[PATCH v20 13/20] mm/mlock: remove lru_lock on TestClearPageMlocked

[Alex Shi]

In the func munlock_vma_page, comments mentained lru_lock needed for
serialization with split_huge_pages. But the page must be PageLocked
as well as pages in split_huge_page series funcs. Thus the PageLocked
is enough to serialize both funcs.

Further more, Hugh Dickins pointed: before splitting in
split_huge_page_to_list, the page was unmap_page() to remove pmd/ptes
which protect the page from munlock. Thus, no needs to guard
__split_huge_page_tail for mlock clean, just keep the lru_lock there for
isolation purpose.

LKP found a preempt issue on __mod_zone_page_state which need change
to mod_zone_page_state. Thanks!

Signed-off-by: Alex Shi <alex.shi@xxxxxxxxxxxxxxxxx>
Acked-by: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: linux-mm@xxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
---
 mm/mlock.c | 26 +++++---------------------
 1 file changed, 5 insertions(+), 21 deletions(-)

diff --git a/mm/mlock.c b/mm/mlock.c
index 884b1216da6a..796c726a0407 100644
--- a/mm/mlock.c
+++ b/mm/mlock.c
@@ -187,40 +187,24 @@ static void __munlock_isolation_failed(struct page *page)
 unsigned int munlock_vma_page(struct page *page)
 {
 	int nr_pages;
-	pg_data_t *pgdat = page_pgdat(page);
 
 	/* For try_to_munlock() and to serialize with page migration */
 	BUG_ON(!PageLocked(page));
-
 	VM_BUG_ON_PAGE(PageTail(page), page);
 
-	/*
-	 * Serialize with any parallel __split_huge_page_refcount() which
-	 * might otherwise copy PageMlocked to part of the tail pages before
-	 * we clear it in the head page. It also stabilizes thp_nr_pages().
-	 */
-	spin_lock_irq(&pgdat->lru_lock);
-
 	if (!TestClearPageMlocked(page)) {
 		/* Potentially, PTE-mapped THP: do not skip the rest PTEs */
-		nr_pages = 1;
-		goto unlock_out;
+		return 0;
 	}
 
 	nr_pages = thp_nr_pages(page);
-	__mod_zone_page_state(page_zone(page), NR_MLOCK, -nr_pages);
+	mod_zone_page_state(page_zone(page), NR_MLOCK, -nr_pages);
 
-	if (__munlock_isolate_lru_page(page, true)) {
-		spin_unlock_irq(&pgdat->lru_lock);
+	if (!isolate_lru_page(page))
 		__munlock_isolated_page(page);
-		goto out;
-	}
-	__munlock_isolation_failed(page);
-
-unlock_out:
-	spin_unlock_irq(&pgdat->lru_lock);
+	else
+		__munlock_isolation_failed(page);
 
-out:
 	return nr_pages - 1;
 }
 
-- 
1.8.3.1