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From: Will Deacon <will@kernel.org>
To: linux-kernel@vger.kernel.org
Cc: kernel-team@android.com, Jan Kara <jack@suse.cz>,
	Minchan Kim <minchan@kernel.org>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Hugh Dickins <hughd@google.com>,
	linux-mm@kvack.org, Vinayak Menon <vinmenon@codeaurora.org>,
	"Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Will Deacon <will@kernel.org>,
	linux-arm-kernel@lists.infradead.org
Subject: [PATCH v2 3/3] arm64: mm: Implement arch_wants_old_prefaulted_pte()
Date: Fri,  8 Jan 2021 17:15:17 +0000	[thread overview]
Message-ID: <20210108171517.5290-4-will@kernel.org> (raw)
In-Reply-To: <20210108171517.5290-1-will@kernel.org>

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(-)

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__ */
 
-- 
2.29.2.729.g45daf8777d-goog


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WARNING: multiple messages have this Message-ID (diff)
From: Will Deacon <will@kernel.org>
To: linux-kernel@vger.kernel.org
Cc: linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org,
	Will Deacon <will@kernel.org>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Jan Kara <jack@suse.cz>, Minchan Kim <minchan@kernel.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	"Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Vinayak Menon <vinmenon@codeaurora.org>,
	Hugh Dickins <hughd@google.com>,
	kernel-team@android.com
Subject: [PATCH v2 3/3] arm64: mm: Implement arch_wants_old_prefaulted_pte()
Date: Fri,  8 Jan 2021 17:15:17 +0000	[thread overview]
Message-ID: <20210108171517.5290-4-will@kernel.org> (raw)
In-Reply-To: <20210108171517.5290-1-will@kernel.org>

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(-)

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__ */
 
-- 
2.29.2.729.g45daf8777d-goog



  parent reply	other threads:[~2021-01-08 17:19 UTC|newest]

Thread overview: 38+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-01-08 17:15 [PATCH v2 0/3] Create 'old' ptes for faultaround mappings on arm64 with hardware access flag Will Deacon
2021-01-08 17:15 ` Will Deacon
2021-01-08 17:15 ` [PATCH v2 1/3] mm: Cleanup faultaround and finish_fault() codepaths Will Deacon
2021-01-08 17:15   ` Will Deacon
2021-01-11 14:26   ` Kirill A. Shutemov
2021-01-11 14:26     ` Kirill A. Shutemov
2021-01-11 14:27     ` Will Deacon
2021-01-11 14:27       ` Will Deacon
2021-01-08 17:15 ` [PATCH v2 2/3] mm: Allow architectures to request 'old' entries when prefaulting Will Deacon
2021-01-08 17:15   ` Will Deacon
2021-01-11 14:25   ` Kirill A. Shutemov
2021-01-11 14:25     ` Kirill A. Shutemov
2021-01-11 14:37     ` Will Deacon
2021-01-11 14:37       ` Will Deacon
2021-01-11 14:47       ` Kirill A. Shutemov
2021-01-11 14:47         ` Kirill A. Shutemov
2021-01-08 17:15 ` Will Deacon [this message]
2021-01-08 17:15   ` [PATCH v2 3/3] arm64: mm: Implement arch_wants_old_prefaulted_pte() Will Deacon
2021-01-08 19:34 ` [PATCH v2 0/3] Create 'old' ptes for faultaround mappings on arm64 with hardware access flag Linus Torvalds
2021-01-08 19:34   ` Linus Torvalds
2021-01-08 19:42   ` Linus Torvalds
2021-01-08 19:42     ` Linus Torvalds
2021-01-11 14:01     ` Will Deacon
2021-01-11 14:01       ` Will Deacon
2021-01-11 13:30   ` Will Deacon
2021-01-11 13:30     ` Will Deacon
2021-01-11 21:03     ` Hugh Dickins
2021-01-11 21:03       ` Hugh Dickins
2021-01-12 21:46       ` Will Deacon
2021-01-12 21:46         ` Will Deacon
2021-01-11 14:24   ` Kirill A. Shutemov
2021-01-11 14:24     ` Kirill A. Shutemov
2021-01-11 19:25     ` Linus Torvalds
2021-01-11 19:25       ` Linus Torvalds
2021-01-12 21:47       ` Will Deacon
2021-01-12 21:47         ` Will Deacon
2021-01-12 21:55         ` Linus Torvalds
2021-01-12 21:55           ` Linus Torvalds

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