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