[PATCH v6 3/4] mm/memory.c: Add memory read privilege on page fault handling

[Bibo Mao]

Here add pte_sw_mkyoung function to make page readable on MIPS
platform during page fault handling. This patch improves page
fault latency about 10% on my MIPS machine with lmbench
lat_pagefault case.

It is noop function on other arches, there is no negative
influence on those architectures.

Signed-off-by: Bibo Mao <maob...@loongson.cn>
---
 arch/mips/include/asm/pgtable.h |  2 ++
 include/asm-generic/pgtable.h   | 16 ++++++++++++++++
 mm/memory.c                     |  3 +++
 3 files changed, 21 insertions(+)

diff --git a/arch/mips/include/asm/pgtable.h b/arch/mips/include/asm/pgtable.h
index d2004b5..0743087 100644
--- a/arch/mips/include/asm/pgtable.h
+++ b/arch/mips/include/asm/pgtable.h
@@ -414,6 +414,8 @@ static inline pte_t pte_mkyoung(pte_t pte)
        return pte;
 }
 
+#define pte_sw_mkyoung pte_mkyoung
+
 #ifdef CONFIG_MIPS_HUGE_TLB_SUPPORT
 static inline int pte_huge(pte_t pte)  { return pte_val(pte) & _PAGE_HUGE; }
 
diff --git a/include/asm-generic/pgtable.h b/include/asm-generic/pgtable.h
index fa5c73f..b5278ec 100644
--- a/include/asm-generic/pgtable.h
+++ b/include/asm-generic/pgtable.h
@@ -244,6 +244,22 @@ static inline void ptep_set_wrprotect(struct mm_struct 
*mm, unsigned long addres
 }
 #endif
 
+/*
+ * On some architectures hardware does not set page access bit when accessing
+ * memory page, it is responsibilty of software setting this bit. It brings
+ * out extra page fault penalty to track page access bit. For optimization page
+ * access bit can be set during all page fault flow on these arches.
+ * To be differentiate with macro pte_mkyoung, this macro is used on platforms
+ * where software maintains page access bit.
+ */
+#ifndef pte_sw_mkyoung
+static inline pte_t pte_sw_mkyoung(pte_t pte)
+{
+       return pte;
+}
+#define pte_sw_mkyoung pte_sw_mkyoung
+#endif
+
 #ifndef pte_savedwrite
 #define pte_savedwrite pte_write
 #endif
diff --git a/mm/memory.c b/mm/memory.c
index 8bb31c4..c7c8960 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -2704,6 +2704,7 @@ static vm_fault_t wp_page_copy(struct vm_fault *vmf)
                }
                flush_cache_page(vma, vmf->address, pte_pfn(vmf->orig_pte));
                entry = mk_pte(new_page, vma->vm_page_prot);
+               entry = pte_sw_mkyoung(entry);
                entry = maybe_mkwrite(pte_mkdirty(entry), vma);
                /*
                 * Clear the pte entry and flush it first, before updating the
@@ -3378,6 +3379,7 @@ static vm_fault_t do_anonymous_page(struct vm_fault *vmf)
        __SetPageUptodate(page);
 
        entry = mk_pte(page, vma->vm_page_prot);
+       entry = pte_sw_mkyoung(entry);
        if (vma->vm_flags & VM_WRITE)
                entry = pte_mkwrite(pte_mkdirty(entry));
 
@@ -3660,6 +3662,7 @@ vm_fault_t alloc_set_pte(struct vm_fault *vmf, struct 
mem_cgroup *memcg,
 
        flush_icache_page(vma, page);
        entry = mk_pte(page, vma->vm_page_prot);
+       entry = pte_sw_mkyoung(entry);
        if (write)
                entry = maybe_mkwrite(pte_mkdirty(entry), vma);
        /* copy-on-write page */
-- 
1.8.3.1