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SubjectRe: [PATCH v3 14/21] mm: introduce lruvec locking primitives
KAMEZAWA Hiroyuki wrote:
> 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 ?

Yes, caller can assume page_lruvec(page) == lruvec. And PageLRU() is stable,
it means it stays true or false while this lruvec 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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