Re: [PATCH v18 19/32] mm/swap.c: serialize memcg changes in pagevec_lru_move_fn

[Alex Shi <alex.shi@linux.alibaba.com>]

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@google.com>
> 
> True.
> 
>> Signed-off-by: Hugh Dickins <hughd@google.com>
> 
> I did provide some lines, but I think it's just
> Acked-by: Hugh Dickins <hughd@google.com>
> to go below your Signed-off-by.

Thanks!
> 
>> Signed-off-by: Alex Shi <alex.shi@linux.alibaba.com>
>> Cc: Andrew Morton <akpm@linux-foundation.org>
>> Cc: linux-mm@kvack.org
>> Cc: linux-kernel@vger.kernel.org
>> ---
>>  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