[PATCH 2/4] Free the collapsed pages after the new THP is mapped.

[Hidetoshi Seto <seto.hidetoshi@jp.fujitsu.com>]

Free pages at once after they are replaced by new THP,
instead of freeing one by one during copy.

This change is for later patches, to allow cancel of page
collapsing.

Signed-off-by: Hidetoshi Seto <seto.hidetoshi@jp.fujitsu.com>
Signed-off-by: Jin Dongming <jin.dongming@np.css.fujitsu.com>
---
 mm/huge_memory.c |   31 +++++++++++++++++++++++++------
 1 files changed, 25 insertions(+), 6 deletions(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index e02f687..c62176a 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1704,11 +1704,10 @@ out:
 
 static void __collapse_huge_page_copy(pte_t *pte, struct page *page,
 				      struct vm_area_struct *vma,
-				      unsigned long address,
-				      spinlock_t *ptl)
+				      unsigned long address)
 {
 	pte_t *_pte;
-	for (_pte = pte; _pte < pte+HPAGE_PMD_NR; _pte++) {
+	for (_pte = pte; _pte < pte + HPAGE_PMD_NR; _pte++) {
 		pte_t pteval = *_pte;
 		struct page *src_page;
 
@@ -1720,7 +1719,28 @@ static void __collapse_huge_page_copy(pte_t *pte, struct page *page,
 			copy_user_highpage(page, src_page, address, vma);
 			VM_BUG_ON(page_mapcount(src_page) != 1);
 			VM_BUG_ON(page_count(src_page) != 2);
+		}
+
+		address += PAGE_SIZE;
+		page++;
+	}
+}
+
+static void __collapse_huge_page_free_old_pte(pte_t *pte,
+					      struct vm_area_struct *vma,
+					      unsigned long address,
+					      spinlock_t *ptl)
+{
+	pte_t *_pte;
+
+	for (_pte = pte; _pte < pte + HPAGE_PMD_NR; _pte++) {
+		pte_t pteval = *_pte;
+		struct page *src_page;
+
+		if (!pte_none(pteval)) {
+			src_page = pte_page(pteval);
 			release_pte_page(src_page);
+
 			/*
 			 * ptl mostly unnecessary, but preempt has to
 			 * be disabled to update the per-cpu stats
@@ -1736,9 +1756,7 @@ static void __collapse_huge_page_copy(pte_t *pte, struct page *page,
 			spin_unlock(ptl);
 			free_page_and_swap_cache(src_page);
 		}
-
 		address += PAGE_SIZE;
-		page++;
 	}
 }
 
@@ -1875,7 +1893,7 @@ static void collapse_huge_page(struct mm_struct *mm,
 	 */
 	lock_page_nosync(new_page);
 
-	__collapse_huge_page_copy(pte, new_page, vma, address, ptl);
+	__collapse_huge_page_copy(pte, new_page, vma, address);
 	pte_unmap(pte);
 	__SetPageUptodate(new_page);
 	pgtable = pmd_pgtable(_pmd);
@@ -1905,6 +1923,7 @@ static void collapse_huge_page(struct mm_struct *mm,
 #ifndef CONFIG_NUMA
 	*hpage = NULL;
 #endif
+	__collapse_huge_page_free_old_pte(pte, vma, address, ptl);
 	khugepaged_pages_collapsed++;
 	unlock_page(new_page);
 out_up_write:
-- 
1.7.1