Re: [PATCH v17 00/21] per memcg lru lock

Alex Shi
2020-08-04T08:37:14Z

From 0696a2a4a8ca5e9bf62f208126ea4af7727d2edc Mon Sep 17 00:00:00 2001
From: Alex Shi <alex.shi-KPsoFbNs7GizrGE5bRqYAgC/G2K4zDHf@public.gmane.org>
Date: Sat, 25 Jul 2020 22:31:03 +0800
Subject: [PATCH 1/3] mm/mlock: remove lru_lock on TestClearPageMlocked in
munlock_vma_page

In the func munlock_vma_page, the page must be PageLocked as well as
pages in split_huge_page series funcs. Thus the PageLocked is enough
to serialize both funcs.

So we could relief the TestClearPageMlocked/hpage_nr_pages which are not
necessary under lru lock.

As to another munlock func __munlock_pagevec, which no PageLocked
protection and should remain lru protecting.

Signed-off-by: Alex Shi <alex.shi-KPsoFbNs7GizrGE5bRqYAgC/G2K4zDHf@public.gmane.org>
Cc: Kirill A. Shutemov <kirill.shutemov-VuQAYsv1563Yd54FQh9/CA@public.gmane.org>
Cc: Vlastimil Babka <vbabka-AlSwsSmVLrQ@public.gmane.org>
Cc: Andrew Morton <akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>
Cc: linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org
Cc: linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
---
mm/mlock.c | 41 +++++++++++++++--------------------------
1 file changed, 15 insertions(+), 26 deletions(-)

diff --git a/mm/mlock.c b/mm/mlock.c
index 0448409184e3..46a05e6ec5ba 100644
--- a/mm/mlock.c
+++ b/mm/mlock.c
@@ -69,9 +69,9 @@ void clear_page_mlock(struct page *page)
*
* See __pagevec_lru_add_fn for more explanation.
*/
- if (!isolate_lru_page(page)) {
+ if (!isolate_lru_page(page))
putback_lru_page(page);
- } else {
+ else {
/*
* We lost the race. the page already moved to evictable list.
*/
@@ -178,7 +178,6 @@ static void __munlock_isolation_failed(struct page *page)
unsigned int munlock_vma_page(struct page *page)
{
int nr_pages;
- struct lruvec *lruvec;

/* For try_to_munlock() and to serialize with page migration */
BUG_ON(!PageLocked(page));
@@ -186,37 +185,22 @@ unsigned int munlock_vma_page(struct page *page)
VM_BUG_ON_PAGE(PageTail(page), page);

/*
- * Serialize split tail pages in __split_huge_page_tail() 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().
- * TestClearPageLRU can't be used here to block page isolation, since
- * out of lock clear_page_mlock may interfer PageLRU/PageMlocked
- * sequence, same as __pagevec_lru_add_fn, and lead the page place to
- * wrong lru list here. So relay on PageLocked to stop lruvec change
- * in mem_cgroup_move_account().
+ * Serialize split tail pages in __split_huge_page_tail() by
+ * lock_page(); Do TestClearPageMlocked/PageLRU sequence like
+ * clear_page_mlock().
*/
- lruvec = lock_page_lruvec_irq(page);
-
- if (!TestClearPageMlocked(page)) {
+ 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);

- if (__munlock_isolate_lru_page(page, lruvec, true)) {
- unlock_page_lruvec_irq(lruvec);
+ if (!isolate_lru_page(page))
__munlock_isolated_page(page);
- goto out;
- }
- __munlock_isolation_failed(page);
-
-unlock_out:
- unlock_page_lruvec_irq(lruvec);
+ else
+ __munlock_isolation_failed(page);

-out:
return nr_pages - 1;
}

@@ -305,6 +289,11 @@ static void __munlock_pagevec(struct pagevec *pvec, struct zone *zone)

/* block memcg change in mem_cgroup_move_account */
lock_page_memcg(page);
+ /*
+ * Serialize split tail pages in __split_huge_page_tail() which
+ * might otherwise copy PageMlocked to part of the tail pages
+ * before we clear it in the head page.
+ */
lruvec = relock_page_lruvec_irq(page, lruvec);
if (TestClearPageMlocked(page)) {
/*
--
1.8.3.1