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From:   Alex Shi <alex.shi@linux.alibaba.com>
To:     akpm@linux-foundation.org, mgorman@techsingularity.net,
        tj@kernel.org, hughd@google.com, khlebnikov@yandex-team.ru,
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Subject: [PATCH v19 07/20] mm/vmscan: remove unnecessary lruvec adding
Date:   Thu, 24 Sep 2020 11:28:22 +0800
Message-Id: <1600918115-22007-8-git-send-email-alex.shi@linux.alibaba.com>
In-Reply-To: <1600918115-22007-1-git-send-email-alex.shi@linux.alibaba.com>
References: <1600918115-22007-1-git-send-email-alex.shi@linux.alibaba.com>
Precedence: bulk

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 before put_page_testzero for list
integrity, otherwise:

  #0 move_pages_to_lru             #1 release_pages
  if !put_page_testzero
     			           if (put_page_testzero())
     			              !PageLRU //skip lru_lock
     SetPageLRU()
     list_add(&page->lru,)
                                         list_add(&page->lru,)

[akpm@linux-foundation.org: coding style fixes]
Signed-off-by: Alex Shi <alex.shi@linux.alibaba.com>
Acked-by: Hugh Dickins <hughd@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Tejun Heo <tj@kernel.org>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Hugh Dickins <hughd@google.com>
Cc: linux-mm@kvack.org
Cc: linux-kernel@vger.kernel.org
---
 mm/vmscan.c | 38 +++++++++++++++++++++++++-------------
 1 file changed, 25 insertions(+), 13 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 466fc3144fff..32102e5d354d 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1850,26 +1850,30 @@ 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);
 
+		/*
+		 * The SetPageLRU needs to be kept here for list integrity.
+		 * Otherwise:
+		 *   #0 move_pages_to_lru             #1 release_pages
+		 *   if !put_page_testzero
+		 *				      if (put_page_testzero())
+		 *				        !PageLRU //skip lru_lock
+		 *     SetPageLRU()
+		 *     list_add(&page->lru,)
+		 *                                        list_add(&page->lru,)
+		 */
 		SetPageLRU(page);
-		lru = page_lru(page);
 
-		nr_pages = thp_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)) {
+		if (unlikely(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);
@@ -1877,11 +1881,19 @@ static unsigned noinline_for_stack move_pages_to_lru(struct lruvec *lruvec,
 				spin_lock_irq(&pgdat->lru_lock);
 			} else
 				list_add(&page->lru, &pages_to_free);
-		} else {
-			nr_moved += nr_pages;
-			if (PageActive(page))
-				workingset_age_nonresident(lruvec, nr_pages);
+
+			continue;
 		}
+
+		lruvec = mem_cgroup_page_lruvec(page, pgdat);
+		lru = page_lru(page);
+		nr_pages = thp_nr_pages(page);
+
+		update_lru_size(lruvec, lru, page_zonenum(page), nr_pages);
+		list_add(&page->lru, &lruvec->lists[lru]);
+		nr_moved += nr_pages;
+		if (PageActive(page))
+			workingset_age_nonresident(lruvec, nr_pages);
 	}
 
 	/*
-- 
1.8.3.1