[PATCH] Revert "mm: munlock: manual pte walk in fast path instead offollow_page_mask()"

[Vlastimil Babka]

This reverts commit 7a8010cd36273ff5f6fea5201ef9232f30cebbd9 for testing.
---
 include/linux/mm.h |  12 +++---
 mm/mlock.c         | 110 +++++++++++++++--------------------------------------
 2 files changed, 37 insertions(+), 85 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 8b6e55e..e9bab9c 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -630,12 +630,12 @@ static inline enum zone_type page_zonenum(const struct page *page)
 #endif
 
 /*
- * The identification function is mainly used by the buddy allocator for
- * determining if two pages could be buddies. We are not really identifying
- * the zone since we could be using the section number id if we do not have
- * node id available in page flags.
- * We only guarantee that it will return the same value for two combinable
- * pages in a zone.
+ * The identification function is only used by the buddy allocator for
+ * determining if two pages could be buddies. We are not really
+ * identifying a zone since we could be using a the section number
+ * id if we have not node id available in page flags.
+ * We guarantee only that it will return the same value for two
+ * combinable pages in a zone.
  */
 static inline int page_zone_id(struct page *page)
 {
diff --git a/mm/mlock.c b/mm/mlock.c
index d638026..19a934d 100644
--- a/mm/mlock.c
+++ b/mm/mlock.c
@@ -280,7 +280,8 @@ static void __putback_lru_fast(struct pagevec *pvec, int pgrescued)
  * The second phase finishes the munlock only for pages where isolation
  * succeeded.
  *
- * Note that the pagevec may be modified during the process.
+ * Note that pvec is modified during the process. Before returning
+ * pagevec_reinit() is called on it.
  */
 static void __munlock_pagevec(struct pagevec *pvec, struct zone *zone)
 {
@@ -355,60 +356,8 @@ skip_munlock:
 	 */
 	if (pagevec_count(&pvec_putback))
 		__putback_lru_fast(&pvec_putback, pgrescued);
-}
-
-/*
- * Fill up pagevec for __munlock_pagevec using pte walk
- *
- * The function expects that the struct page corresponding to @start address is
- * a non-TPH page already pinned and in the @pvec, and that it belongs to @zone.
- *
- * The rest of @pvec is filled by subsequent pages within the same pmd and same
- * zone, as long as the pte's are present and vm_normal_page() succeeds. These
- * pages also get pinned.
- *
- * Returns the address of the next page that should be scanned. This equals
- * @start + PAGE_SIZE when no page could be added by the pte walk.
- */
-static unsigned long __munlock_pagevec_fill(struct pagevec *pvec,
-		struct vm_area_struct *vma, int zoneid,	unsigned long start,
-		unsigned long end)
-{
-	pte_t *pte;
-	spinlock_t *ptl;
-
-	/*
-	 * Initialize pte walk starting at the already pinned page where we
-	 * are sure that there is a pte.
-	 */
-	pte = get_locked_pte(vma->vm_mm, start,	&ptl);
-	end = min(end, pmd_addr_end(start, end));
-
-	/* The page next to the pinned page is the first we will try to get */
-	start += PAGE_SIZE;
-	while (start < end) {
-		struct page *page = NULL;
-		pte++;
-		if (pte_present(*pte))
-			page = vm_normal_page(vma, start, *pte);
-		/*
-		 * Break if page could not be obtained or the page's node+zone does not
-		 * match
-		 */
-		if (!page || page_zone_id(page) != zoneid)
-			break;
 
-		get_page(page);
-		/*
-		 * Increase the address that will be returned *before* the
-		 * eventual break due to pvec becoming full by adding the page
-		 */
-		start += PAGE_SIZE;
-		if (pagevec_add(pvec, page) == 0)
-			break;
-	}
-	pte_unmap_unlock(pte, ptl);
-	return start;
+	pagevec_reinit(pvec);
 }
 
 /*
@@ -432,16 +381,17 @@ static unsigned long __munlock_pagevec_fill(struct pagevec *pvec,
 void munlock_vma_pages_range(struct vm_area_struct *vma,
 			     unsigned long start, unsigned long end)
 {
+	struct pagevec pvec;
+	struct zone *zone = NULL;
+
+	pagevec_init(&pvec, 0);
 	vma->vm_flags &= ~VM_LOCKED;
 
 	while (start < end) {
-		struct page *page = NULL;
+		struct page *page;
 		unsigned int page_mask, page_increm;
-		struct pagevec pvec;
-		struct zone *zone;
-		int zoneid;
+		struct zone *pagezone;
 
-		pagevec_init(&pvec, 0);
 		/*
 		 * Although FOLL_DUMP is intended for get_dump_page(),
 		 * it just so happens that its special treatment of the
@@ -450,10 +400,22 @@ void munlock_vma_pages_range(struct vm_area_struct *vma,
 		 * has sneaked into the range, we won't oops here: great).
 		 */
 		page = follow_page_mask(vma, start, FOLL_GET | FOLL_DUMP,
-				&page_mask);
-
+					&page_mask);
 		if (page && !IS_ERR(page)) {
+			pagezone = page_zone(page);
+			/* The whole pagevec must be in the same zone */
+			if (pagezone != zone) {
+				if (pagevec_count(&pvec))
+					__munlock_pagevec(&pvec, zone);
+				zone = pagezone;
+			}
 			if (PageTransHuge(page)) {
+				/*
+				 * THP pages are not handled by pagevec due
+				 * to their possible split (see below).
+				 */
+				if (pagevec_count(&pvec))
+					__munlock_pagevec(&pvec, zone);
 				lock_page(page);
 				/*
 				 * Any THP page found by follow_page_mask() may
@@ -466,31 +428,21 @@ void munlock_vma_pages_range(struct vm_area_struct *vma,
 				put_page(page); /* follow_page_mask() */
 			} else {
 				/*
-				 * Non-huge pages are handled in batches via
-				 * pagevec. The pin from follow_page_mask()
-				 * prevents them from collapsing by THP.
-				 */
-				pagevec_add(&pvec, page);
-				zone = page_zone(page);
-				zoneid = page_zone_id(page);
-
-				/*
-				 * Try to fill the rest of pagevec using fast
-				 * pte walk. This will also update start to
-				 * the next page to process. Then munlock the
-				 * pagevec.
+				 * Non-huge pages are handled in batches
+				 * via pagevec. The pin from
+				 * follow_page_mask() prevents them from
+				 * collapsing by THP.
 				 */
-				start = __munlock_pagevec_fill(&pvec, vma,
-						zoneid, start, end);
-				__munlock_pagevec(&pvec, zone);
-				goto next;
+				if (pagevec_add(&pvec, page) == 0)
+					__munlock_pagevec(&pvec, zone);
 			}
 		}
 		page_increm = 1 + (~(start >> PAGE_SHIFT) & page_mask);
 		start += page_increm * PAGE_SIZE;
-next:
 		cond_resched();
 	}
+	if (pagevec_count(&pvec))
+		__munlock_pagevec(&pvec, zone);
 }
 
 /*
-- 
1.8.1.4


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