[PATCH 5/9] mm/rmap: extend rmap_walk_xxx() to cope with different cases

[Joonsoo Kim <iamjoonsoo.kim@lge.com>]

There are a lot of common parts in traversing functions, but there are
also a little of uncommon parts in it. By assigning proper function
pointer on each rmap_walker_control, we can handle these difference
correctly.

Following are differences we should handle.

1. difference of lock function in anon mapping case
2. nonlinear handling in file mapping case
3. prechecked condition:
	checking memcg in page_referenced(),
	checking VM_SHARE in page_mkclean()
	checking temporary vma in try_to_unmap()
4. exit condition:
	checking page_mapped() in try_to_unmap()

So, in this patch, I introduce 4 function pointers to
handle above differences.

Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>

diff --git a/include/linux/rmap.h b/include/linux/rmap.h
index 0f65686..58624b4 100644
--- a/include/linux/rmap.h
+++ b/include/linux/rmap.h
@@ -239,6 +239,12 @@ struct rmap_walk_control {
 	int (*main)(struct page *, struct vm_area_struct *,
 					unsigned long, void *);
 	void *arg;	/* argument to main function */
+	int (*main_done)(struct page *page);	/* check exit condition */
+	int (*file_nonlinear)(struct page *, struct address_space *,
+					struct vm_area_struct *vma);
+	struct anon_vma *(*anon_lock)(struct page *);
+	int (*vma_skip)(struct vm_area_struct *, void *);
+	void *skip_arg;	/* argument to vma_skip function */
 };
 
 /*
diff --git a/mm/ksm.c b/mm/ksm.c
index c42ec30..0aa6e09 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -2032,12 +2032,19 @@ again:
 			if ((rmap_item->mm == vma->vm_mm) == search_new_forks)
 				continue;
 
+			if (rwc->vma_skip && rwc->vma_skip(vma, rwc->skip_arg))
+				continue;
+
 			ret = rwc->main(page, vma,
 					rmap_item->address, rwc->arg);
 			if (ret != SWAP_AGAIN) {
 				anon_vma_unlock_read(anon_vma);
 				goto out;
 			}
+			if (rwc->main_done && rwc->main_done(page)) {
+				anon_vma_unlock_read(anon_vma);
+				goto out;
+			}
 		}
 		anon_vma_unlock_read(anon_vma);
 	}
diff --git a/mm/rmap.c b/mm/rmap.c
index 5933488..5dad5dd 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1683,10 +1683,14 @@ void __put_anon_vma(struct anon_vma *anon_vma)
 }
 
 #ifdef CONFIG_MIGRATION
-static struct anon_vma *rmap_walk_anon_lock(struct page *page)
+static struct anon_vma *rmap_walk_anon_lock(struct page *page,
+					struct rmap_walk_control *rwc)
 {
 	struct anon_vma *anon_vma;
 
+	if (rwc->anon_lock)
+		return rwc->anon_lock(page);
+
 	/*
 	 * Note: remove_migration_ptes() cannot use page_lock_anon_vma_read()
 	 * because that depends on page_mapped(); but not all its usages
@@ -1712,16 +1716,22 @@ static int rmap_walk_anon(struct page *page, struct rmap_walk_control *rwc)
 	struct anon_vma_chain *avc;
 	int ret = SWAP_AGAIN;
 
-	anon_vma = rmap_walk_anon_lock(page);
+	anon_vma = rmap_walk_anon_lock(page, rwc);
 	if (!anon_vma)
 		return ret;
 
 	anon_vma_interval_tree_foreach(avc, &anon_vma->rb_root, pgoff, pgoff) {
 		struct vm_area_struct *vma = avc->vma;
 		unsigned long address = vma_address(page, vma);
+
+		if (rwc->vma_skip && rwc->vma_skip(vma, rwc->skip_arg))
+			continue;
+
 		ret = rwc->main(page, vma, address, rwc->arg);
 		if (ret != SWAP_AGAIN)
 			break;
+		if (rwc->main_done && rwc->main_done(page))
+			break;
 	}
 	anon_vma_unlock_read(anon_vma);
 	return ret;
@@ -1743,15 +1753,26 @@ static int rmap_walk_file(struct page *page, struct rmap_walk_control *rwc)
 	mutex_lock(&mapping->i_mmap_mutex);
 	vma_interval_tree_foreach(vma, &mapping->i_mmap, pgoff, pgoff) {
 		unsigned long address = vma_address(page, vma);
+
+		if (rwc->vma_skip && rwc->vma_skip(vma, rwc->skip_arg))
+			continue;
+
 		ret = rwc->main(page, vma, address, rwc->arg);
 		if (ret != SWAP_AGAIN)
-			break;
+			goto done;
+		if (rwc->main_done && rwc->main_done(page))
+			goto done;
 	}
-	/*
-	 * No nonlinear handling: being always shared, nonlinear vmas
-	 * never contain migration ptes.  Decide what to do about this
-	 * limitation to linear when we need rmap_walk() on nonlinear.
-	 */
+
+	if (!rwc->file_nonlinear)
+		goto done;
+
+	if (list_empty(&mapping->i_mmap_nonlinear))
+		goto done;
+
+	ret = rwc->file_nonlinear(page, mapping, vma);
+
+done:
 	mutex_unlock(&mapping->i_mmap_mutex);
 	return ret;
 }
-- 
1.7.9.5