[RFC PATCH 05/25] mm: migrate: Add vm.accel_page_copy in sysfs to control page copy acceleration.

[Zi Yan]

From: Zi Yan <ziy@xxxxxxxxxx>

Since base page migration did not gain any speedup from
multi-threaded methods, we only accelerate the huge page case.

Signed-off-by: Zi Yan <ziy@xxxxxxxxxx>
---
 kernel/sysctl.c | 11 +++++++++++
 mm/migrate.c    |  6 ++++++
 2 files changed, 17 insertions(+)

diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index e5da394..3d8490e 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -101,6 +101,8 @@
 
 #if defined(CONFIG_SYSCTL)
 
+extern int accel_page_copy;
+
 /* External variables not in a header file. */
 extern int suid_dumpable;
 #ifdef CONFIG_COREDUMP
@@ -1430,6 +1432,15 @@ static struct ctl_table vm_table[] = {
 		.extra2			= &one,
 	},
 #endif
+	{
+		.procname	= "accel_page_copy",
+		.data		= &accel_page_copy,
+		.maxlen		= sizeof(accel_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 dd6ccbe..8a344e2 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -55,6 +55,8 @@
 
 #include "internal.h"
 
+int accel_page_copy = 1;
+
 /*
  * 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
@@ -589,6 +591,10 @@ static void copy_huge_page(struct page *dst, struct page *src,
 		nr_pages = hpage_nr_pages(src);
 	}
 
+	/* Try to accelerate page migration if it is not specified in mode  */
+	if (accel_page_copy)
+		mode |= MIGRATE_MT;
+
 	if (mode & MIGRATE_MT)
 		rc = copy_page_multithread(dst, src, nr_pages);
 
-- 
2.7.4