Re: [PATCH 6/6] [RFC][HACK] mm: Change memory management of anonymous pages on swapless systems

[Minchan Kim <minchan@kernel.org>]

Hi John,

On 06/13/2012 10:11 AM, John Stultz wrote:

> Due to my newbie-ness, the following may not be precise, but
> I think it conveys the intent of what I'm trying to do here.
> 
> Anonymous memory is tracked on two LRU lists: LRU_INACTIVE_ANON
> and LRU_ACTIVE_ANON. This split is useful when we need to free
> up pages and are trying to decide what to swap out.
> 
> However, on systems that do no have swap, this partition is less
> clear. In many cases the code avoids aging active anonymous pages
> onto the inactive list. However in some cases pages do get moved
> to the inactive list, but we never call writepage, as there isn't
> anything to swap out.


I confess I don't look at your code still yet so I might be wrong.
As I read your comment, pop old history.

Long time ago, I did prevent anon aging totally without swapless but dropped up by Rik's comment.
We should think swapoff system and swapless(!CONFIG_SWAP) separately.

Of course, in swapless system, your code would work. Even, we might not need anon lru list itself.
But in swap-off system, it is possible that user can do swapon anytime so we need keeping the aging.

That was why Rik didn't like my patch at that time.

> 
> This patch changes some of the active/inactive list management of
> anonymous memory when there is no swap. In that case pages are
> always added to the active lru. The intent is that since anonymous
> pages cannot be swapped out, they all shoudld be active.
> 
> The one exception is volatile pages, which can be moved to
> the inactive lru by calling deactivate_page().
> 
> In addition, I've changed the logic so we also do try to shrink
> the inactive anonymous lru, and call writepage. This should only
> be done if there are volatile pages on the inactive lru.
> 
> This allows us to purge volatile pages in writepage when the system
> does not have swap.
> 
> CC: Andrew Morton <akpm@linux-foundation.org>
> CC: Android Kernel Team <kernel-team@android.com>
> CC: Robert Love <rlove@google.com>
> CC: Mel Gorman <mel@csn.ul.ie>
> CC: Hugh Dickins <hughd@google.com>
> CC: Dave Hansen <dave@linux.vnet.ibm.com>
> CC: Rik van Riel <riel@redhat.com>
> CC: Dmitry Adamushko <dmitry.adamushko@gmail.com>
> CC: Dave Chinner <david@fromorbit.com>
> CC: Neil Brown <neilb@suse.de>
> CC: Andrea Righi <andrea@betterlinux.com>
> CC: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
> CC: Taras Glek <tgek@mozilla.com>
> CC: Mike Hommey <mh@glandium.org>
> CC: Jan Kara <jack@suse.cz>
> CC: KOSAKI Motohiro <kosaki.motohiro@gmail.com>
> Signed-off-by: John Stultz <john.stultz@linaro.org>
> ---
>  include/linux/pagevec.h |    5 +----
>  include/linux/swap.h    |   23 +++++++++++++++--------
>  mm/swap.c               |   13 ++++++++++++-
>  mm/vmscan.c             |    9 ---------
>  4 files changed, 28 insertions(+), 22 deletions(-)
> 
> diff --git a/include/linux/pagevec.h b/include/linux/pagevec.h
> index 2aa12b8..e1312a5 100644
> --- a/include/linux/pagevec.h
> +++ b/include/linux/pagevec.h
> @@ -22,6 +22,7 @@ struct pagevec {
>  
>  void __pagevec_release(struct pagevec *pvec);
