2020-10-29 10:47:34

by Alex Shi

Subject: [PATCH v20 07/20] mm/vmscan: remove unnecessary lruvec adding

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,)

[[email protected]: coding style fixes]
Signed-off-by: Alex Shi <[email protected]>
Acked-by: Hugh Dickins <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Johannes Weiner <[email protected]>
Cc: Tejun Heo <[email protected]>
Cc: Matthew Wilcox <[email protected]>
Cc: Hugh Dickins <[email protected]>
Cc: [email protected]
Cc: [email protected]
---
mm/vmscan.c | 38 +++++++++++++++++++++++++-------------
1 file changed, 25 insertions(+), 13 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 1b8f0e059767..6c6965cbbdef 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1852,26 +1852,30 @@ 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);
@@ -1879,11 +1883,19 @@ 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

2020-11-02 14:24:21

by Johannes Weiner

Subject: Re: [PATCH v20 07/20] mm/vmscan: remove unnecessary lruvec adding

On Thu, Oct 29, 2020 at 06:44:52PM +0800, Alex Shi wrote:
> 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,)
>
> [[email protected]: coding style fixes]
> Signed-off-by: Alex Shi <[email protected]>
> Acked-by: Hugh Dickins <[email protected]>
> Cc: Andrew Morton <[email protected]>
> Cc: Johannes Weiner <[email protected]>
> Cc: Tejun Heo <[email protected]>
> Cc: Matthew Wilcox <[email protected]>
> Cc: Hugh Dickins <[email protected]>
> Cc: [email protected]
> Cc: [email protected]

Acked-by: Johannes Weiner <[email protected]>