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[v3,3/8] arm64: mm: Implement arch_wants_old_prefaulted_pte()

Message ID 20210114175934.13070-4-will@kernel.org (mailing list archive)
State New, archived
Headers show
Series Create 'old' ptes for faultaround mappings on arm64 with hardware access flag | expand

Commit Message

Will Deacon Jan. 14, 2021, 5:59 p.m. UTC
On CPUs with hardware AF/DBM, initialising prefaulted PTEs as 'old'
improves vmscan behaviour and does not appear to introduce any overhead

Implement arch_wants_old_prefaulted_pte() to return 'true' if we detect
hardware access flag support at runtime. This can be extended in future
based on MIDR matching if necessary.

Cc: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Will Deacon <will@kernel.org>
 arch/arm64/include/asm/pgtable.h | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)
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diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
index 501562793ce2..e17b96d0e4b5 100644
--- a/arch/arm64/include/asm/pgtable.h
+++ b/arch/arm64/include/asm/pgtable.h
@@ -980,7 +980,17 @@  static inline bool arch_faults_on_old_pte(void)
 	return !cpu_has_hw_af();
-#define arch_faults_on_old_pte arch_faults_on_old_pte
+#define arch_faults_on_old_pte		arch_faults_on_old_pte
+ * Experimentally, it's cheap to set the access flag in hardware and we
+ * benefit from prefaulting mappings as 'old' to start with.
+ */
+static inline bool arch_wants_old_prefaulted_pte(void)
+	return !arch_faults_on_old_pte();
+#define arch_wants_old_prefaulted_pte	arch_wants_old_prefaulted_pte
 #endif /* !__ASSEMBLY__ */