Re: [PATCH v18 19/32] mm/swap.c: serialize memcg changes in pagevec_lru_move_fn
From: Alex Shi
Date: Tue Sep 22 2020 - 01:02:40 EST
在 2020/9/22 上午8:42, Hugh Dickins 写道:
> On Mon, 24 Aug 2020, Alex Shi wrote:
>
>> Hugh Dickins' found a memcg change bug on original version:
>> If we want to change the pgdat->lru_lock to memcg's lruvec lock, we have
>> to serialize mem_cgroup_move_account during pagevec_lru_move_fn. The
>> possible bad scenario would like:
>>
>> cpu 0 cpu 1
>> lruvec = mem_cgroup_page_lruvec()
>> if (!isolate_lru_page())
>> mem_cgroup_move_account
>>
>> spin_lock_irqsave(&lruvec->lru_lock <== wrong lock.
>>
>> So we need the ClearPageLRU to block isolate_lru_page(), that serializes
>
> s/the ClearPageLRU/TestClearPageLRU/
Thanks, will change it.
>
>> the memcg change. and then removing the PageLRU check in move_fn callee
>> as the consequence.
>
> Deserves another paragraph about __pagevec_lru_add():
> "__pagevec_lru_add_fn() is different from the others, because the pages
> it deals with are, by definition, not yet on the lru. TestClearPageLRU
> is not needed and would not work, so __pagevec_lru_add() goes its own way."
Thanks for comments! will add it into new commit log.
>
>>
>> Reported-by: Hugh Dickins <hughd@xxxxxxxxxx>
>
> True.
>
>> Signed-off-by: Hugh Dickins <hughd@xxxxxxxxxx>
>
> I did provide some lines, but I think it's just
> Acked-by: Hugh Dickins <hughd@xxxxxxxxxx>
> to go below your Signed-off-by.
Thanks!
>
>> Signed-off-by: Alex Shi <alex.shi@xxxxxxxxxxxxxxxxx>
>> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
>> Cc: linux-mm@xxxxxxxxx
>> Cc: linux-kernel@xxxxxxxxxxxxxxx
>> ---
>> mm/swap.c | 44 +++++++++++++++++++++++++++++++++++---------
>> 1 file changed, 35 insertions(+), 9 deletions(-)
>
> In your lruv19 branch, this patch got renamed (s/moveing/moving/):
> but I think it's better with the old name used here in v18, and without
> those mm/vmscan.c mods to check_move_unevictable_pages() tacked on:
> please move those back to 16/32, which already makes changes to vmscan.c.
>
Yes, will move that part there.
Thanks!
Alex
>>
>> diff --git a/mm/swap.c b/mm/swap.c
>> index 446ffe280809..2d9a86bf93a4 100644
>> --- a/mm/swap.c
>> +++ b/mm/swap.c
>> @@ -221,8 +221,14 @@ static void pagevec_lru_move_fn(struct pagevec *pvec,
>> spin_lock_irqsave(&pgdat->lru_lock, flags);
>> }
>>
>> + /* block memcg migration during page moving between lru */
>> + if (!TestClearPageLRU(page))
>> + continue;
>> +
>> lruvec = mem_cgroup_page_lruvec(page, pgdat);
>> (*move_fn)(page, lruvec);
>> +
>> + SetPageLRU(page);
>> }
>> if (pgdat)
>> spin_unlock_irqrestore(&pgdat->lru_lock, flags);
>> @@ -232,7 +238,7 @@ static void pagevec_lru_move_fn(struct pagevec *pvec,
>>
>> static void pagevec_move_tail_fn(struct page *page, struct lruvec *lruvec)
>> {
>> - if (PageLRU(page) && !PageUnevictable(page)) {
>> + if (!PageUnevictable(page)) {
>> del_page_from_lru_list(page, lruvec, page_lru(page));
>> ClearPageActive(page);
>> add_page_to_lru_list_tail(page, lruvec, page_lru(page));
