linux-kernel - [PATCH] mm: make falutaround selectable

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Date:   Mon, 19 Jul 2021 10:08:45 +0900
From:   Chanho Min <chanho.min@....com>
To:     Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org
Cc:     linux-kernel@...r.kernel.org,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Gunho Lee <gunho.lee@....com>, Juneho Choi <juno.choi@....com>,
        Inkyu Hwang <inkyu.hwang@....com>,
        Chanho Min <chanho.min@....com>
Subject: [PATCH] mm: make falutaround selectable

While faultaround can have performance gains, on certain platform it
increases pss and causes swap to occur more frequently. This patch allows
to unselect faultaround on platforms that do not want this behavior.

Signed-off-by: Chanho Min <chanho.min@....com>
---
 mm/Kconfig  | 6 ++++++
 mm/memory.c | 4 ++++
 2 files changed, 10 insertions(+)

diff --git a/mm/Kconfig b/mm/Kconfig
index 39a6a977537d..8f834386e7f3 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -750,4 +750,10 @@ config ARCH_HAS_PTE_SPECIAL
 config ARCH_HAS_HUGEPD
 	bool
 
+config FAULT_AROUND
+	bool "Enable fault around"
+	default y
+	help
+	 This option enables fault around. If say N, fault_around_bytes set to PAGE_SIZE
+	 and disables fault around.
 endmenu
diff --git a/mm/memory.c b/mm/memory.c
index 10d2e4734e82..0bb037265dda 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3500,7 +3500,11 @@ vm_fault_t finish_fault(struct vm_fault *vmf)
 }
 
 static unsigned long fault_around_bytes __read_mostly =
+#ifdef CONFIG_FAULT_AROUND
 	rounddown_pow_of_two(65536);
+#else
+	PAGE_SIZE;
+#endif
 
 #ifdef CONFIG_DEBUG_FS
 static int fault_around_bytes_get(void *data, u64 *val)
-- 
2.17.1