Re: [PATCH v3 20/21] mm: split zone->lru_lock

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On Thu, 23 Feb 2012 17:53:23 +0400
Konstantin Khlebnikov <khlebnikov@xxxxxxxxxx> wrote:

> Looks like all ready for splitting zone->lru_lock into per-lruvec pieces.
> 
> lruvec locking loop protected with rcu, actually there is irq-disabling instead
> of rcu_read_lock(). Memory controller already releases its lru-vectors after
> syncronize_rcu() in cgroup_diput(). Probably it should be replaced with synchronize_sched()
> 
> Signed-off-by: Konstantin Khlebnikov <khlebnikov@xxxxxxxxxx>

Do we need rcu_read_lock() even if we check isolated pages at pre_destroy() ?
If pre_destroy() ends, pages under a memcg being destroyed were moved to other
cgroup while it's usolated.

So, 
 - PageLRU(page) guarantees lruvec is valid.
 - if !PageLRU(page), the caller of lru_lock should know what it does.
   Once isolated, pre_destroy() never ends and page_lruvec(page) is always stable.

Thanks,
-Kame

> ---
>  include/linux/mmzone.h |    3 +-
>  mm/compaction.c        |    2 +
>  mm/internal.h          |   66 +++++++++++++++++++++++++-----------------------
>  mm/page_alloc.c        |    2 +
>  mm/swap.c              |    2 +
>  5 files changed, 40 insertions(+), 35 deletions(-)
> 
> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
> index 2e3a298..9880150 100644
> --- a/include/linux/mmzone.h
> +++ b/include/linux/mmzone.h
> @@ -304,6 +304,8 @@ struct zone_reclaim_stat {
>  };
>  
>  struct lruvec {
> +	spinlock_t		lru_lock;
> +
>  	struct list_head	pages_lru[NR_LRU_LISTS];
>  	unsigned long		pages_count[NR_LRU_COUNTERS];
>  
> @@ -386,7 +388,6 @@ struct zone {
>  	ZONE_PADDING(_pad1_)
>  
>  	/* Fields commonly accessed by the page reclaim scanner */
> -	spinlock_t		lru_lock;
>  	struct lruvec		lruvec;
>  
>  	unsigned long		pages_scanned;	   /* since last reclaim */
> diff --git a/mm/compaction.c b/mm/compaction.c
> index fa74cbe..8661bb58 100644
> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -306,7 +306,7 @@ static isolate_migrate_t isolate_migratepages(struct zone *zone,
>  			lruvec = NULL;
>  		}
>  		if (need_resched() ||
> -		    (lruvec && spin_is_contended(&zone->lru_lock))) {
> +		    (lruvec && spin_is_contended(&lruvec->lru_lock))) {
>  			if (lruvec)
>  				unlock_lruvec_irq(lruvec);
>  			lruvec = NULL;
> diff --git a/mm/internal.h b/mm/internal.h
> index 6dd2e70..9a9fd53 100644
> --- a/mm/internal.h
> +++ b/mm/internal.h
> @@ -15,27 +15,27 @@
>  
>  static inline void lock_lruvec(struct lruvec *lruvec, unsigned long *flags)
>  {
> -	spin_lock_irqsave(&lruvec_zone(lruvec)->lru_lock, *flags);
> +	spin_lock_irqsave(&lruvec->lru_lock, *flags);
>  }
>  
>  static inline void lock_lruvec_irq(struct lruvec *lruvec)
>  {
> -	spin_lock_irq(&lruvec_zone(lruvec)->lru_lock);
> +	spin_lock_irq(&lruvec->lru_lock);
>  }
>  
>  static inline void unlock_lruvec(struct lruvec *lruvec, unsigned long *flags)
>  {
> -	spin_unlock_irqrestore(&lruvec_zone(lruvec)->lru_lock, *flags);
> +	spin_unlock_irqrestore(&lruvec->lru_lock, *flags);
>  }
>  
>  static inline void unlock_lruvec_irq(struct lruvec *lruvec)
>  {
> -	spin_unlock_irq(&lruvec_zone(lruvec)->lru_lock);
> +	spin_unlock_irq(&lruvec->lru_lock);
>  }
>  
>  static inline void wait_lruvec_unlock(struct lruvec *lruvec)
>  {
> -	spin_unlock_wait(&lruvec_zone(lruvec)->lru_lock);
> +	spin_unlock_wait(&lruvec->lru_lock);
>  }
>  
>  #ifdef CONFIG_CGROUP_MEM_RES_CTLR
> @@ -46,37 +46,39 @@ static inline void wait_lruvec_unlock(struct lruvec *lruvec)
>  static inline struct lruvec *__relock_page_lruvec(struct lruvec *locked_lruvec,
>  						  struct page *page)
>  {
> -	/* Currenyly only one lru_lock per-zone */
> -	return page_lruvec(page);
> +	struct lruvec *lruvec;
> +
> +	do {
> +		lruvec = page_lruvec(page);
