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    SubjectRe: [PATCH v3 14/21] mm: introduce lruvec locking primitives
    On Thu, 23 Feb 2012 17:52:47 +0400
    Konstantin Khlebnikov <khlebnikov@openvz.org> wrote:

    > This is initial preparation for lru_lock splitting.
    >
    > This locking primites designed to hide splitted nature of lru_lock
    > and to avoid overhead for non-splitted lru_lock in non-memcg case.
    >
    > * Lock via lruvec reference
    >
    > lock_lruvec(lruvec, flags)
    > lock_lruvec_irq(lruvec)
    >
    > * Lock via page reference
    >
    > lock_page_lruvec(page, flags)
    > lock_page_lruvec_irq(page)
    > relock_page_lruvec(lruvec, page, flags)
    > relock_page_lruvec_irq(lruvec, page)
    > __relock_page_lruvec(lruvec, page) ( lruvec != NULL, page in same zone )
    >
    > They always returns pointer to some locked lruvec, page anyway can be
    > not in lru, PageLRU() sign is stable while we hold returned lruvec lock.
    > Caller must guarantee page to lruvec reference validity.
    >
    > * Lock via page, without stable page reference
    >
    > __lock_page_lruvec_irq(&lruvec, page)
    >
    > It returns true of lruvec succesfully locked and PageLRU is set.
    > Initial lruvec can be NULL. Consequent calls must be in the same zone.
    >
    > * Unlock
    >
    > unlock_lruvec(lruvec, flags)
    > unlock_lruvec_irq(lruvec)
    >
    > * Wait
    >
    > wait_lruvec_unlock(lruvec)
    > Wait for lruvec unlock, caller must have stable reference to lruvec.
    >
    > __wait_lruvec_unlock(lruvec)
    > Wait for lruvec unlock before locking other lrulock for same page,
    > nothing if there only one possible lruvec per page.
    > Used at page-to-lruvec reference switching to stabilize PageLRU sign.
    >
    > Signed-off-by: Konstantin Khlebnikov <khlebnikov@openvz.org>

    O.K. I like this.

    Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>

    Hmm....Could you add a comment in memcg part ? (see below)



    > ---
    > mm/huge_memory.c | 8 +-
    > mm/internal.h | 176 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
    > mm/memcontrol.c | 14 ++--
    > mm/swap.c | 58 ++++++------------
    > mm/vmscan.c | 77 ++++++++++--------------
    > 5 files changed, 237 insertions(+), 96 deletions(-)
    >
    > diff --git a/mm/huge_memory.c b/mm/huge_memory.c
    > index 09e7069..74996b8 100644
    > --- a/mm/huge_memory.c
    > +++ b/mm/huge_memory.c
    > @@ -1228,13 +1228,11 @@ static int __split_huge_page_splitting(struct page *page,
    > static void __split_huge_page_refcount(struct page *page)
    > {
    > int i;
    > - struct zone *zone = page_zone(page);
    > struct lruvec *lruvec;
    > int tail_count = 0;
    >
    > /* prevent PageLRU to go away from under us, and freeze lru stats */
    > - spin_lock_irq(&zone->lru_lock);
    > - lruvec = page_lruvec(page);
    > + lruvec = lock_page_lruvec_irq(page);
    > compound_lock(page);
    > /* complete memcg works before add pages to LRU */
    > mem_cgroup_split_huge_fixup(page);
    > @@ -1316,11 +1314,11 @@ static void __split_huge_page_refcount(struct page *page)
    > BUG_ON(atomic_read(&page->_count) <= 0);
    >
    > __dec_zone_page_state(page, NR_ANON_TRANSPARENT_HUGEPAGES);
    > - __mod_zone_page_state(zone, NR_ANON_PAGES, HPAGE_PMD_NR);
    > + __mod_zone_page_state(lruvec_zone(lruvec), NR_ANON_PAGES, HPAGE_PMD_NR);
    >
    > ClearPageCompound(page);
    > compound_unlock(page);
    > - spin_unlock_irq(&zone->lru_lock);
    > + unlock_lruvec_irq(lruvec);
    >
    > for (i = 1; i < HPAGE_PMD_NR; i++) {
    > struct page *page_tail = page + i;
    > diff --git a/mm/internal.h b/mm/internal.h
    > index ef49dbf..9454752 100644
    > --- a/mm/internal.h
    > +++ b/mm/internal.h
    > @@ -13,6 +13,182 @@
    >
    > #include <linux/mm.h>
    >
    > +static inline void lock_lruvec(struct lruvec *lruvec, unsigned long *flags)
    > +{
    > + spin_lock_irqsave(&lruvec_zone(lruvec)->lru_lock, *flags);
    > +}
    > +
    > +static inline void lock_lruvec_irq(struct lruvec *lruvec)
    > +{
    > + spin_lock_irq(&lruvec_zone(lruvec)->lru_lock);
    > +}
    > +
    > +static inline void unlock_lruvec(struct lruvec *lruvec, unsigned long *flags)
    > +{
    > + spin_unlock_irqrestore(&lruvec_zone(lruvec)->lru_lock, *flags);
    > +}
    > +
    > +static inline void unlock_lruvec_irq(struct lruvec *lruvec)
    > +{
    > + spin_unlock_irq(&lruvec_zone(lruvec)->lru_lock);
    > +}
    > +
    > +static inline void wait_lruvec_unlock(struct lruvec *lruvec)
    > +{
    > + spin_unlock_wait(&lruvec_zone(lruvec)->lru_lock);
    > +}
    > +
    > +#ifdef CONFIG_CGROUP_MEM_RES_CTLR
    > +
    > +/* Dynamic page to lruvec mapping */
    > +
    > +/* Lock other lruvec for other page in the same zone */
    > +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);
    > +}
    > +
    > +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);
    > + }
    > + return page_lruvec(page);
    > +}

    Could you add comments/caution to the caller

    - !PageLRU(page) case ?
    - Can the caller assume page_lruvec(page) == lruvec ? If no, which lru_vec is locked ?

    etc...

    > +
    > +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);
    > + }
    > + return page_lruvec(page);
    > +}


    Same here.

    Thanks,
    -Kame



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