Firstly, the comment in zap_pte_range() is misleading because it checks against
details rather than check_mappings, so it's against what the code did.

Meanwhile, it's confusing too on not explaining why passing in the details
pointer would mean to skip all swap entries.  New user of zap_details could
very possibly miss this fact if they don't read deep until zap_pte_range()
because there's no comment at zap_details talking about it at all, so swap
entries could be errornously skipped without being noticed.

This partly reverts 3e8715fdc03e ("mm: drop zap_details::check_swap_entries"),
but introduce ZAP_FLAG_SKIP_SWAP flag, which means the opposite of previous
"details" parameter: the caller should explicitly set this to skip swap
entries, otherwise swap entries will always be considered (which is still the
major case here).

Cc: Kirill A. Shutemov <kir...@shutemov.name>
Signed-off-by: Peter Xu <pet...@redhat.com>
---
 include/linux/mm.h | 12 ++++++++++++
 mm/memory.c        |  8 +++++---
 2 files changed, 17 insertions(+), 3 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 7ed4352ec84f..16631ee5eb9d 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1622,6 +1622,8 @@ extern void user_shm_unlock(size_t, struct user_struct *);
 
 /* Whether to check page->mapping when zapping */
 #define  ZAP_FLAG_CHECK_MAPPING             BIT(0)
+/* Whether to skip zapping swap entries */
+#define  ZAP_FLAG_SKIP_SWAP                 BIT(1)
 
 /*
  * Parameter block passed down to zap_pte_range in exceptional cases.
@@ -1644,6 +1646,16 @@ zap_check_mapping_skip(struct zap_details *details, 
struct page *page)
        return details->zap_mapping != page_rmapping(page);
 }
 
+/* Return true if skip swap entries, false otherwise */
+static inline bool
+zap_skip_swap(struct zap_details *details)
+{
+       if (!details)
+               return false;
+
+       return details->zap_flags & ZAP_FLAG_SKIP_SWAP;
+}
+
 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 20a8ba05c334..c9945f3c374d 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1262,8 +1262,7 @@ static unsigned long zap_pte_range(struct mmu_gather *tlb,
                        continue;
                }
 
-               /* If details->check_mapping, we leave swap entries. */
-               if (unlikely(details))
+               if (unlikely(zap_skip_swap(details)))
                        continue;
 
                if (!non_swap_entry(entry))
@@ -3159,7 +3158,10 @@ void unmap_mapping_pages(struct address_space *mapping, 
pgoff_t start,
                pgoff_t nr, bool even_cows)
 {
        pgoff_t first_index = start, last_index = start + nr - 1;
-       struct zap_details details = { .zap_mapping = mapping };
+       struct zap_details details = {
+               .zap_mapping = mapping,
+               .zap_flags = ZAP_FLAG_SKIP_SWAP,
+       };
 
        if (!even_cows)
                details.zap_flags |= ZAP_FLAG_CHECK_MAPPING;
-- 
2.26.2

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