> +		if (likely(lruvec == locked_lruvec))
> +			return lruvec;
> +		spin_unlock(&locked_lruvec->lru_lock);
> +		spin_lock(&lruvec->lru_lock);
> +		locked_lruvec = lruvec;
> +	} while (1);
>  }
>  
>  static inline struct lruvec *relock_page_lruvec_irq(struct lruvec *lruvec,
>  						    struct page *page)
>  {
> -	struct zone *zone = page_zone(page);
> -
>  	if (!lruvec) {
> -		spin_lock_irq(&zone->lru_lock);
> -	} else if (zone != lruvec_zone(lruvec)) {
> -		unlock_lruvec_irq(lruvec);
> -		spin_lock_irq(&zone->lru_lock);
> +		local_irq_disable();
> +		lruvec = page_lruvec(page);
> +		spin_lock(&lruvec->lru_lock);
>  	}
> -	return page_lruvec(page);
> +	return __relock_page_lruvec(lruvec, page);
>  }
>  
>  static inline struct lruvec *relock_page_lruvec(struct lruvec *lruvec,
>  						struct page *page,
>  						unsigned long *flags)
>  {
> -	struct zone *zone = page_zone(page);
> -
>  	if (!lruvec) {
> -		spin_lock_irqsave(&zone->lru_lock, *flags);
> -	} else if (zone != lruvec_zone(lruvec)) {
> -		unlock_lruvec(lruvec, flags);
> -		spin_lock_irqsave(&zone->lru_lock, *flags);
> +		local_irq_save(*flags);
> +		lruvec = page_lruvec(page);
> +		spin_lock(&lruvec->lru_lock);
>  	}
> -	return page_lruvec(page);
> +	return __relock_page_lruvec(lruvec, page);
>  }
>  
>  /*
> @@ -87,22 +89,24 @@ static inline struct lruvec *relock_page_lruvec(struct lruvec *lruvec,
>  static inline bool __lock_page_lruvec_irq(struct lruvec **lruvec,
>  					  struct page *page)
>  {
> -	struct zone *zone;
>  	bool ret = false;
>  
> +	rcu_read_lock();
> +	/*
> +	 * If we see there PageLRU(), it means page has valid lruvec link.
> +	 * We need protect whole operation with single rcu-interval, otherwise
> +	 * lruvec which hold this LRU sign can run out before we secure it.
> +	 */
>  	if (PageLRU(page)) {
>  		if (!*lruvec) {
> -			zone = page_zone(page);
> -			spin_lock_irq(&zone->lru_lock);
> -		} else
> -			zone = lruvec_zone(*lruvec);
> -
> -		if (PageLRU(page)) {
>  			*lruvec = page_lruvec(page);
> +			lock_lruvec_irq(*lruvec);
> +		}
> +		*lruvec = __relock_page_lruvec(*lruvec, page);
> +		if (PageLRU(page))
>  			ret = true;
> -		} else
> -			*lruvec = &zone->lruvec;
>  	}
> +	rcu_read_unlock();
>  
>  	return ret;
>  }
> @@ -110,7 +114,7 @@ static inline bool __lock_page_lruvec_irq(struct lruvec **lruvec,
>  /* Wait for lruvec unlock before locking other lruvec for the same page */
>  static inline void __wait_lruvec_unlock(struct lruvec *lruvec)
>  {
> -	/* Currently only one lru_lock per-zone */
> +	wait_lruvec_unlock(lruvec);
>  }
>  
>  #else /* CONFIG_CGROUP_MEM_RES_CTLR */
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index ab42446..beadcc9 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -4294,6 +4294,7 @@ void init_zone_lruvec(struct zone *zone, struct lruvec *lruvec)
>  	enum lru_list lru;
>  
>  	memset(lruvec, 0, sizeof(struct lruvec));
> +	spin_lock_init(&lruvec->lru_lock);
>  	for_each_lru(lru)
>  		INIT_LIST_HEAD(&lruvec->pages_lru[lru]);
>  #ifdef CONFIG_CGROUP_MEM_RES_CTLR
> @@ -4369,7 +4370,6 @@ static void __paginginit free_area_init_core(struct pglist_data *pgdat,
>  #endif
>  		zone->name = zone_names[j];
>  		spin_lock_init(&zone->lock);
> -		spin_lock_init(&zone->lru_lock);
>  		zone_seqlock_init(zone);
>  		zone->zone_pgdat = pgdat;
>  
> diff --git a/mm/swap.c b/mm/swap.c
> index 998c71c..8156181 100644
> --- a/mm/swap.c
> +++ b/mm/swap.c
> @@ -700,7 +700,7 @@ void lru_add_page_tail(struct lruvec *lruvec,
>  	VM_BUG_ON(!PageHead(page));
>  	VM_BUG_ON(PageCompound(page_tail));
>  	VM_BUG_ON(PageLRU(page_tail));
> -	VM_BUG_ON(NR_CPUS != 1 && !spin_is_locked(&lruvec_zone(lruvec)->lru_lock));
> +	VM_BUG_ON(NR_CPUS != 1 && !spin_is_locked(&lruvec->lru_lock));
>  
>  	SetPageLRU(page_tail);
>  
> 
> 

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