Re: [PATCH 05/10] mm: remove LRU balancing effect of temporary page isolation

[Minchan Kim <minchan@kernel.org>]

On Mon, Jun 06, 2016 at 03:48:31PM -0400, Johannes Weiner wrote:
> Isolating an existing LRU page and subsequently putting it back on the
> list currently influences the balance between the anon and file LRUs.
> For example, heavy page migration or compaction could influence the
> balance between the LRUs and make one type more attractive when that
> type of page is affected more than the other. That doesn't make sense.
> 
> Add a dedicated LRU cache for putback, so that we can tell new LRU
> pages from existing ones at the time of linking them to the lists.
> 
> Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
> ---
>  include/linux/pagevec.h |  2 +-
>  include/linux/swap.h    |  1 +
>  mm/mlock.c              |  2 +-
>  mm/swap.c               | 34 ++++++++++++++++++++++++++++------
>  mm/vmscan.c             |  2 +-
>  5 files changed, 32 insertions(+), 9 deletions(-)
> 
> diff --git a/include/linux/pagevec.h b/include/linux/pagevec.h
> index b45d391b4540..3f8a2a01131c 100644
> --- a/include/linux/pagevec.h
> +++ b/include/linux/pagevec.h
> @@ -21,7 +21,7 @@ struct pagevec {
>  };
>  
>  void __pagevec_release(struct pagevec *pvec);
> -void __pagevec_lru_add(struct pagevec *pvec);
> +void __pagevec_lru_add(struct pagevec *pvec, bool new);
>  unsigned pagevec_lookup_entries(struct pagevec *pvec,
>  				struct address_space *mapping,
>  				pgoff_t start, unsigned nr_entries,
> diff --git a/include/linux/swap.h b/include/linux/swap.h
> index 38fe1e91ba55..178f084365c2 100644
> --- a/include/linux/swap.h
> +++ b/include/linux/swap.h
> @@ -296,6 +296,7 @@ extern unsigned long nr_free_pagecache_pages(void);
>  
>  /* linux/mm/swap.c */
>  extern void lru_cache_add(struct page *);
> +extern void lru_cache_putback(struct page *page);
>  extern void lru_add_page_tail(struct page *page, struct page *page_tail,
>  			 struct lruvec *lruvec, struct list_head *head);
>  extern void activate_page(struct page *);
> diff --git a/mm/mlock.c b/mm/mlock.c
> index 96f001041928..449c291a286d 100644
> --- a/mm/mlock.c
> +++ b/mm/mlock.c
> @@ -264,7 +264,7 @@ static void __putback_lru_fast(struct pagevec *pvec, int pgrescued)
>  	 *__pagevec_lru_add() calls release_pages() so we don't call
>  	 * put_page() explicitly
>  	 */
> -	__pagevec_lru_add(pvec);
> +	__pagevec_lru_add(pvec, false);
>  	count_vm_events(UNEVICTABLE_PGRESCUED, pgrescued);
>  }
>  
> diff --git a/mm/swap.c b/mm/swap.c
> index c6936507abb5..576c721f210b 100644
> --- a/mm/swap.c
> +++ b/mm/swap.c
> @@ -44,6 +44,7 @@
>  int page_cluster;
>  
>  static DEFINE_PER_CPU(struct pagevec, lru_add_pvec);
> +static DEFINE_PER_CPU(struct pagevec, lru_putback_pvec);
>  static DEFINE_PER_CPU(struct pagevec, lru_rotate_pvecs);
>  static DEFINE_PER_CPU(struct pagevec, lru_deactivate_file_pvecs);
>  static DEFINE_PER_CPU(struct pagevec, lru_deactivate_pvecs);
> @@ -405,12 +406,23 @@ void lru_cache_add(struct page *page)
>  
>  	get_page(page);
>  	if (!pagevec_space(pvec))
> -		__pagevec_lru_add(pvec);
> +		__pagevec_lru_add(pvec, true);
>  	pagevec_add(pvec, page);
>  	put_cpu_var(lru_add_pvec);
>  }
>  EXPORT_SYMBOL(lru_cache_add);
>  
> +void lru_cache_putback(struct page *page)
> +{
> +	struct pagevec *pvec = &get_cpu_var(lru_putback_pvec);
> +
> +	get_page(page);
> +	if (!pagevec_space(pvec))
> +		__pagevec_lru_add(pvec, false);
> +	pagevec_add(pvec, page);
> +	put_cpu_var(lru_putback_pvec);
> +}
> +
>  /**
>   * add_page_to_unevictable_list - add a page to the unevictable list
>   * @page:  the page to be added to the unevictable list
> @@ -561,10 +573,15 @@ static void lru_deactivate_fn(struct page *page, struct lruvec *lruvec,
>   */
>  void lru_add_drain_cpu(int cpu)
>  {
> -	struct pagevec *pvec = &per_cpu(lru_add_pvec, cpu);
> +	struct pagevec *pvec;
> +
> +	pvec = &per_cpu(lru_add_pvec, cpu);
> +	if (pagevec_count(pvec))
> +		__pagevec_lru_add(pvec, true);
>  
> +	pvec = &per_cpu(lru_putback_pvec, cpu);
>  	if (pagevec_count(pvec))
> -		__pagevec_lru_add(pvec);
> +		__pagevec_lru_add(pvec, false);
>  
>  	pvec = &per_cpu(lru_rotate_pvecs, cpu);
>  	if (pagevec_count(pvec)) {
> @@ -819,12 +836,17 @@ static void __pagevec_lru_add_fn(struct page *page, struct lruvec *lruvec,
>  	int file = page_is_file_cache(page);
>  	int active = PageActive(page);
>  	enum lru_list lru = page_lru(page);
> +	bool new = (bool)arg;
>  
>  	VM_BUG_ON_PAGE(PageLRU(page), page);
>  
>  	SetPageLRU(page);
>  	add_page_to_lru_list(page, lruvec, lru);
> -	update_page_reclaim_stat(lruvec, file, active, hpage_nr_pages(page));
> +
> +	if (new)
> +		update_page_reclaim_stat(lruvec, file, active,
> +					 hpage_nr_pages(page));
> +
>  	trace_mm_lru_insertion(page, lru);
>  }
>  
> @@ -832,9 +854,9 @@ static void __pagevec_lru_add_fn(struct page *page, struct lruvec *lruvec,
>   * Add the passed pages to the LRU, then drop the caller's refcount
>   * on them.  Reinitialises the caller's pagevec.
>   */
> -void __pagevec_lru_add(struct pagevec *pvec)
> +void __pagevec_lru_add(struct pagevec *pvec, bool new)
>  {
> -	pagevec_lru_move_fn(pvec, __pagevec_lru_add_fn, NULL);
> +	pagevec_lru_move_fn(pvec, __pagevec_lru_add_fn, (void *)new);
>  }

Just trivial:

'new' argument would be not clear in this context what does it mean
so worth to comment it, IMO but no strong opinion.

Other than that,

Acked-by: Minchan Kim <minchan@kernel.org>