[RFC PATCH 2/7] mm: introduce CONFIG_FREE_USER_PTE

[Qi Zheng <zhengqi.arch@bytedance.com>]

This configuration variable will be used to build the code needed to
free user PTE page table pages.

The PTE page table setting and clearing functions(such as set_pte_at())
are in the architecture's files, and these functions will be hooked to
implement FREE_USER_PTE, so the architecture support is needed.

Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
---
 mm/Kconfig | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/mm/Kconfig b/mm/Kconfig
index 169e64192e48..d2a5a24cee2d 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -1130,6 +1130,17 @@ config PTE_MARKER_UFFD_WP
 	  purposes.  It is required to enable userfaultfd write protection on
 	  file-backed memory types like shmem and hugetlbfs.
 
+config ARCH_SUPPORTS_FREE_USER_PTE
+	def_bool n
+
+config FREE_USER_PTE
+	bool "Free user PTE page table pages"
+	default y
+	depends on ARCH_SUPPORTS_FREE_USER_PTE && MMU && SMP
+	help
+	  Try to free user PTE page table page when its all entries are none or
+	  mapped shared zero page.
+
 source "mm/damon/Kconfig"
 
 endmenu
-- 
2.20.1