[PATCH] x86_64: Reserve SRAT hotadd memory on x86-64

From: Keith Mannthey, Andi Kleen

Implement memory hotadd without sparsemem. The memory in the SRAT
hotadd area is just preserved instead and can be activated later.

There are a few restrictions:
- Only one continuous hotadd area allowed per node

The main problem is dealing with the many buggy SRAT tables
that are out there. The strategy here is to reject anything
suspicious.

Originally from Keith Mannthey, with several hacks and changes by AK
and also contributions from Andrew Morton

[ TBD: Problems pointed out by KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>:

 1) Goto's rebuild_zonelist patch will not work if CONFIG_MEMORY_HOTPLUG=n.

    Rebuilding zonelist is necessary when the system has just memory <
    4G at boot, and hot add memory > 4G.  because x86_64 has DMA32,
    ZONE_NORAML is not included into zonelist at boot time if system
    doesn't have memory >4G at boot.

    [AK: should just force the higher zones at boot time when SRAT tells us]

 2) zone and node's spanned_pages and present_pages are not incremented.
    They should be.

    For example, our server (ia64/Fujitsu PrimeQuest) can equip memory
    from 4G to 1T(maybe 2T in future), and SRAT will *always* say we have
    possible 1T +memory.  (Microsoft requires "write all possible memory
    in SRAT") When we reserve memmap for possible 1T memory, Linux will
    not work well in +minimum 4G configuraion ;)

    [AK: needs limiting to 5-10% of max memory]
 ]

Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 5 insertions, 0 deletions

diff --git a/Documentation/x86_64/boot-options.txt b/Documentation/x86_64/boot-options.txt
index 1921353259ae..f2cd6ef53ff3 100644
--- a/Documentation/x86_64/boot-options.txt
+++ b/Documentation/x86_64/boot-options.txt
@@ -151,6 +151,11 @@ NUMA
 
   numa=fake=X   Fake X nodes and ignore NUMA setup of the actual machine.
 
+  numa=hotadd=percent
+                Only allow hotadd memory to preallocate page structures upto
+                percent of already available memory.
+                numa=hotadd=0 will disable hotadd memory.
+
 ACPI
 
   acpi=off      Don't enable ACPI