[PATCH v6 14/18] arm64/mm: Implement new [get_and_]clear_full_ptes() batch APIs

[Ryan Roberts]

Optimize the contpte implementation to fix some of the
exit/munmap/dontneed performance regression introduced by the initial
contpte commit. Subsequent patches will solve it entirely.

During exit(), munmap() or madvise(MADV_DONTNEED), mappings must be
cleared. Previously this was done 1 PTE at a time. But the core-mm
supports batched clear via the new [get_and_]clear_full_ptes() APIs. So
let's implement those APIs and for fully covered contpte mappings, we no
longer need to unfold the contpte. This significantly reduces unfolding
operations, reducing the number of tlbis that must be issued.

Tested-by: John Hubbard <jhubbard at nvidia.com>
Signed-off-by: Ryan Roberts <ryan.roberts at arm.com>
---
 arch/arm64/include/asm/pgtable.h | 67 ++++++++++++++++++++++++++++++++
 arch/arm64/mm/contpte.c          | 17 ++++++++
 2 files changed, 84 insertions(+)

diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
index 8643227c318b..a8f1a35e3086 100644
--- a/arch/arm64/include/asm/pgtable.h
+++ b/arch/arm64/include/asm/pgtable.h
@@ -965,6 +965,37 @@ static inline pte_t __ptep_get_and_clear(struct mm_struct *mm,
 	return pte;
 }
 
+static inline void __clear_full_ptes(struct mm_struct *mm, unsigned long addr,
+				pte_t *ptep, unsigned int nr, int full)
+{
+	for (;;) {
+		__ptep_get_and_clear(mm, addr, ptep);
+		if (--nr == 0)
+			break;
+		ptep++;
+		addr += PAGE_SIZE;
+	}
+}
+
+static inline pte_t __get_and_clear_full_ptes(struct mm_struct *mm,
+				unsigned long addr, pte_t *ptep,
+				unsigned int nr, int full)
+{
+	pte_t pte, tmp_pte;
+
+	pte = __ptep_get_and_clear(mm, addr, ptep);
+	while (--nr) {
+		ptep++;
+		addr += PAGE_SIZE;
+		tmp_pte = __ptep_get_and_clear(mm, addr, ptep);
+		if (pte_dirty(tmp_pte))
+			pte = pte_mkdirty(pte);
+		if (pte_young(tmp_pte))
+			pte = pte_mkyoung(pte);
+	}
+	return pte;
+}
+
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
 #define __HAVE_ARCH_PMDP_HUGE_GET_AND_CLEAR
 static inline pmd_t pmdp_huge_get_and_clear(struct mm_struct *mm,
@@ -1160,6 +1191,11 @@ extern pte_t contpte_ptep_get(pte_t *ptep, pte_t orig_pte);
 extern pte_t contpte_ptep_get_lockless(pte_t *orig_ptep);
 extern void contpte_set_ptes(struct mm_struct *mm, unsigned long addr,
 				pte_t *ptep, pte_t pte, unsigned int nr);
+extern void contpte_clear_full_ptes(struct mm_struct *mm, unsigned long addr,
+				pte_t *ptep, unsigned int nr, int full);
+extern pte_t contpte_get_and_clear_full_ptes(struct mm_struct *mm,
+				unsigned long addr, pte_t *ptep,
+				unsigned int nr, int full);
 extern int contpte_ptep_test_and_clear_young(struct vm_area_struct *vma,
 				unsigned long addr, pte_t *ptep);
 extern int contpte_ptep_clear_flush_young(struct vm_area_struct *vma,
@@ -1253,6 +1289,35 @@ static inline void pte_clear(struct mm_struct *mm,
 	__pte_clear(mm, addr, ptep);
 }
 
+#define clear_full_ptes clear_full_ptes
+static inline void clear_full_ptes(struct mm_struct *mm, unsigned long addr,
+				pte_t *ptep, unsigned int nr, int full)
+{
+	if (likely(nr == 1)) {
+		contpte_try_unfold(mm, addr, ptep, __ptep_get(ptep));
+		__clear_full_ptes(mm, addr, ptep, nr, full);
+	} else {
+		contpte_clear_full_ptes(mm, addr, ptep, nr, full);
+	}
+}
+
+#define get_and_clear_full_ptes get_and_clear_full_ptes
+static inline pte_t get_and_clear_full_ptes(struct mm_struct *mm,
+				unsigned long addr, pte_t *ptep,
+				unsigned int nr, int full)
+{
+	pte_t pte;
+
+	if (likely(nr == 1)) {
+		contpte_try_unfold(mm, addr, ptep, __ptep_get(ptep));
+		pte = __get_and_clear_full_ptes(mm, addr, ptep, nr, full);
+	} else {
+		pte = contpte_get_and_clear_full_ptes(mm, addr, ptep, nr, full);
+	}
+
+	return pte;
+}
+
 #define __HAVE_ARCH_PTEP_GET_AND_CLEAR
 static inline pte_t ptep_get_and_clear(struct mm_struct *mm,
 				unsigned long addr, pte_t *ptep)
@@ -1337,6 +1402,8 @@ static inline int ptep_set_access_flags(struct vm_area_struct *vma,
 #define set_pte					__set_pte
 #define set_ptes				__set_ptes
 #define pte_clear				__pte_clear
+#define clear_full_ptes				__clear_full_ptes
+#define get_and_clear_full_ptes			__get_and_clear_full_ptes
 #define __HAVE_ARCH_PTEP_GET_AND_CLEAR
 #define ptep_get_and_clear			__ptep_get_and_clear
 #define __HAVE_ARCH_PTEP_TEST_AND_CLEAR_YOUNG
diff --git a/arch/arm64/mm/contpte.c b/arch/arm64/mm/contpte.c
index bedb58524535..50e0173dc5ee 100644
--- a/arch/arm64/mm/contpte.c
+++ b/arch/arm64/mm/contpte.c
@@ -212,6 +212,23 @@ void contpte_set_ptes(struct mm_struct *mm, unsigned long addr,
 }
 EXPORT_SYMBOL(contpte_set_ptes);
 
+void contpte_clear_full_ptes(struct mm_struct *mm, unsigned long addr,
+				pte_t *ptep, unsigned int nr, int full)
+{
+	contpte_try_unfold_partial(mm, addr, ptep, nr);
+	__clear_full_ptes(mm, addr, ptep, nr, full);
+}
+EXPORT_SYMBOL(contpte_clear_full_ptes);
+
+pte_t contpte_get_and_clear_full_ptes(struct mm_struct *mm,
+				unsigned long addr, pte_t *ptep,
+				unsigned int nr, int full)
+{
+	contpte_try_unfold_partial(mm, addr, ptep, nr);
+	return __get_and_clear_full_ptes(mm, addr, ptep, nr, full);
+}
+EXPORT_SYMBOL(contpte_get_and_clear_full_ptes);
+
 int contpte_ptep_test_and_clear_young(struct vm_area_struct *vma,
 					unsigned long addr, pte_t *ptep)
 {
-- 
2.25.1