Use the helper for the checks.  Rename "check_mapping" into "zap_mapping"
because "check_mapping" looks like a bool but in fact it stores the mapping
itself.  When it's set, we check the mapping (it must be non-NULL).  When it's
cleared we skip the check, which works like the old way.

Move the duplicated comments to the helper too.

Signed-off-by: Peter Xu <peterx@redhat.com>
---
 include/linux/mm.h | 15 ++++++++++++++-
 mm/memory.c        | 29 ++++++-----------------------
 2 files changed, 20 insertions(+), 24 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 69259229f090..81e402a5fbc9 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h

@@ -1720,10 +1720,23 @@ extern void user_shm_unlock(size_t, struct ucounts *);
  * Parameter block passed down to zap_pte_range in exceptional cases.
  */
 struct zap_details {
-	struct address_space *check_mapping;	/* Check page->mapping if set */
+	struct address_space *zap_mapping;	/* Check page->mapping if set */
 	struct page *single_page;		/* Locked page to be unmapped */
 };
 
+/*
+ * We set details->zap_mappings when we want to unmap shared but keep private
+ * pages. Return true if skip zapping this page, false otherwise.
+ */
+static inline bool
+zap_skip_check_mapping(struct zap_details *details, struct page *page)
+{
+	if (!details || !page)
+		return false;
+
+	return details->zap_mapping != page_rmapping(page);

+}
+
 struct page *vm_normal_page(struct vm_area_struct *vma, unsigned long addr,
 			     pte_t pte);
 struct page *vm_normal_page_pmd(struct vm_area_struct *vma, unsigned long addr,

diff --git a/mm/memory.c b/mm/memory.c
index 6bba3b9fef7c..e5ee8399d270 100644
--- a/mm/memory.c
+++ b/mm/memory.c

@@ -1333,16 +1333,8 @@ static unsigned long zap_pte_range(struct mmu_gather *tlb,
 			struct page *page;
 
 			page = vm_normal_page(vma, addr, ptent);
-			if (unlikely(details) && page) {
-				/*
-				 * unmap_shared_mapping_pages() wants to
-				 * invalidate cache without truncating:
-				 * unmap shared but keep private pages.
-				 */
-				if (details->check_mapping &&
-				    details->check_mapping != page_rmapping(page))
-					continue;
-			}
+			if (unlikely(zap_skip_check_mapping(details, page)))
+				continue;

 			ptent = ptep_get_and_clear_full(mm, addr, pte,
 							tlb->fullmm);
 			tlb_remove_tlb_entry(tlb, pte, addr);

@@ -1375,17 +1367,8 @@ static unsigned long zap_pte_range(struct mmu_gather *tlb,
 		    is_device_exclusive_entry(entry)) {
 			struct page *page = pfn_swap_entry_to_page(entry);
 
-			if (unlikely(details && details->check_mapping)) {
-				/*
-				 * unmap_shared_mapping_pages() wants to
-				 * invalidate cache without truncating:
-				 * unmap shared but keep private pages.
-				 */
-				if (details->check_mapping !=
-				    page_rmapping(page))
-					continue;
-			}
-
+			if (unlikely(zap_skip_check_mapping(details, page)))
+				continue;
 			pte_clear_not_present_full(mm, addr, pte, tlb->fullmm);
 			rss[mm_counter(page)]--;
 

@@ -3368,7 +3351,7 @@ void unmap_mapping_page(struct page *page)
 	first_index = page->index;
 	last_index = page->index + thp_nr_pages(page) - 1;
 
-	details.check_mapping = mapping;
+	details.zap_mapping = mapping;
 	details.single_page = page;
 
 	i_mmap_lock_write(mapping);

@@ -3396,7 +3379,7 @@ void unmap_mapping_pages(struct address_space *mapping, pgoff_t start,
 	pgoff_t	first_index = start, last_index = start + nr - 1;
 	struct zap_details details = { };
 
-	details.check_mapping = even_cows ? NULL : mapping;
+	details.zap_mapping = even_cows ? NULL : mapping;
 	if (last_index < first_index)
 		last_index = ULONG_MAX;