x86: add gbpages switches

These new controls toggle experimental support for a new CPU feature,
the straightforward extension of largepages from the pmd level to the
pud level, which allows 1GB (kernel) TLBs instead of 2MB TLBs.

Turn it off by default, as this code has not been tested well enough yet.

Use the CONFIG_DIRECT_GBPAGES=y .config option or gbpages on the
boot line can be used to enable it. If enabled in the .config then
nogbpages boot option disables it.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

1 files changed, 12 insertions, 0 deletions

diff --git a/arch/x86/Kconfig.debug b/arch/x86/Kconfig.debug
index 7ce8e7025661..f4413c04e687 100644
--- a/arch/x86/Kconfig.debug
+++ b/arch/x86/Kconfig.debug
@@ -76,6 +76,18 @@ config DEBUG_RODATA
           data. This is recommended so that we can catch kernel bugs sooner.
           If in doubt, say "Y".
 
+config DIRECT_GBPAGES
+        bool "Enable gbpages-mapped kernel pagetables"
+        depends on DEBUG_KERNEL && EXPERIMENTAL && X86_64
+        help
+          Enable gigabyte pages support (if the CPU supports it). This can
+          improve the kernel's performance a tiny bit by reducing TLB
+          pressure.
+
+          This is experimental code.
+
+          If in doubt, say "N".
+
 config DEBUG_RODATA_TEST
         bool "Testcase for the DEBUG_RODATA feature"
         depends on DEBUG_RODATA