Re: [PATCH 4/4] mm/page_alloc : relieve zone->lock's pressure for memory free

[Minchan Kim <minchan.kim@gmail.com>]

On Mon, 11 Jan 2010 12:37:14 +0800
Huang Shijie <shijie8@gmail.com> wrote:

>   Move the __mod_zone_page_state out the guard region of
> the spinlock to relieve the pressure for memory free.
> 
> Signed-off-by: Huang Shijie <shijie8@gmail.com>
> ---
>  mm/page_alloc.c |   26 ++++++++++++++++----------
>  1 files changed, 16 insertions(+), 10 deletions(-)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 290dfc3..34b9a3a 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -530,12 +530,9 @@ static void free_pcppages_bulk(struct zone *zone, int count,
>  {
>  	int migratetype = 0;
>  	int batch_free = 0;
> +	int free_ok = 0;
>  
>  	spin_lock(&zone->lock);
> -	zone_clear_flag(zone, ZONE_ALL_UNRECLAIMABLE);
> -	zone->pages_scanned = 0;


We don't use zone->lock to protect pages_scanned in shrink_[in]active_list.
At least, we can move zone->pages_scanned out of lock.

In addition, 
sometime we don't use lock to test ZONE_ALL_UNRECLAIMABLE,
sometime we do use zone->lock(ex, zoneinfo_show_print). 

Now lock for ZONE_ALL_UNRECLAIMABLE is not consistent, 

I think we have to use not zone->lock but zone->lru_lock 
since it's related to reclaim. 

Few days ago, Mel and Kosaki discussed about zone->lock. 
Any thought?

> -
> -	__mod_zone_page_state(zone, NR_FREE_PAGES, count);
>  	while (count) {
>  		struct page *page;
>  		struct list_head *list;
> @@ -558,23 +555,32 @@ static void free_pcppages_bulk(struct zone *zone, int count,
>  			page = list_entry(list->prev, struct page, lru);
>  			/* must delete as __free_one_page list manipulates */
>  			list_del(&page->lru);
> -			__free_one_page(page, zone, 0, migratetype);
> +			free_ok += __free_one_page(page, zone, 0, migratetype);
>  			trace_mm_page_pcpu_drain(page, 0, migratetype);
>  		} while (--count && --batch_free && !list_empty(list));
>  	}
> +
> +	if (likely(free_ok)) {
> +		zone_clear_flag(zone, ZONE_ALL_UNRECLAIMABLE);
> +		zone->pages_scanned = 0;
> +	}
>  	spin_unlock(&zone->lock);
> +	__mod_zone_page_state(zone, NR_FREE_PAGES, free_ok);
>  }
>  
>  static void free_one_page(struct zone *zone, struct page *page, int order,
>  				int migratetype)
>  {
> -	spin_lock(&zone->lock);
> -	zone_clear_flag(zone, ZONE_ALL_UNRECLAIMABLE);
> -	zone->pages_scanned = 0;
> +	int free_ok;
>  
> -	__mod_zone_page_state(zone, NR_FREE_PAGES, 1 << order);
> -	__free_one_page(page, zone, order, migratetype);
> +	spin_lock(&zone->lock);
> +	free_ok = __free_one_page(page, zone, order, migratetype);
> +	if (likely(free_ok)) {
> +		zone_clear_flag(zone, ZONE_ALL_UNRECLAIMABLE);
> +		zone->pages_scanned = 0;
> +	}
>  	spin_unlock(&zone->lock);
> +	__mod_zone_page_state(zone, NR_FREE_PAGES, free_ok << order);
>  }
>  
>  static void __free_pages_ok(struct page *page, unsigned int order)
> -- 
> 1.6.5.2
> 
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-- 
Kind regards,
Minchan Kim

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