Re: [PATCH v6 2/3] memcg: move memcg reclaimable page into tail of inactive list

[Johannes Weiner <hannes@cmpxchg.org>]

On Sun, Feb 20, 2011 at 11:43:37PM +0900, Minchan Kim wrote:
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -813,6 +813,33 @@ void mem_cgroup_del_lru(struct page *page)
>  	mem_cgroup_del_lru_list(page, page_lru(page));
>  }
>  
> +/*
> + * Writeback is about to end against a page which has been marked for immediate
> + * reclaim.  If it still appears to be reclaimable, move it to the tail of the
> + * inactive list.
> + */
> +void mem_cgroup_rotate_reclaimable_page(struct page *page)
> +{
> +	struct mem_cgroup_per_zone *mz;
> +	struct page_cgroup *pc;
> +	enum lru_list lru = page_lru(page);
> +
> +	if (mem_cgroup_disabled())
> +		return;
> +
> +	pc = lookup_page_cgroup(page);
> +	/*
> +	 * Used bit is set without atomic ops but after smp_wmb().
> +	 * For making pc->mem_cgroup visible, insert smp_rmb() here.
> +	 */
> +	smp_rmb();
> +	/* unused or root page is not rotated. */
> +	if (!PageCgroupUsed(pc) || mem_cgroup_is_root(pc->mem_cgroup))
> +		return;

The placement of this barrier is confused and has been fixed up in the
meantime in other places.  It has to be between PageCgroupUsed() and
accessing pc->mem_cgroup.  You can look at the other memcg lru
functions for reference.