[PATCH 2/3 v2] mm: Reorg code to allow i_mmap_mutex acquisition tobe done by caller of page_referenced & try_to_unmap

[Tim Chen]

We reorganize the page_referenced and try_to_unmap code to determine
explicitly if mapping->i_mmap_mutex needs to be acquired.  This allows
us to acquire the mutex for multiple pages in batch. We can call 
__page_referenced or __try_to_unmap with the mutex already acquired so
the mutex doesn't have to be acquired multiple times.

Tim

---
Signed-off-by: Tim Chen <tim.c.chen@xxxxxxxxxxxxxxx>
---
diff --git a/include/linux/rmap.h b/include/linux/rmap.h
index fd07c45..f1320b1 100644
--- a/include/linux/rmap.h
+++ b/include/linux/rmap.h
@@ -156,8 +156,11 @@ static inline void page_dup_rmap(struct page *page)
 /*
  * Called from mm/vmscan.c to handle paging out
  */
-int page_referenced(struct page *, int is_locked,
-			struct mem_cgroup *memcg, unsigned long *vm_flags);
+int needs_page_mmap_mutex(struct page *page);
+int page_referenced(struct page *, int is_locked, struct mem_cgroup *memcg,
+				unsigned long *vm_flags);
+int __page_referenced(struct page *, int is_locked, struct mem_cgroup *memcg,
+				unsigned long *vm_flags);
 int page_referenced_one(struct page *, struct vm_area_struct *,
 	unsigned long address, unsigned int *mapcount, unsigned long *vm_flags);
 
@@ -176,6 +179,7 @@ enum ttu_flags {
 bool is_vma_temporary_stack(struct vm_area_struct *vma);
 
 int try_to_unmap(struct page *, enum ttu_flags flags);
+int __try_to_unmap(struct page *, enum ttu_flags flags);
 int try_to_unmap_one(struct page *, struct vm_area_struct *,
 			unsigned long address, enum ttu_flags flags);
 
diff --git a/mm/rmap.c b/mm/rmap.c
index 5b5ad58..8be1799 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -843,8 +843,7 @@ static int page_referenced_file(struct page *page,
 	 * so we can safely take mapping->i_mmap_mutex.
 	 */
 	BUG_ON(!PageLocked(page));
-
-	mutex_lock(&mapping->i_mmap_mutex);
+	BUG_ON(!mutex_is_locked(&mapping->i_mmap_mutex));
 
 	/*
 	 * i_mmap_mutex does not stabilize mapcount at all, but mapcount
@@ -869,21 +868,15 @@ static int page_referenced_file(struct page *page,
 			break;
 	}
 
-	mutex_unlock(&mapping->i_mmap_mutex);
 	return referenced;
 }
 
-/**
- * page_referenced - test if the page was referenced
- * @page: the page to test
- * @is_locked: caller holds lock on the page
- * @memcg: target memory cgroup
- * @vm_flags: collect encountered vma->vm_flags who actually referenced the page
- *
- * Quick test_and_clear_referenced for all mappings to a page,
- * returns the number of ptes which referenced the page.
- */
-int page_referenced(struct page *page,
+int needs_page_mmap_mutex(struct page *page)
+{
+	return page->mapping && !PageKsm(page) && !PageAnon(page);
+}
+
+int __page_referenced(struct page *page,
 		    int is_locked,
 		    struct mem_cgroup *memcg,
 		    unsigned long *vm_flags)
@@ -919,6 +912,32 @@ out:
 	return referenced;
 }
 
+/**
+ * page_referenced - test if the page was referenced
+ * @page: the page to test
+ * @is_locked: caller holds lock on the page
+ * @memcg: target memory cgroup
+ * @vm_flags: collect encountered vma->vm_flags who actually referenced the page
+ *
+ * Quick test_and_clear_referenced for all mappings to a page,
+ * returns the number of ptes which referenced the page.
+ */
+int page_referenced(struct page *page,
+		    int is_locked,
+		    struct mem_cgroup *memcg,
+		    unsigned long *vm_flags)
+{
+	int result, needs_lock;
+
+	needs_lock = needs_page_mmap_mutex(page);
+	if (needs_lock)
+		mutex_lock(&page->mapping->i_mmap_mutex);
+	result = __page_referenced(page, is_locked, memcg, vm_flags);
+	if (needs_lock)
+		mutex_unlock(&page->mapping->i_mmap_mutex);
+	return result;
+}
+
 static int page_mkclean_one(struct page *page, struct vm_area_struct *vma,
 			    unsigned long address)
 {
@@ -1560,7 +1579,7 @@ static int try_to_unmap_file(struct page *page, enum ttu_flags flags)
 	unsigned long max_nl_size = 0;
 	unsigned int mapcount;
 
