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SubjectRe: [PATCH v3 20/21] mm: split zone->lru_lock
On Thu, 23 Feb 2012 17:53:23 +0400
Konstantin Khlebnikov <khlebnikov@openvz.org> 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@openvz.org>

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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