[PATCH 2/3] mm/migrate: see hole as invalid source page

[Pingfan Liu <kernelfans@xxxxxxxxx>]

MIGRATE_PFN_MIGRATE marks a valid pfn, further more, suitable to migrate.
As for hole, there is no valid pfn, not to mention migration.

Before this patch, hole has already relied on the following code to be
filtered out. Hence it is more reasonable to see hole as invalid source
page.
migrate_vma_prepare()
{
		struct page *page = migrate_pfn_to_page(migrate->src[i]);

		if (!page || (migrate->src[i] & MIGRATE_PFN_MIGRATE))
		     \_ this condition
}

Signed-off-by: Pingfan Liu <kernelfans@xxxxxxxxx>
Cc: "Jérôme Glisse" <jglisse@xxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
Cc: Jan Kara <jack@xxxxxxx>
Cc: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
To: linux-mm@xxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
---
 mm/migrate.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/mm/migrate.c b/mm/migrate.c
index c2ec614..832483f 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -2136,10 +2136,9 @@ static int migrate_vma_collect_hole(unsigned long start,
 	unsigned long addr;
 
 	for (addr = start & PAGE_MASK; addr < end; addr += PAGE_SIZE) {
-		migrate->src[migrate->npages] = MIGRATE_PFN_MIGRATE;
+		migrate->src[migrate->npages] = 0;
 		migrate->dst[migrate->npages] = 0;
 		migrate->npages++;
-		migrate->cpages++;
 	}
 
 	return 0;
@@ -2228,8 +2227,7 @@ static int migrate_vma_collect_pmd(pmd_t *pmdp,
 		pfn = pte_pfn(pte);
 
 		if (pte_none(pte)) {
-			mpfn = MIGRATE_PFN_MIGRATE;
-			migrate->cpages++;
+			mpfn = 0;
 			goto next;
 		}
 
-- 
2.7.5