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

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Message-Id: <20190416134522.17540-32-ldufour@linux.ibm.com>
Date:   Tue, 16 Apr 2019 15:45:22 +0200
From:   Laurent Dufour <ldufour@...ux.ibm.com>
To:     akpm@...ux-foundation.org, mhocko@...nel.org, peterz@...radead.org,
        kirill@...temov.name, ak@...ux.intel.com, dave@...olabs.net,
        jack@...e.cz, Matthew Wilcox <willy@...radead.org>,
        aneesh.kumar@...ux.ibm.com, benh@...nel.crashing.org,
        mpe@...erman.id.au, paulus@...ba.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, hpa@...or.com,
        Will Deacon <will.deacon@....com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        sergey.senozhatsky.work@...il.com,
        Andrea Arcangeli <aarcange@...hat.com>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>,
        kemi.wang@...el.com, Daniel Jordan <daniel.m.jordan@...cle.com>,
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        vinayak menon <vinayakm.list@...il.com>,
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        Haiyan Song <haiyanx.song@...el.com>,
        Balbir Singh <bsingharora@...il.com>, sj38.park@...il.com,
        Michel Lespinasse <walken@...gle.com>,
        Mike Rapoport <rppt@...ux.ibm.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        haren@...ux.vnet.ibm.com, npiggin@...il.com,
        paulmck@...ux.vnet.ibm.com, Tim Chen <tim.c.chen@...ux.intel.com>,
        linuxppc-dev@...ts.ozlabs.org, x86@...nel.org
Subject: [PATCH v12 31/31] mm: Add a speculative page fault switch in sysctl

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@...ux.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