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    Subject[PATCH -mm 5/5] memcg: use spinlock in page_cgroup instead of bit_spinlock
    From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>

    This patch replaces bit_spinlock with spinlock. In general,
    spinlock has good functinality than bit_spin_lock and we should use
    it if we have a room for it. In 64bit arch, we have extra 4bytes.
    Let's use it.
    expected effects:
    - use better codes.
    - ticket lock on x86-64
    - para-vitualization aware lock
    etc..

    Chagelog: 20090729
    - fixed page_cgroup_is_locked().

    Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
    --
    ---
    include/linux/page_cgroup.h | 33 ++++++++++++++++++++++++++++++++-
    mm/memcontrol.c | 2 +-
    mm/page_cgroup.c | 3 +++
    3 files changed, 36 insertions(+), 2 deletions(-)

    Index: mmotm-0727/include/linux/page_cgroup.h
    ===================================================================
    --- mmotm-0727.orig/include/linux/page_cgroup.h
    +++ mmotm-0727/include/linux/page_cgroup.h
    @@ -10,8 +10,14 @@
    * All page cgroups are allocated at boot or memory hotplug event,
    * then the page cgroup for pfn always exists.
    */
    +#ifdef CONFIG_64BIT
    +#define PCG_HAS_SPINLOCK
    +#endif
    struct page_cgroup {
    unsigned long flags;
    +#ifdef PCG_HAS_SPINLOCK
    + spinlock_t lock;
    +#endif
    unsigned short mem_cgroup; /* ID of assigned memory cgroup */
    unsigned short blk_cgroup; /* Not Used..but will be. */
    struct page *page;
    @@ -36,7 +42,9 @@ struct page_cgroup *lookup_page_cgroup(s

    enum {
    /* flags for mem_cgroup */
    - PCG_LOCK, /* page cgroup is locked */
    +#ifndef PCG_HAS_SPINLOCK
    + PCG_LOCK, /* page cgroup is locked (see below also.)*/
    +#endif
    PCG_CACHE, /* charged as cache */
    PCG_USED, /* this object is in use. */
    PCG_ACCT_LRU, /* page has been accounted for */
    @@ -65,8 +73,6 @@ static inline void ClearPageCgroup##unam
    static inline int TestClearPageCgroup##uname(struct page_cgroup *pc) \
    { return test_and_clear_bit(PCG_##lname, &pc->flags); }

    -TESTPCGFLAG(Locked, LOCK)
    -
    /* Cache flag is set only once (at allocation) */
    TESTPCGFLAG(Cache, CACHE)
    CLEARPCGFLAG(Cache, CACHE)
    @@ -95,6 +101,22 @@ static inline enum zone_type page_cgroup
    return page_zonenum(pc->page);
    }

    +#ifdef PCG_HAS_SPINLOCK
    +static inline void lock_page_cgroup(struct page_cgroup *pc)
    +{
    + spin_lock(&pc->lock);
    +}
    +static inline void unlock_page_cgroup(struct page_cgroup *pc)
    +{
    + spin_unlock(&pc->lock);
    +}
    +
    +static inline bool page_cgroup_is_locked(struct page_cgroup *pc)
    +{
    + return spin_is_locked(&pc->lock);
    +}
    +
    +#else
    static inline void lock_page_cgroup(struct page_cgroup *pc)
    {
    bit_spin_lock(PCG_LOCK, &pc->flags);
    @@ -105,6 +127,14 @@ static inline void unlock_page_cgroup(st
    bit_spin_unlock(PCG_LOCK, &pc->flags);
    }

    +static inline void page_cgroup_is_locked(struct page_cgrou *pc)
    +{
    + bit_spin_is_locked(PCG_LOCK, &pc->flags);
    +}
    +TESTPCGFLAG(Locked, LOCK)
    +
    +#endif
    +
    #else /* CONFIG_CGROUP_MEM_RES_CTLR */
    struct page_cgroup;

    Index: mmotm-0727/mm/page_cgroup.c
    ===================================================================
    --- mmotm-0727.orig/mm/page_cgroup.c
    +++ mmotm-0727/mm/page_cgroup.c
    @@ -18,6 +18,9 @@ __init_page_cgroup(struct page_cgroup *p
    pc->mem_cgroup = 0;
    pc->page = pfn_to_page(pfn);
    INIT_LIST_HEAD(&pc->lru);
    +#ifdef PCG_HAS_SPINLOCK
    + spin_lock_init(&pc->lock);
    +#endif
    }
    static unsigned long total_usage;

    Index: mmotm-0727/mm/memcontrol.c
    ===================================================================
    --- mmotm-0727.orig/mm/memcontrol.c
    +++ mmotm-0727/mm/memcontrol.c
    @@ -1999,7 +1999,7 @@ static void __mem_cgroup_move_account(st
    int i;
    VM_BUG_ON(from == to);
    VM_BUG_ON(PageLRU(pc->page));
    - VM_BUG_ON(!PageCgroupLocked(pc));
    + VM_BUG_ON(!page_cgroup_is_locked(pc));
    VM_BUG_ON(!PageCgroupUsed(pc));
    VM_BUG_ON(id_to_memcg(pc->mem_cgroup) != from);



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