[PATCH] IA64: Sparse and Discontig Mem need NUMA

[PATCH] IA64: Sparse and Discontig Mem need NUMA

[Simon Horman]

It was pointed out to me by my colleague Yamahata-san that
neither sparse nor discontig mem compile without NUMA support.

Cc: Alex Williamson <alex.williamson@hp.com>
Cc: Isaku Yamahata <yamahata@valinux.co.jp>
Signed-off-by: Simon Horman <horms@verge.net.au>

--- 
This seems line an issue best solved by prohibiting such settings through
Kconfig. But if it is desirable for sparse and discontig memory to work
without CONFIG_NUMA let me know and I'll have a stab at it. It does seem
possible code-wise. I'm just not sure if its useful.

Index: linux-2.6/arch/ia64/Kconfig
=================================--- linux-2.6.orig/arch/ia64/Kconfig	2007-05-02 16:42:22.000000000 +0900
+++ linux-2.6/arch/ia64/Kconfig	2007-05-02 16:42:26.000000000 +0900
@@ -337,6 +337,7 @@ config ARCH_SELECT_MEMORY_MODEL
 
 config ARCH_DISCONTIGMEM_ENABLE
 	def_bool y
+	depends on NUMA
 	help
 	  Say Y to support efficient handling of discontiguous physical memory,
 	  for architectures which are either NUMA (Non-Uniform Memory Access)
@@ -345,6 +346,7 @@ config ARCH_DISCONTIGMEM_ENABLE
 
 config ARCH_FLATMEM_ENABLE
 	def_bool y
+	depends on !NUMA
 
 config ARCH_SPARSEMEM_ENABLE
 	def_bool y
@@ -356,7 +358,7 @@ config ARCH_DISCONTIGMEM_DEFAULT
 
 config NUMA
 	bool "NUMA support"
-	depends on !IA64_HP_SIM && !FLATMEM
+	depends on !IA64_HP_SIM
 	default y if IA64_SGI_SN2
 	select ACPI_NUMA if ACPI
 	help

RE: [PATCH] IA64: Sparse and Discontig Mem need NUMA

[Luck, Tony]

> This seems line an issue best solved by prohibiting such settings through
> Kconfig. But if it is desirable for sparse and discontig memory to work
> without CONFIG_NUMA let me know and I'll have a stab at it. It does seem
> possible code-wise. I'm just not sure if its useful.

I pretty sure that we used to be able to build for a DISCONTIG but
non-NUMA system ... this is a quite common case, systems with >4G
of memory put the first 2G at 0-2G, reserve the 2G-4G area for
PCI memory mapped devices (and other platform specific stuff) then
the rest of RAM is at some >4G address.  With just a 2G hole it
is possible to paper over it, but some systems put the extra
memory at much higher addresses.

But it would be nice to reduce the CONFIG maze ... so perhaps we
should ponder what overhead such a system would suffer by having
to be built as CONFIG_NUMA=y.  If this is small, then perhaps we
can simplify things.

-Tony

Re: [PATCH] IA64: Sparse and Discontig Mem need NUMA

[Simon Horman]

On Wed, May 02, 2007 at 09:22:58AM -0700, Luck, Tony wrote:
> > This seems line an issue best solved by prohibiting such settings through
> > Kconfig. But if it is desirable for sparse and discontig memory to work
> > without CONFIG_NUMA let me know and I'll have a stab at it. It does seem
> > possible code-wise. I'm just not sure if its useful.
> 
> I pretty sure that we used to be able to build for a DISCONTIG but
> non-NUMA system ... this is a quite common case, systems with >4G
> of memory put the first 2G at 0-2G, reserve the 2G-4G area for
> PCI memory mapped devices (and other platform specific stuff) then
> the rest of RAM is at some >4G address.  With just a 2G hole it
> is possible to paper over it, but some systems put the extra
> memory at much higher addresses.

I did take a look at what it would take to allow Sparse to compile
in non-NUMA. It seemed that Sparse was very much centered around NUMA
so I wondered how useful the result might be. I will take a look
into Discontig and see what is required there.

> But it would be nice to reduce the CONFIG maze ... so perhaps we
> should ponder what overhead such a system would suffer by having
> to be built as CONFIG_NUMA=y.  If this is small, then perhaps we
> can simplify things.

I guess it might be a bit tricky to measure that comprehensively.
But it would certainly make things easier. I think that the patch
I sent implements what you are suggesting, though perhaps it isn't
exactly what you had in mind.

-- 
Horms
  H: http://www.vergenet.net/~horms/
  W: http://www.valinux.co.jp/en/