Re: [PATCH 2/4] memcg: fix USED bit handling at uncharge in THP

[Johannes Weiner]

Hello KAMEZAWA-san,

On Tue, Jan 18, 2011 at 11:40:49AM +0900, KAMEZAWA Hiroyuki wrote:
> +void mem_cgroup_split_huge_fixup(struct page *head, struct page *tail)
> +{
> +	struct page_cgroup *head_pc = lookup_page_cgroup(head);
> +	struct page_cgroup *tail_pc = lookup_page_cgroup(tail);
> +	unsigned long flags;
> +
> +	/*
> +	 * We have no races witch charge/uncharge but will have races with
> +	 * page state accounting.
> +	 */
> +	move_lock_page_cgroup(head_pc, &flags);
> +
> +	tail_pc->mem_cgroup = head_pc->mem_cgroup;
> +	smp_wmb(); /* see __commit_charge() */

I thought the barriers were needed because charging does not hold the
lru lock.  But here we do, and all the 'lockless' read-sides do so as
well.  Am I missing something or can this barrier be removed?

	Hannes
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/