[PATCH 4/6] mm/migrate: Add new migrate mode MIGRATE_MT

[Anshuman Khandual]

From: Zi Yan <z...@nvidia.com>

This change adds a new migration mode called MIGRATE_MT to enable multi
threaded page copy implementation inside copy_huge_page() function by
selectively calling copy_pages_mthread() when requested. But it still
falls back using the regular page copy mechanism instead the previous
multi threaded attempt fails. It also attempts multi threaded copy for
regular pages.

Signed-off-by: Zi Yan <zi....@cs.rutgers.edu>
Signed-off-by: Anshuman Khandual <khand...@linux.vnet.ibm.com>
---
 include/linux/migrate_mode.h |  1 +
 mm/migrate.c                 | 25 ++++++++++++++++++-------
 2 files changed, 19 insertions(+), 7 deletions(-)

diff --git a/include/linux/migrate_mode.h b/include/linux/migrate_mode.h
index 89c1700..d344ad6 100644
--- a/include/linux/migrate_mode.h
+++ b/include/linux/migrate_mode.h
@@ -12,6 +12,7 @@ enum migrate_mode {
        MIGRATE_SYNC_LIGHT      = 1<<1,
        MIGRATE_SYNC            = 1<<2,
        MIGRATE_ST              = 1<<3,
+       MIGRATE_MT              = 1<<4,
 };
 
 #endif         /* MIGRATE_MODE_H_INCLUDED */
diff --git a/mm/migrate.c b/mm/migrate.c
index 63c3682..6ac3572 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -594,6 +594,7 @@ static void copy_huge_page(struct page *dst, struct page 
*src,
 {
        int i;
        int nr_pages;
+       int rc = -EFAULT;
 
        if (PageHuge(src)) {
                /* hugetlbfs page */
@@ -610,10 +611,14 @@ static void copy_huge_page(struct page *dst, struct page 
*src,
                nr_pages = hpage_nr_pages(src);
        }
 
-       for (i = 0; i < nr_pages; i++) {
-               cond_resched();
-               copy_highpage(dst + i, src + i);
-       }
+       if (mode & MIGRATE_MT)
+               rc = copy_pages_mthread(dst, src, nr_pages);
+
+       if (rc)
+               for (i = 0; i < nr_pages; i++) {
+                       cond_resched();
+                       copy_highpage(dst + i, src + i);
+               }
 }
 
 /*
@@ -624,10 +629,16 @@ void migrate_page_copy(struct page *newpage, struct page 
*page,
 {
        int cpupid;
 
-       if (PageHuge(page) || PageTransHuge(page))
+       if (PageHuge(page) || PageTransHuge(page)) {
                copy_huge_page(newpage, page, mode);
-       else
-               copy_highpage(newpage, page);
+       } else {
+               if (mode & MIGRATE_MT) {
+                       if (copy_pages_mthread(newpage, page, 1))
+                               copy_highpage(newpage, page);
+               } else {
+                       copy_highpage(newpage, page);
+               }
+       }
 
        if (PageError(page))
                SetPageError(newpage);
-- 
2.9.3