[PATCH v6 01/10] mm/vmscan: remove unnecessary lruvec adding

[Alex Shi]

We don't have to add a freeable page into lru and then remove from it.
This change saves a couple of actions and makes the moving more clear.

The SetPageLRU needs to be kept here for list intergrity. Otherwise:

    #0 mave_pages_to_lru                #1 release_pages
                                        if (put_page_testzero())
    if (put_page_testzero())
	                                    !PageLRU //skip lru_lock
                                                list_add(&page->lru,);
    else
        list_add(&page->lru,) //corrupt

Signed-off-by: Alex Shi <alex.shi@xxxxxxxxxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: yun.wang@xxxxxxxxxxxxxxxxx
Cc: linux-mm@xxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
---
 mm/vmscan.c | 16 +++++++---------
 1 file changed, 7 insertions(+), 9 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 74e8edce83ca..7de2bb126b40 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1852,26 +1852,18 @@ static unsigned noinline_for_stack move_pages_to_lru(struct lruvec *lruvec,
 	while (!list_empty(list)) {
 		page = lru_to_page(list);
 		VM_BUG_ON_PAGE(PageLRU(page), page);
+		list_del(&page->lru);
 		if (unlikely(!page_evictable(page))) {
-			list_del(&page->lru);
 			spin_unlock_irq(&pgdat->lru_lock);
 			putback_lru_page(page);
 			spin_lock_irq(&pgdat->lru_lock);
 			continue;
 		}
-		lruvec = mem_cgroup_page_lruvec(page, pgdat);
-
 		SetPageLRU(page);
-		lru = page_lru(page);
-
-		nr_pages = hpage_nr_pages(page);
-		update_lru_size(lruvec, lru, page_zonenum(page), nr_pages);
-		list_move(&page->lru, &lruvec->lists[lru]);
 
 		if (put_page_testzero(page)) {
 			__ClearPageLRU(page);
 			__ClearPageActive(page);
-			del_page_from_lru_list(page, lruvec, lru);
 
 			if (unlikely(PageCompound(page))) {
 				spin_unlock_irq(&pgdat->lru_lock);
@@ -1880,6 +1872,12 @@ static unsigned noinline_for_stack move_pages_to_lru(struct lruvec *lruvec,
 			} else
 				list_add(&page->lru, &pages_to_free);
 		} else {
+			lruvec = mem_cgroup_page_lruvec(page, pgdat);
+			lru = page_lru(page);
+			nr_pages = hpage_nr_pages(page);
+
+			update_lru_size(lruvec, lru, page_zonenum(page), nr_pages);
+			list_add(&page->lru, &lruvec->lists[lru]);
 			nr_moved += nr_pages;
 		}
 	}
-- 
1.8.3.1