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

[Anshuman Khandual]

From: Zi Yan <z...@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....@cs.rutgers.edu>
Signed-off-by: Anshuman Khandual <khand...@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