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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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