Re: [PATCH 1/2] mm: use add_page_to_lru_list()/page_lru()/page_off_lru()

[Yu Zhao]

On Sun, Aug 30, 2020 at 05:44:04PM -0600, Yu Zhao wrote:
> On Sun, Aug 30, 2020 at 04:31:38PM +0800, Alex Shi wrote:
> > 
> > 
> > 在 2020/8/30 上午2:12, Yu Zhao 写道:
> > > On Thu, Aug 27, 2020 at 05:42:01PM -0600, Yu Zhao wrote:
> > >> This is a trivial but worth having clean-up patch. There should be
> > >> no side effects except page->lru is temporarily poisoned after it's
> > >> deleted but before it's added to the new list in move_pages_to_lru()
> > >> (which is not a problem).
> > >>
> > >> Signed-off-by: Yu Zhao <yuzhao@xxxxxxxxxx>
> > > 
> > > Hi Alex, I just realized your
> > >   [v18,08/32] mm/vmscan: remove unnecessary lruvec adding
> > > at
> > >   https://patchwork.kernel.org/patch/11733123/
> > > also touches move_pages_to_lru(). I agree it's better not to add
> > > a page we are going to free to the list in the first place. The
> > > rest in this patch would be too trivial to be a separate one (on
> > > top of yours).
> > > 
> > > So would you mind taking of the clean-up too in your series? I'll
> > > drop this one then. Thanks.
> 
> Ok, maybe I wasn't clear before. Please see what exactly I'm asking
> you to consider below.
> 
> > >> diff --git a/mm/swap.c b/mm/swap.c
> > >> index 40bf20a75278..2735ecf0f566 100644
> > >> --- a/mm/swap.c
> > >> +++ b/mm/swap.c
> > >> @@ -597,11 +597,9 @@ static void lru_lazyfree_fn(struct page *page, struct lruvec *lruvec,
> > >>  {
> > >>  	if (PageLRU(page) && PageAnon(page) && PageSwapBacked(page) &&
> > >>  	    !PageSwapCache(page) && !PageUnevictable(page)) {
> > >> -		bool active = PageActive(page);
> > >>  		int nr_pages = thp_nr_pages(page);
> > >>  
> > >> -		del_page_from_lru_list(page, lruvec,
> > >> -				       LRU_INACTIVE_ANON + active);
> > >> +		del_page_from_lru_list(page, lruvec, page_lru(page));
> > >>  		ClearPageActive(page);
> > >>  		ClearPageReferenced(page);
> > >>  		/*
> 
> 1) The above has no conflict with your series and therefore can go
> separately. Feel free to include it.
> 
> > >> diff --git a/mm/vmscan.c b/mm/vmscan.c
> > >> index 99e1796eb833..b479ced26cd3 100644
> > >> --- a/mm/vmscan.c
> > >> +++ b/mm/vmscan.c
> > >> @@ -1845,13 +1845,12 @@ static unsigned noinline_for_stack move_pages_to_lru(struct lruvec *lruvec,
> > >>  	int nr_pages, nr_moved = 0;
> > >>  	LIST_HEAD(pages_to_free);
> > >>  	struct page *page;
> > >> -	enum lru_list lru;
> > >>  
> > >>  	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);
> 
> 2) The above is the same change you've made.
> 
> > >> @@ -1860,16 +1859,10 @@ static unsigned noinline_for_stack move_pages_to_lru(struct lruvec *lruvec,
> > >>  		lruvec = mem_cgroup_page_lruvec(page, pgdat);
> > >>  
> > >>  		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]);
> > >> +		add_page_to_lru_list(page, lruvec, page_lru(page));
> > >>  
> > >>  		if (put_page_testzero(page)) {
> > >> -			__ClearPageLRU(page);
> > 
> > it's interesting to know the PageLRU left has no bad impact in real life. 
> > it justs seems a path confliction with my that patch. 
> 
> (No, we can't leave PG_lru uncleared. It's done by the page_off_lru()
> right below).

Sorry about this false claim. You are right: we need to keep
__ClearPageLRU() here. page_off_lru() doesn't do it for us.

I'll fix this in v2. Thanks.