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From: Greg Thelen on 28 Jul 2010 02:20
KAMEZAWA Hiroyuki <kamezawa.hiroyu(a)jp.fujitsu.com> writes:

> From: KAMEZAWA Hiroyuki <kamezawa.hiroyu(a)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(a)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

> +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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Prev: linux-next: build failure after merge of the final tree (scsi tree related)
Next: [BUGFIX] trace, fix ring_buffer_read_page reading out of page boundary