[PATCH 6/6] sysctl: Add global tunable mt_page_copy

[Anshuman Khandual <khandual@linux.vnet.ibm.com>]

From: Zi Yan <ziy@nvidia.com>

A new global sysctl tunable 'mt_page_copy' is added which will override
syscall specific requests and enable multi threaded page copy during
all migrations on the system. This tunable is disabled by default.

Signed-off-by: Zi Yan <zi.yan@cs.rutgers.edu>
Signed-off-by: Anshuman Khandual <khandual@linux.vnet.ibm.com>
---
 kernel/sysctl.c | 10 ++++++++++
 mm/migrate.c    | 14 ++++++++++++++
 2 files changed, 24 insertions(+)

diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 1aea594..e5f7ca9 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -98,6 +98,7 @@
 #if defined(CONFIG_SYSCTL)
 
 /* External variables not in a header file. */
+extern int mt_page_copy;
 extern int suid_dumpable;
 #ifdef CONFIG_COREDUMP
 extern int core_uses_pid;
@@ -1346,6 +1347,15 @@ static struct ctl_table vm_table[] = {
 		.proc_handler   = &hugetlb_mempolicy_sysctl_handler,
 	},
 #endif
+	{
+		.procname	= "mt_page_copy",
+		.data		= &mt_page_copy,
+		.maxlen		= sizeof(mt_page_copy),
+		.mode		= 0644,
+		.proc_handler	= proc_dointvec,
+		.extra1		= &zero,
+		.extra2		= &one,
+	},
 	 {
 		.procname	= "hugetlb_shm_group",
 		.data		= &sysctl_hugetlb_shm_group,
diff --git a/mm/migrate.c b/mm/migrate.c
index 660c4b2..75b6d7a 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -48,6 +48,8 @@
 
 #include "internal.h"
 
+int mt_page_copy;
+
 /*
  * migrate_prep() needs to be called before we start compiling a list of pages
  * to be migrated using isolate_lru_page(). If scheduling work on other CPUs is
@@ -611,6 +613,9 @@ static void copy_huge_page(struct page *dst, struct page *src,
 		nr_pages = hpage_nr_pages(src);
 	}
 
+	if (mt_page_copy)
+		mode |= MIGRATE_MT;
+
 	if (mode & MIGRATE_MT)
 		rc = copy_pages_mthread(dst, src, nr_pages);
 
@@ -629,6 +634,9 @@ void migrate_page_copy(struct page *newpage, struct page *page,
 {
 	int cpupid;
 
+	if (mt_page_copy)
+		mode |= MIGRATE_MT;
+
 	if (PageHuge(page) || PageTransHuge(page)) {
 		copy_huge_page(newpage, page, mode);
 	} else {
@@ -695,6 +703,12 @@ void migrate_page_copy(struct page *newpage, struct page *page,
 }
 EXPORT_SYMBOL(migrate_page_copy);
 
+static int __init mt_page_copy_init(void)
+{
+	mt_page_copy = 0;
+	return 0;
+}
+subsys_initcall(mt_page_copy_init);
 /************************************************************
  *                    Migration functions
  ***********************************************************/
-- 
2.9.3