>  void __pagevec_lru_add(struct pagevec *pvec, enum lru_list lru);
> +void __pagevec_lru_add_anon(struct pagevec *pvec);
>  unsigned pagevec_lookup(struct pagevec *pvec, struct address_space *mapping,
>  		pgoff_t start, unsigned nr_pages);
>  unsigned pagevec_lookup_tag(struct pagevec *pvec,
> @@ -64,10 +65,6 @@ static inline void pagevec_release(struct pagevec *pvec)
>  		__pagevec_release(pvec);
>  }
>  
> -static inline void __pagevec_lru_add_anon(struct pagevec *pvec)
> -{
> -	__pagevec_lru_add(pvec, LRU_INACTIVE_ANON);
> -}
>  
>  static inline void __pagevec_lru_add_active_anon(struct pagevec *pvec)
>  {
> diff --git a/include/linux/swap.h b/include/linux/swap.h
> index c84ec68..639936f 100644
> --- a/include/linux/swap.h
> +++ b/include/linux/swap.h
> @@ -238,14 +238,6 @@ extern void swap_setup(void);
>  
>  extern void add_page_to_unevictable_list(struct page *page);
>  
> -/**
> - * lru_cache_add: add a page to the page lists
> - * @page: the page to add
> - */
> -static inline void lru_cache_add_anon(struct page *page)
> -{
> -	__lru_cache_add(page, LRU_INACTIVE_ANON);
> -}
>  
>  static inline void lru_cache_add_file(struct page *page)
>  {
> @@ -474,5 +466,20 @@ mem_cgroup_uncharge_swapcache(struct page *page, swp_entry_t ent)
>  }
>  
>  #endif /* CONFIG_SWAP */
> +
> +/**
> + * lru_cache_add: add a page to the page lists
> + * @page: the page to add
> + */
> +static inline void lru_cache_add_anon(struct page *page)
> +{
> +	int lru = LRU_INACTIVE_ANON;
> +	if (!total_swap_pages)
> +		lru = LRU_ACTIVE_ANON;
> +
> +	__lru_cache_add(page, lru);
> +}
> +
> +
>  #endif /* __KERNEL__*/
>  #endif /* _LINUX_SWAP_H */
> diff --git a/mm/swap.c b/mm/swap.c
> index 4e7e2ec..f35df46 100644
> --- a/mm/swap.c
> +++ b/mm/swap.c
> @@ -691,7 +691,7 @@ void lru_add_page_tail(struct page *page, struct page *page_tail,
>  	SetPageLRU(page_tail);
>  
>  	if (page_evictable(page_tail, NULL)) {
> -		if (PageActive(page)) {
> +		if (PageActive(page) || !total_swap_pages) {
>  			SetPageActive(page_tail);
>  			active = 1;
>  			lru = LRU_ACTIVE_ANON;
> @@ -755,6 +755,17 @@ void __pagevec_lru_add(struct pagevec *pvec, enum lru_list lru)
>  }
>  EXPORT_SYMBOL(__pagevec_lru_add);
>  
> +
> +void __pagevec_lru_add_anon(struct pagevec *pvec)
> +{
> +	if (!total_swap_pages)
> +		__pagevec_lru_add(pvec, LRU_ACTIVE_ANON);
> +	else
> +		__pagevec_lru_add(pvec, LRU_INACTIVE_ANON);
> +}
> +EXPORT_SYMBOL(__pagevec_lru_add_anon);
> +
> +
>  /**
>   * pagevec_lookup - gang pagecache lookup
>   * @pvec:	Where the resulting pages are placed
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index eeb3bc9..52d8ad9 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -1597,15 +1597,6 @@ static void get_scan_count(struct lruvec *lruvec, struct scan_control *sc,
>  	if (!global_reclaim(sc))
>  		force_scan = true;
>  
> -	/* If we have no swap space, do not bother scanning anon pages. */
> -	if (!sc->may_swap || (nr_swap_pages <= 0)) {
> -		noswap = 1;
> -		fraction[0] = 0;
> -		fraction[1] = 1;
> -		denominator = 1;
> -		goto out;
> -	}
> -
>  	anon  = get_lru_size(lruvec, LRU_ACTIVE_ANON) +
>  		get_lru_size(lruvec, LRU_INACTIVE_ANON);
>  	file  = get_lru_size(lruvec, LRU_ACTIVE_FILE) +



-- 
Kind regards,
Minchan Kim