-	mutex_lock(&mapping->i_mmap_mutex);
+	BUG_ON(!mutex_is_locked(&mapping->i_mmap_mutex));
 	vma_prio_tree_foreach(vma, &iter, &mapping->i_mmap, pgoff, pgoff) {
 		unsigned long address = vma_address(page, vma);
 		if (address == -EFAULT)
@@ -1640,7 +1659,24 @@ static int try_to_unmap_file(struct page *page, enum ttu_flags flags)
 	list_for_each_entry(vma, &mapping->i_mmap_nonlinear, shared.vm_set.list)
 		vma->vm_private_data = NULL;
 out:
-	mutex_unlock(&mapping->i_mmap_mutex);
+	return ret;
+}
+
+int __try_to_unmap(struct page *page, enum ttu_flags flags)
+{
+	int ret;
+
+	BUG_ON(!PageLocked(page));
+	VM_BUG_ON(!PageHuge(page) && PageTransHuge(page));
+
+	if (unlikely(PageKsm(page)))
+		ret = try_to_unmap_ksm(page, flags);
+	else if (PageAnon(page))
+		ret = try_to_unmap_anon(page, flags);
+	else
+		ret = try_to_unmap_file(page, flags);
+	if (ret != SWAP_MLOCK && !page_mapped(page))
+		ret = SWAP_SUCCESS;
 	return ret;
 }
 
@@ -1660,20 +1696,27 @@ out:
  */
 int try_to_unmap(struct page *page, enum ttu_flags flags)
 {
-	int ret;
+	int result, needs_lock;
+
+	needs_lock = needs_page_mmap_mutex(page);
+	if (needs_lock)
+		mutex_lock(&page->mapping->i_mmap_mutex);
+	result = __try_to_unmap(page, flags);
+	if (needs_lock)
+		mutex_unlock(&page->mapping->i_mmap_mutex);
+	return result;
+}
 
-	BUG_ON(!PageLocked(page));
-	VM_BUG_ON(!PageHuge(page) && PageTransHuge(page));
+static int __try_to_munlock(struct page *page)
+{
+	VM_BUG_ON(!PageLocked(page) || PageLRU(page));
 
 	if (unlikely(PageKsm(page)))
-		ret = try_to_unmap_ksm(page, flags);
+		return try_to_unmap_ksm(page, TTU_MUNLOCK);
 	else if (PageAnon(page))
-		ret = try_to_unmap_anon(page, flags);
+		return try_to_unmap_anon(page, TTU_MUNLOCK);
 	else
-		ret = try_to_unmap_file(page, flags);
-	if (ret != SWAP_MLOCK && !page_mapped(page))
-		ret = SWAP_SUCCESS;
-	return ret;
+		return try_to_unmap_file(page, TTU_MUNLOCK);
 }
 
 /**
@@ -1693,14 +1736,15 @@ int try_to_unmap(struct page *page, enum ttu_flags flags)
  */
 int try_to_munlock(struct page *page)
 {
-	VM_BUG_ON(!PageLocked(page) || PageLRU(page));
-
-	if (unlikely(PageKsm(page)))
-		return try_to_unmap_ksm(page, TTU_MUNLOCK);
-	else if (PageAnon(page))
-		return try_to_unmap_anon(page, TTU_MUNLOCK);
-	else
-		return try_to_unmap_file(page, TTU_MUNLOCK);
+	int result, needs_lock;
+
+	needs_lock = needs_page_mmap_mutex(page);
+	if (needs_lock)
+		mutex_lock(&page->mapping->i_mmap_mutex);
+	result = __try_to_munlock(page);
+	if (needs_lock)
+		mutex_unlock(&page->mapping->i_mmap_mutex);
+	return result;
 }
 
 void __put_anon_vma(struct anon_vma *anon_vma)






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