[PATCH v2 3/5] mm/vmalloc.c: optimize code in decay_va_pool_node() a little bit

[Baoquan He <bhe@redhat.com>]

When purge lazily freed vmap areas, VA stored in vn->pool[] will also be
taken away into free vmap tree partially or completely accordingly, that
is done in decay_va_pool_node(). When doing that, for each pool of node,
the whole list is detached from the pool for handling. At this time,
that pool is empty. It's not necessary to update the pool size each time
when one VA is removed and addded into free vmap tree.

Here change code to update the pool size when attaching the pool back.

Signed-off-by: Baoquan He <bhe@redhat.com>
---
 mm/vmalloc.c | 23 +++++++++++------------
 1 file changed, 11 insertions(+), 12 deletions(-)

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 76ab4d3ce616..cd654cc35d2b 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -2133,7 +2133,7 @@ decay_va_pool_node(struct vmap_node *vn, bool full_decay)
 	LIST_HEAD(decay_list);
 	struct rb_root decay_root = RB_ROOT;
 	struct vmap_area *va, *nva;
-	unsigned long n_decay;
+	unsigned long n_decay, pool_len;
 	int i;
 
 	for (i = 0; i < MAX_VA_SIZE_PAGES; i++) {
@@ -2147,22 +2147,20 @@ decay_va_pool_node(struct vmap_node *vn, bool full_decay)
 		list_replace_init(&vn->pool[i].head, &tmp_list);
 		spin_unlock(&vn->pool_lock);
 
-		if (full_decay)
-			WRITE_ONCE(vn->pool[i].len, 0);
+		pool_len = n_decay = vn->pool[i].len;
+		WRITE_ONCE(vn->pool[i].len, 0);
 
 		/* Decay a pool by ~25% out of left objects. */
-		n_decay = vn->pool[i].len >> 2;
+		if (!full_decay)
+			n_decay >>= 2;
+		pool_len -= n_decay;
 
 		list_for_each_entry_safe(va, nva, &tmp_list, list) {
+			if (!n_decay--)
+				break;
+
 			list_del_init(&va->list);
 			merge_or_add_vmap_area(va, &decay_root, &decay_list);
-
-			if (!full_decay) {
-				WRITE_ONCE(vn->pool[i].len, vn->pool[i].len - 1);
-
-				if (!--n_decay)
-					break;
-			}
 		}
 
 		/*
@@ -2171,9 +2169,10 @@ decay_va_pool_node(struct vmap_node *vn, bool full_decay)
 		 * can populate the pool therefore a simple list replace
 		 * operation takes place here.
 		 */
-		if (!full_decay && !list_empty(&tmp_list)) {
+		if (!list_empty(&tmp_list)) {
 			spin_lock(&vn->pool_lock);
 			list_replace_init(&tmp_list, &vn->pool[i].head);
+			WRITE_ONCE(vn->pool[i].len, pool_len);
 			spin_unlock(&vn->pool_lock);
 		}
 	}
-- 
2.41.0