Re: [PATCH 9/9] mm/swap: count a new anonymous page as a reclaim_state's rotate

[Hillf Danton <hdanton@sina.com>]

On Mon, 10 Feb 2020 22:20:37 -0800 (PST)
> From: Joonsoo Kim <iamjoonsoo.kim@lge.com>
> 
> reclaim_stat's rotate is used for controlling the ratio of scanning page
> between file and anonymous LRU. All new anonymous pages are counted
> for rotate before the patch, protecting anonymous pages on active LRU, and,
> it makes that reclaim on anonymous LRU is less happened than file LRU.
> 
> Now, situation is changed. all new anonymous pages are not added
> to the active LRU so rotate would be far less than before. It will cause
> that reclaim on anonymous LRU happens more and it would result in bad
> effect on some system that is optimized for previous setting.
> 
> Therefore, this patch counts a new anonymous page as a reclaim_state's
> rotate. Although it is non-logical to add this count to
> the reclaim_state's rotate in current algorithm, reducing the regression
> would be more important.
> 
> I found this regression on kernel-build test and it is roughly 2~5%
> performance degradation. With this workaround, performance is completely
> restored.
> 
> Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
> ---
>  mm/swap.c | 27 ++++++++++++++++++++++++++-
>  1 file changed, 26 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/swap.c b/mm/swap.c
> index 18b2735..c3584af 100644
> --- a/mm/swap.c
> +++ b/mm/swap.c
> @@ -187,6 +187,9 @@ int get_kernel_page(unsigned long start, int write, struct page **pages)
>  }
>  EXPORT_SYMBOL_GPL(get_kernel_page);
>  
> +static void __pagevec_lru_add_fn(struct page *page, struct lruvec *lruvec,
> +				 void *arg);
> +
>  static void pagevec_lru_move_fn(struct pagevec *pvec,
>  	void (*move_fn)(struct page *page, struct lruvec *lruvec, void *arg),
>  	void *arg)
> @@ -207,6 +210,19 @@ static void pagevec_lru_move_fn(struct pagevec *pvec,
>  			spin_lock_irqsave(&pgdat->lru_lock, flags);
>  		}
>  
> +		if (move_fn == __pagevec_lru_add_fn) {
> +			struct list_head *entry = &page->lru;
> +			unsigned long next = (unsigned long)entry->next;
> +			unsigned long rotate = next & 2;
> +
> +			if (rotate) {
> +				VM_BUG_ON(arg);
> +
> +				next = next & ~2;
> +				entry->next = (struct list_head *)next;
> +				arg = (void *)rotate;
> +			}
> +		}
>  		lruvec = mem_cgroup_page_lruvec(page, pgdat);
>  		(*move_fn)(page, lruvec, arg);
>  	}
> @@ -475,6 +491,14 @@ void lru_cache_add_inactive_or_unevictable(struct page *page,
>  				    hpage_nr_pages(page));
>  		count_vm_event(UNEVICTABLE_PGMLOCKED);
>  	}
> +
> +	if (PageSwapBacked(page) && evictable) {
> +		struct list_head *entry = &page->lru;
> +		unsigned long next = (unsigned long)entry->next;
> +
> +		next = next | 2;
> +		entry->next = (struct list_head *)next;
> +	}
>  	lru_cache_add(page);
>  }
>  
> @@ -927,6 +951,7 @@ static void __pagevec_lru_add_fn(struct page *page, struct lruvec *lruvec,
>  {
>  	enum lru_list lru;
>  	int was_unevictable = TestClearPageUnevictable(page);
> +	unsigned long rotate = (unsigned long)arg;
>  
>  	VM_BUG_ON_PAGE(PageLRU(page), page);
>  
> @@ -962,7 +987,7 @@ static void __pagevec_lru_add_fn(struct page *page, struct lruvec *lruvec,
>  	if (page_evictable(page)) {
>  		lru = page_lru(page);
>  		update_page_reclaim_stat(lruvec, page_is_file_cache(page),
> -					 PageActive(page));
> +					 PageActive(page) | rotate);


Is it likely to rotate a page if we know it's not active?

 		update_page_reclaim_stat(lruvec, page_is_file_cache(page),
-					 PageActive(page));
+					 PageActive(page) ||
+					 !page_is_file_cache(page));


>  		if (was_unevictable)
>  			count_vm_event(UNEVICTABLE_PGRESCUED);
>  	} else {
> -- 
> 2.7.4