpful.

> > What did you search for in menuconfig to get the following? And, in
> > any case, how is it useful to return a "(null)" symbol name? 
> 
> The trouble is that the help text is associated with the top-level
> "choice" Kconfig entry, not the _individual_ choices.  There is no
> symbol associated with the top-level one.  It might be useful to allow
> help text to be associated with individual "choice" entries, to
> display that text in the high-level option, and to replace the "null"
> symbol with something that says "this choice can select any of these
> symbols: FOO, BAR, etc..."

Right, I gathered as much...

> I'm sure the Kconfig folks take patches. :P

And that's what I had Roman and Sam on the Cc, as I wanted their input
if this was a worthwhile change.

Thanks,
Nish

-- 
Nishanth Aravamudan <nacc@us.ibm.com>
IBM Linux Technology Center

Re: VMPLIT question

[Sam Ravnborg]

On Mon, Aug 14, 2006 at 10:07:18AM -0700, Nishanth Aravamudan wrote:
 
> > I'm sure the Kconfig folks take patches. :P
> 
> And that's what I had Roman and Sam on the Cc, as I wanted their input
> if this was a worthwhile change.

IMO this would be nice to have fixed - but this part of kconfig is
really Roman's area.

	Sam