2020-03-02 11:02:15

by Alex Shi

Subject: [PATCH v9 02/20] mm/memcg: fold lock_page_lru into commit_charge

As Konstantin Khlebnikov mentioned:

Also I don't like these functions:
- called lock/unlock but actually also isolates
- used just once
- pgdat evaluated twice

Cleanup and fold these functions into commit_charge. It also reduces
lock time while lrucare && !PageLRU.

Signed-off-by: Alex Shi <[email protected]>
Cc: Johannes Weiner <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Konstantin Khlebnikov <[email protected]>
Cc: Vladimir Davydov <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
---
mm/memcontrol.c | 57 ++++++++++++++++++++-------------------------------------
1 file changed, 20 insertions(+), 37 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index d09776cd6e10..875e2aebcde7 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2572,41 +2572,11 @@ static void cancel_charge(struct mem_cgroup *memcg, unsigned int nr_pages)
css_put_many(&memcg->css, nr_pages);
}

-static void lock_page_lru(struct page *page, int *isolated)
-{
- pg_data_t *pgdat = page_pgdat(page);
-
- spin_lock_irq(&pgdat->lru_lock);
- if (PageLRU(page)) {
- struct lruvec *lruvec;
-
- lruvec = mem_cgroup_page_lruvec(page, pgdat);
- ClearPageLRU(page);
- del_page_from_lru_list(page, lruvec, page_lru(page));
- *isolated = 1;
- } else
- *isolated = 0;
-}
-
-static void unlock_page_lru(struct page *page, int isolated)
-{
- pg_data_t *pgdat = page_pgdat(page);
-
- if (isolated) {
- struct lruvec *lruvec;
-
- lruvec = mem_cgroup_page_lruvec(page, pgdat);
- VM_BUG_ON_PAGE(PageLRU(page), page);
- SetPageLRU(page);
- add_page_to_lru_list(page, lruvec, page_lru(page));
- }
- spin_unlock_irq(&pgdat->lru_lock);
-}
-
static void commit_charge(struct page *page, struct mem_cgroup *memcg,
bool lrucare)
{
- int isolated;
+ struct lruvec *lruvec = NULL;
+ pg_data_t *pgdat;

VM_BUG_ON_PAGE(page->mem_cgroup, page);

@@ -2614,9 +2584,17 @@ static void commit_charge(struct page *page, struct mem_cgroup *memcg,
* In some cases, SwapCache and FUSE(splice_buf->radixtree), the page
* may already be on some other mem_cgroup's LRU. Take care of it.
*/
- if (lrucare)
- lock_page_lru(page, &isolated);
-
+ if (lrucare) {
+ pgdat = page_pgdat(page);
+ spin_lock_irq(&pgdat->lru_lock);
+
+ if (PageLRU(page)) {
+ lruvec = mem_cgroup_page_lruvec(page, pgdat);
+ ClearPageLRU(page);
+ del_page_from_lru_list(page, lruvec, page_lru(page));
+ } else
+ spin_unlock_irq(&pgdat->lru_lock);
+ }
/*
* Nobody should be changing or seriously looking at
* page->mem_cgroup at this point:
@@ -2633,8 +2611,13 @@ static void commit_charge(struct page *page, struct mem_cgroup *memcg,
*/
page->mem_cgroup = memcg;

- if (lrucare)
- unlock_page_lru(page, isolated);
+ if (lrucare && lruvec) {
+ lruvec = mem_cgroup_page_lruvec(page, pgdat);
+ VM_BUG_ON_PAGE(PageLRU(page), page);
+ SetPageLRU(page);
+ add_page_to_lru_list(page, lruvec, page_lru(page));
+ spin_unlock_irq(&pgdat->lru_lock);
+ }
}

#ifdef CONFIG_MEMCG_KMEM
--
1.8.3.1

2020-03-04 07:21:02

by Alex Shi

Subject: Re: [PATCH v9 02/20] mm/memcg: fold lock_page_lru into commit_charge

?? 2020/3/4 ????11:13, Hillf Danton д??:
>> * Nobody should be changing or seriously looking at
>> * page->mem_cgroup at this point:
>> @@ -2633,8 +2611,13 @@ static void commit_charge(struct page *page, struct mem_cgroup *memcg,
>> */
>> page->mem_cgroup = memcg;
>>
> Well it is likely to update memcg for page without lru_lock held even if
> more care is required, which is a change added in the current semantic and
> worth a line of words in log.
>

the lru_lock is guard for lru list, not for page->mem_cgroup, seem no need to highlight this point. Do we?

Thanks
Alex