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Re: [Xen-devel] [RFC PATCH v3 01/24] NUMA: Make number of NUMA nodes configurable

On 19/07/17 09:17, Wei Liu wrote:
On Tue, Jul 18, 2017 at 06:52:11PM +0100, Julien Grall wrote:

On 18/07/17 16:29, Wei Liu wrote:
On Tue, Jul 18, 2017 at 05:11:23PM +0530, vijay.kilari@xxxxxxxxx wrote:
From: Vijaya Kumar K <Vijaya.Kumar@xxxxxxxxxx>

Introduce NR_NODES config option to specify number
of NUMA nodes supported. By default value is set at
64 for x86 and 8 for arm. Dropped NODES_SHIFT macro.

Also move NR_NODE_MEMBLKS from asm-x86/acpi.h to xen/numa.h

Signed-off-by: Vijaya Kumar K <Vijaya.Kumar@xxxxxxxxxx>
 xen/arch/Kconfig           | 7 +++++++
 xen/include/asm-x86/acpi.h | 1 -
 xen/include/asm-x86/numa.h | 2 --
 xen/include/xen/config.h   | 1 +
 xen/include/xen/numa.h     | 7 ++-----
 5 files changed, 10 insertions(+), 8 deletions(-)

diff --git a/xen/arch/Kconfig b/xen/arch/Kconfig
index cf0acb7..9c2a4e2 100644
--- a/xen/arch/Kconfig
+++ b/xen/arch/Kconfig
@@ -6,3 +6,10 @@ config NR_CPUS
        default "128" if ARM
          Specifies the maximum number of physical CPUs which Xen will support.
+config NR_NODES
+       int "Maximum number of NUMA nodes"
+       default "64" if X86
+       default "8" if ARM
+       ---help---
+         Specifies the maximum number of NUMA nodes which Xen will support.

Since this can now be specified by user but the definition of
NUMA_NO_NODE is  not changed, I think you need to sanitise the value
provided somewhere.

Maybe introduce a build time check? There are some examples in tree. See

You can do bound-checking in Kconfig:

range 1 254

Oh, good to know. Yes this is the way to go.

(Not directed to you Wei :))

Actually looking again at Xen, we are moving away from a power of 2. So what is the rationale behind that? Have you looked at why describing the number of nodes in term of power of 2 was chosen?


Julien Grall

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