Re: [PATCH 03/13] mm: move __ClearPageLRU() into page_off_lru()

From: Michal Hocko <mhocko@suse.com>
To: Yu Zhao <yuzhao@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	Alex Shi <alex.shi@linux.alibaba.com>,
	Steven Rostedt <rostedt@goodmis.org>,
	Ingo Molnar <mingo@redhat.com>,
	Johannes Weiner <hannes@cmpxchg.org>,
	Vladimir Davydov <vdavydov.dev@gmail.com>,
	Roman Gushchin <guro@fb.com>, Shakeel Butt <shakeelb@google.com>,
	Chris Down <chris@chrisdown.name>,
	Yafang Shao <laoar.shao@gmail.com>,
	Vlastimil Babka <vbabka@suse.cz>,
	Huang Ying <ying.huang@intel.com>,
	Pankaj Gupta <pankaj.gupta.linux@gmail.com>,
	Matthew Wilcox <willy@infradead.org>,
	Konstantin Khlebnikov <koct9i@gmail.com>,
	Minchan Kim <minchan@kernel.org>,
	Jaewon Kim <jaewon31.kim@samsung.com>,
	cgroups@vger.kernel.org, linux-mm@kvack.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH 03/13] mm: move __ClearPageLRU() into page_off_lru()
Date: Fri, 18 Sep 2020 09:38:07 +0200	[thread overview]
Message-ID: <20200918073807.GF28827@dhcp22.suse.cz> (raw)
In-Reply-To: <20200918030051.650890-4-yuzhao@google.com>

On Thu 17-09-20 21:00:41, Yu Zhao wrote:
> Now we have a total of three places that free lru pages when their
> references become zero (after we drop the reference from isolation).
> 
> Before this patch, they all do:
> 	__ClearPageLRU()
> 	page_off_lru()
> 	del_page_from_lru_list()
> 
> After this patch, they become:
> 	page_off_lru()
> 		__ClearPageLRU()
> 	del_page_from_lru_list()
> 
> This change should have no side effects.

Again, why this is desirable?

> Signed-off-by: Yu Zhao <yuzhao@google.com>
> ---
>  include/linux/mm_inline.h | 1 +
>  mm/swap.c                 | 2 --
>  mm/vmscan.c               | 1 -
>  3 files changed, 1 insertion(+), 3 deletions(-)
> 
> diff --git a/include/linux/mm_inline.h b/include/linux/mm_inline.h
> index 8fc71e9d7bb0..be9418425e41 100644
> --- a/include/linux/mm_inline.h
> +++ b/include/linux/mm_inline.h
> @@ -92,6 +92,7 @@ static __always_inline enum lru_list page_off_lru(struct page *page)
>  {
>  	enum lru_list lru;
>  
> +	__ClearPageLRU(page);
>  	if (PageUnevictable(page)) {
>  		__ClearPageUnevictable(page);
>  		lru = LRU_UNEVICTABLE;
> diff --git a/mm/swap.c b/mm/swap.c
> index 40bf20a75278..8362083f00c9 100644
> --- a/mm/swap.c
> +++ b/mm/swap.c
> @@ -86,7 +86,6 @@ static void __page_cache_release(struct page *page)
>  		spin_lock_irqsave(&pgdat->lru_lock, flags);
>  		lruvec = mem_cgroup_page_lruvec(page, pgdat);
>  		VM_BUG_ON_PAGE(!PageLRU(page), page);
> -		__ClearPageLRU(page);
>  		del_page_from_lru_list(page, lruvec, page_off_lru(page));
>  		spin_unlock_irqrestore(&pgdat->lru_lock, flags);
>  	}
> @@ -895,7 +894,6 @@ void release_pages(struct page **pages, int nr)
>  
>  			lruvec = mem_cgroup_page_lruvec(page, locked_pgdat);
>  			VM_BUG_ON_PAGE(!PageLRU(page), page);
> -			__ClearPageLRU(page);
>  			del_page_from_lru_list(page, lruvec, page_off_lru(page));
>  		}
>  
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index f257d2f61574..f9a186a96410 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -1862,7 +1862,6 @@ static unsigned noinline_for_stack move_pages_to_lru(struct lruvec *lruvec,
>  		add_page_to_lru_list(page, lruvec, lru);
>  
>  		if (put_page_testzero(page)) {
> -			__ClearPageLRU(page);
>  			del_page_from_lru_list(page, lruvec, page_off_lru(page));
>  
>  			if (unlikely(PageCompound(page))) {
> -- 
> 2.28.0.681.g6f77f65b4e-goog

-- 
Michal Hocko
SUSE Labs