On 2024/1/15 23:39, Russell King (Oracle) wrote:

quoted

On Thu, Dec 14, 2023 at 04:05:56PM -0800, Christoph Lameter (Ampere) wrote:

quoted

Index: linux/arch/arm64/Kconfig
===================================================================

--- linux.orig/arch/arm64/Kconfig
+++ linux/arch/arm64/Kconfig

@@ -1407,7 +1407,21 @@ config SCHED_SMT
   config NR_CPUS
   	int "Maximum number of CPUs (2-4096)"
   	range 2 4096

I think your mailer got to your patch and messed up the white space.
There are two spaces before each of these lines rather than the usual
one.

quoted

-	default "256"
+	default 512
+
+#
+# Determines the placement of cpumasks.
+#
+# With CPUMASK_OFFSTACK the cpumasks are dynamically allocated.
+# Useful for machines with lots of core because it avoids increasing
+# the size of many of the data structures in the kernel.
+#
+# If this is off then the cpumasks have a static sizes and are
+# embedded within data structures.
+#
+config CPUMASK_OFFSTACK
+	def_bool y
+	depends on NR_CPUS > 256

Should that be ">= 256" ?

Maybe just select CPUMASK_OFFSTACK if NR_CPUS >= 256,


But could we just make CPUMASK_OFFSTACK configurable and let user/distro
to enable it?

diff --git a/lib/Kconfig b/lib/Kconfig
index 5ddda7c2ed9b..4254be5aa843 100644
--- a/lib/Kconfig
+++ b/lib/Kconfig

@@ -535,7 +535,9 @@ config CHECK_SIGNATURE
        bool

 config CPUMASK_OFFSTACK
-       bool "Force CPU masks off stack" if DEBUG_PER_CPU_MAPS
+       bool "Force CPU masks off stack"
+       depends on SMP
+       default n