[PATCH -V8 16/21] swap: Free PMD swap mapping when zap_huge_pmd()

[Huang Ying]

For a PMD swap mapping, zap_huge_pmd() will clear the PMD and call
free_swap_and_cache() to decrease the swap reference count and maybe
free or split the huge swap cluster and the THP in swap cache.

Signed-off-by: "Huang, Ying" <ying.huang@xxxxxxxxx>
Cc: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Shaohua Li <shli@xxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Minchan Kim <minchan@xxxxxxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Cc: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>
Cc: Zi Yan <zi.yan@xxxxxxxxxxxxxx>
Cc: Daniel Jordan <daniel.m.jordan@xxxxxxxxxx>
---
 mm/huge_memory.c | 32 +++++++++++++++++++++-----------
 1 file changed, 21 insertions(+), 11 deletions(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 077d569da13e..5b2eb7871cd7 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2071,7 +2071,7 @@ int zap_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
 		spin_unlock(ptl);
 		if (is_huge_zero_pmd(orig_pmd))
 			tlb_remove_page_size(tlb, pmd_page(orig_pmd), HPAGE_PMD_SIZE);
-	} else if (is_huge_zero_pmd(orig_pmd)) {
+	} else if (pmd_present(orig_pmd) && is_huge_zero_pmd(orig_pmd)) {
 		zap_deposited_table(tlb->mm, pmd);
 		spin_unlock(ptl);
 		tlb_remove_page_size(tlb, pmd_page(orig_pmd), HPAGE_PMD_SIZE);
@@ -2084,17 +2084,27 @@ int zap_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
 			page_remove_rmap(page, true);
 			VM_BUG_ON_PAGE(page_mapcount(page) < 0, page);
 			VM_BUG_ON_PAGE(!PageHead(page), page);
-		} else if (thp_migration_supported()) {
-			swp_entry_t entry;
-
-			VM_BUG_ON(!is_pmd_migration_entry(orig_pmd));
-			entry = pmd_to_swp_entry(orig_pmd);
-			page = pfn_to_page(swp_offset(entry));
+		} else {
+			swp_entry_t entry = pmd_to_swp_entry(orig_pmd);
+
+			if (thp_migration_supported() &&
+			    is_migration_entry(entry))
+				page = pfn_to_page(swp_offset(entry));
+			else if (IS_ENABLED(CONFIG_THP_SWAP) &&
+				 !non_swap_entry(entry))
+				free_swap_and_cache(entry, HPAGE_PMD_NR);
+			else {
+				WARN_ONCE(1,
+"Non present huge pmd without pmd migration or swap enabled!");
+				goto unlock;
+			}
 			flush_needed = 0;
-		} else
-			WARN_ONCE(1, "Non present huge pmd without pmd migration enabled!");
+		}
 
-		if (PageAnon(page)) {
+		if (!page) {
+			zap_deposited_table(tlb->mm, pmd);
+			add_mm_counter(tlb->mm, MM_SWAPENTS, -HPAGE_PMD_NR);
+		} else if (PageAnon(page)) {
 			zap_deposited_table(tlb->mm, pmd);
 			add_mm_counter(tlb->mm, MM_ANONPAGES, -HPAGE_PMD_NR);
 		} else {
@@ -2102,7 +2112,7 @@ int zap_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
 				zap_deposited_table(tlb->mm, pmd);
 			add_mm_counter(tlb->mm, mm_counter_file(page), -HPAGE_PMD_NR);
 		}
-
+unlock:
 		spin_unlock(ptl);
 		if (flush_needed)
 			tlb_remove_page_size(tlb, page, HPAGE_PMD_SIZE);
-- 
2.18.1