>> @@ -306,7 +312,7 @@ void lru_note_cost_page(struct page *page)
>>
>> static void __activate_page(struct page *page, struct lruvec *lruvec)
>> {
>> - if (PageLRU(page) && !PageActive(page) && !PageUnevictable(page)) {
>> + if (!PageActive(page) && !PageUnevictable(page)) {
>> int lru = page_lru_base_type(page);
>> int nr_pages = thp_nr_pages(page);
>>
>> @@ -362,7 +368,8 @@ void activate_page(struct page *page)
>>
>> page = compound_head(page);
>> spin_lock_irq(&pgdat->lru_lock);
>> - __activate_page(page, mem_cgroup_page_lruvec(page, pgdat));
>> + if (PageLRU(page))
>> + __activate_page(page, mem_cgroup_page_lruvec(page, pgdat));
>> spin_unlock_irq(&pgdat->lru_lock);
>> }
>> #endif
>
> Every time I look at this, I wonder if that's right, or an unnecessary
> optimization strayed in, or whatever. For the benefit of others looking
> at this patch, yes it is right: this is the !CONFIG_SMP alternative
> version of activate_page(), and needs that PageLRU check to compensate
> for the check that has now been removed from __activate_page() itself.
>
>> @@ -521,9 +528,6 @@ static void lru_deactivate_file_fn(struct page *page, struct lruvec *lruvec)
>> bool active;
>> int nr_pages = thp_nr_pages(page);
>>
>> - if (!PageLRU(page))
>> - return;
>> -
>> if (PageUnevictable(page))
>> return;
>>
>> @@ -564,7 +568,7 @@ static void lru_deactivate_file_fn(struct page *page, struct lruvec *lruvec)
>>
>> static void lru_deactivate_fn(struct page *page, struct lruvec *lruvec)
>> {
>> - if (PageLRU(page) && PageActive(page) && !PageUnevictable(page)) {
>> + if (PageActive(page) && !PageUnevictable(page)) {
>> int lru = page_lru_base_type(page);
>> int nr_pages = thp_nr_pages(page);
>>
>> @@ -581,7 +585,7 @@ static void lru_deactivate_fn(struct page *page, struct lruvec *lruvec)
>>
>> static void lru_lazyfree_fn(struct page *page, struct lruvec *lruvec)
>> {
>> - if (PageLRU(page) && PageAnon(page) && PageSwapBacked(page) &&
>> + if (PageAnon(page) && PageSwapBacked(page) &&
>> !PageSwapCache(page) && !PageUnevictable(page)) {
>> bool active = PageActive(page);
>> int nr_pages = thp_nr_pages(page);
>> @@ -979,7 +983,29 @@ static void __pagevec_lru_add_fn(struct page *page, struct lruvec *lruvec)
>> */
>> void __pagevec_lru_add(struct pagevec *pvec)
>> {
>> - pagevec_lru_move_fn(pvec, __pagevec_lru_add_fn);
>> + int i;
>> + struct pglist_data *pgdat = NULL;
>> + struct lruvec *lruvec;
>> + unsigned long flags = 0;
>> +
>> + for (i = 0; i < pagevec_count(pvec); i++) {
>> + struct page *page = pvec->pages[i];
>> + struct pglist_data *pagepgdat = page_pgdat(page);
>> +
>> + if (pagepgdat != pgdat) {
>> + if (pgdat)
>> + spin_unlock_irqrestore(&pgdat->lru_lock, flags);
>> + pgdat = pagepgdat;
>> + spin_lock_irqsave(&pgdat->lru_lock, flags);
>> + }
>> +
>> + lruvec = mem_cgroup_page_lruvec(page, pgdat);
>> + __pagevec_lru_add_fn(page, lruvec);
>> + }
>> + if (pgdat)
>> + spin_unlock_irqrestore(&pgdat->lru_lock, flags);
>> + release_pages(pvec->pages, pvec->nr);
>> + pagevec_reinit(pvec);
>> }
>>
>> /**
>> --
>> 1.8.3.1