linux-kernel - [RFC PATCH 2/7] mm: introduce CONFIG_FREE_USER

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Message-Id: <20220825101037.96517-3-zhengqi.arch@bytedance.com>
Date:   Thu, 25 Aug 2022 18:10:32 +0800
From:   Qi Zheng <zhengqi.arch@...edance.com>
To:     akpm@...ux-foundation.org, david@...hat.com,
        kirill.shutemov@...ux.intel.com, mika.penttila@...tfour.com,
        jgg@...dia.com, tglx@...utronix.de, willy@...radead.org
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        muchun.song@...ux.dev, Qi Zheng <zhengqi.arch@...edance.com>
Subject: [RFC PATCH 2/7] mm: introduce CONFIG_FREE_USER_PTE

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@...edance.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