[RFT PATCH] riscv: mremap speedup - enable HAVE_MOVE_PUD and HAVE_MOVE_PMD

Jisheng Zhang jszhang3 at mail.ustc.edu.cn
Fri Apr 16 17:37:22 BST 2021

From: Jisheng Zhang <jszhang at kernel.org>

HAVE_MOVE_PUD enables remapping pages at the PUD level if both the source
and destination addresses are PUD-aligned.
HAVE_MOVE_PMD does similar speedup on the PMD level.

With HAVE_MOVE_PUD enabled, there is about a 143x improvement on qemu
With HAVE_MOVE_PMD enabled, there is about a 5x improvement on qemu

Signed-off-by: Jisheng Zhang <jszhang at kernel.org>
Hi all,

After reading the risc-v privileged spec, I think it's safe to support
the HAVE_MOVE_PUD and HAVE_MOVE_PMD optimization on riscv. The patch passed
the mremap_test on QEMU. However this can't be tested on real HW due to lack
of HW boards, this is the reason why I mark this patch as RFT. I hope I can
buy a sipeed Allwiner D1 SoC powered SBC soon, at least I can test
HAVE_MOVE_PMD. Helping me to test on real HW is appreciated!


 arch/riscv/Kconfig               |  2 ++
 arch/riscv/include/asm/pgtable.h | 12 ++++++++++++
 2 files changed, 14 insertions(+)

diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index e8074d248457..37660de68b00 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -80,6 +80,8 @@ config RISCV
+	select HAVE_MOVE_PMD
+	select HAVE_MOVE_PUD
 	select HAVE_PCI
diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pgtable.h
index ebf817c1bdf4..287733b95d10 100644
--- a/arch/riscv/include/asm/pgtable.h
+++ b/arch/riscv/include/asm/pgtable.h
@@ -360,6 +360,18 @@ static inline void set_pte_at(struct mm_struct *mm,
 	set_pte(ptep, pteval);
+static inline void set_pmd_at(struct mm_struct *mm, unsigned long addr,
+			      pmd_t *pmdp, pmd_t pmd)
+	set_pmd(pmdp, pmd);
+static inline void set_pud_at(struct mm_struct *mm, unsigned long addr,
+			      pud_t *pudp, pud_t pud)
+	set_pud(pudp, pud);
 static inline void pte_clear(struct mm_struct *mm,
 	unsigned long addr, pte_t *ptep)

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