[PATCH v12 31/31] mm: Add a speculative page fault switch in sysctl

[Laurent Dufour]

This allows to turn on/off the use of the speculative page fault handler.

By default it's turned on.

Signed-off-by: Laurent Dufour <ldufour at linux.ibm.com>
---
 include/linux/mm.h | 3 +++
 kernel/sysctl.c    | 9 +++++++++
 mm/memory.c        | 3 +++
 3 files changed, 15 insertions(+)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index ec609cbad25a..f5bf13a2197a 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1531,6 +1531,7 @@ extern vm_fault_t handle_mm_fault(struct vm_area_struct *vma,
 			unsigned long address, unsigned int flags);
 
 #ifdef CONFIG_SPECULATIVE_PAGE_FAULT
+extern int sysctl_speculative_page_fault;
 extern vm_fault_t __handle_speculative_fault(struct mm_struct *mm,
 					     unsigned long address,
 					     unsigned int flags);
@@ -1538,6 +1539,8 @@ static inline vm_fault_t handle_speculative_fault(struct mm_struct *mm,
 						  unsigned long address,
 						  unsigned int flags)
 {
+	if (unlikely(!sysctl_speculative_page_fault))
+		return VM_FAULT_RETRY;
 	/*
 	 * Try speculative page fault for multithreaded user space task only.
 	 */
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 9df14b07a488..3a712e52c14a 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -1295,6 +1295,15 @@ static struct ctl_table vm_table[] = {
 		.extra1		= &zero,
 		.extra2		= &two,
 	},
+#ifdef CONFIG_SPECULATIVE_PAGE_FAULT
+	{
+		.procname	= "speculative_page_fault",
+		.data		= &sysctl_speculative_page_fault,
+		.maxlen		= sizeof(sysctl_speculative_page_fault),
+		.mode		= 0644,
+		.proc_handler	= proc_dointvec,
+	},
+#endif
 	{
 		.procname	= "panic_on_oom",
 		.data		= &sysctl_panic_on_oom,
diff --git a/mm/memory.c b/mm/memory.c
index c65e8011d285..a12a60891350 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -83,6 +83,9 @@
 
 #define CREATE_TRACE_POINTS
 #include <trace/events/pagefault.h>
+#ifdef CONFIG_SPECULATIVE_PAGE_FAULT
+int sysctl_speculative_page_fault = 1;
+#endif
 
 #if defined(LAST_CPUPID_NOT_IN_PAGE_FLAGS) && !defined(CONFIG_COMPILE_TEST)
 #warning Unfortunate NUMA and NUMA Balancing config, growing page-frame for last_cpupid.
-- 
2.21.0