[PATCH 4/5] mm: Introduce zap_details.zap_flags

[Peter Xu]

Instead of trying to introduce one variable for every new zap_details fields,
let's introduce a flag so that it can start to encode true/false informations.

Let's start to use this flag first to clean up the only check_mapping variable.
Firstly, the name "check_mapping" implies this is a "boolean", but actually it
stores the mapping inside, just in a way that it won't be set if we don't want
to check the mapping.

To make things clearer, introduce the 1st zap flag ZAP_FLAG_CHECK_MAPPING, so
that we only check against the mapping if this bit set.  At the same time, we
can rename check_mapping into zap_mapping and set it always.

Since at it, introduce another helper zap_check_mapping_skip() and use it in
zap_pte_range() properly.

Some old comments have been removed in zap_pte_range() because they're
duplicated, and since now we're with ZAP_FLAG_CHECK_MAPPING flag, it'll be very
easy to grep this information by simply grepping the flag.

It'll also make life easier when we want to e.g. pass in zap_flags into the
callers like unmap_mapping_pages() (instead of adding new booleans besides the
even_cows parameter).

Signed-off-by: Peter Xu <peterx@xxxxxxxxxx>
---
 include/linux/mm.h | 19 ++++++++++++++++++-
 mm/memory.c        | 34 ++++++++++------------------------
 2 files changed, 28 insertions(+), 25 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 69259229f090..fcbc1c4f8e8e 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1716,14 +1716,31 @@ static inline bool can_do_mlock(void) { return false; }
 extern int user_shm_lock(size_t, struct ucounts *);
 extern void user_shm_unlock(size_t, struct ucounts *);
 
+/* Whether to check page->mapping when zapping */
+#define  ZAP_FLAG_CHECK_MAPPING             BIT(0)
+
 /*
  * 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;
 	struct page *single_page;		/* Locked page to be unmapped */
+	unsigned long zap_flags;
 };
 
+/* 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;
+
+	if (!(details->zap_flags & ZAP_FLAG_CHECK_MAPPING))
+		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 3b860f6a51ac..05ccacda4fe9 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)]--;
 
@@ -3369,8 +3352,9 @@ 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;
+	details.zap_flags = ZAP_FLAG_CHECK_MAPPING;
 
 	i_mmap_lock_write(mapping);
 	if (unlikely(!RB_EMPTY_ROOT(&mapping->i_mmap.rb_root)))
@@ -3395,9 +3379,11 @@ 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 = { };
+	struct zap_details details = { .zap_mapping = mapping };
+
+	if (!even_cows)
+		details.zap_flags |= ZAP_FLAG_CHECK_MAPPING;
 
-	details.check_mapping = even_cows ? NULL : mapping;
 	if (last_index < first_index)
 		last_index = ULONG_MAX;
 
-- 
2.31.1