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    SubjectRe: [RFC][PATCH 7/7][memcg] use spin lock instead of bit_spin_lock in page_cgroup
    On Tue, 27 Jul 2010 23:16:54 -0700
    Greg Thelen <gthelen@google.com> wrote:

    > KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> writes:
    >
    > > From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
    > >
    > > This patch replaces page_cgroup's bit_spinlock with spinlock. In general,
    > > spinlock has good implementation 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.
    > >
    > > Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
    > > --
    > > Index: mmotm-0719/include/linux/page_cgroup.h
    > > ===================================================================
    > > --- mmotm-0719.orig/include/linux/page_cgroup.h
    > > +++ mmotm-0719/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;
    > > @@ -90,6 +96,16 @@ 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);
    > > +}
    >
    > This is minor issue, but this patch breaks usage of PageCgroupLocked().
    > Example from __mem_cgroup_move_account() cases panic:
    > VM_BUG_ON(!PageCgroupLocked(pc));
    >
    > I assume that this patch should also delete the following:
    > - PCG_LOCK definition from page_cgroup.h
    > - TESTPCGFLAG(Locked, LOCK) from page_cgroup.h
    > - PCGF_LOCK from memcontrol.c
    >

    yes. thank you.

    -Kame



    > > +static inline void unlock_page_cgroup(struct page_cgroup *pc)
    > > +{
    > > + spin_unlock(&pc->lock);
    > > +}
    > > +#else
    > > static inline void lock_page_cgroup(struct page_cgroup *pc)
    > > {
    > > bit_spin_lock(PCG_LOCK, &pc->flags);
    > > @@ -99,6 +115,7 @@ static inline void unlock_page_cgroup(st
    > > {
    > > bit_spin_unlock(PCG_LOCK, &pc->flags);
    > > }
    > > +#endif
    > >
    > > static inline void SetPCGFileFlag(struct page_cgroup *pc, int idx)
    > > {
    > > Index: mmotm-0719/mm/page_cgroup.c
    > > ===================================================================
    > > --- mmotm-0719.orig/mm/page_cgroup.c
    > > +++ mmotm-0719/mm/page_cgroup.c
    > > @@ -17,6 +17,9 @@ __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;
    > >
    >
    > --
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    >



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