Re: [mm] [PATCH 3/4] Memory cgroup hierarchical reclaim

[KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>]

On Sun, 02 Nov 2008 00:18:49 +0530
Balbir Singh <balbir@linux.vnet.ibm.com> wrote:

> 
> This patch introduces hierarchical reclaim. When an ancestor goes over its
> limit, the charging routine points to the parent that is above its limit.
> The reclaim process then starts from the last scanned child of the ancestor
> and reclaims until the ancestor goes below its limit.
> 
> Signed-off-by: Balbir Singh <balbir@linux.vnet.ibm.com>
> ---
> 
>  mm/memcontrol.c |  153 +++++++++++++++++++++++++++++++++++++++++++++++---------
>  1 file changed, 129 insertions(+), 24 deletions(-)
> 
> diff -puN mm/memcontrol.c~memcg-hierarchical-reclaim mm/memcontrol.c
> --- linux-2.6.28-rc2/mm/memcontrol.c~memcg-hierarchical-reclaim	2008-11-02 00:14:59.000000000 +0530
> +++ linux-2.6.28-rc2-balbir/mm/memcontrol.c	2008-11-02 00:14:59.000000000 +0530
> @@ -132,6 +132,11 @@ struct mem_cgroup {
>  	 * statistics.
>  	 */
>  	struct mem_cgroup_stat stat;
> +	/*
> +	 * While reclaiming in a hiearchy, we cache the last child we
> +	 * reclaimed from.
> +	 */
> +	struct mem_cgroup *last_scanned_child;
>  };
>  static struct mem_cgroup init_mem_cgroup;
>  
> @@ -467,6 +472,125 @@ unsigned long mem_cgroup_isolate_pages(u
>  	return nr_taken;
>  }
>  
> +static struct mem_cgroup *
> +mem_cgroup_from_res_counter(struct res_counter *counter)
> +{
> +	return container_of(counter, struct mem_cgroup, res);
> +}
> +
> +/*
> + * Dance down the hierarchy if needed to reclaim memory. We remember the
> + * last child we reclaimed from, so that we don't end up penalizing
> + * one child extensively based on its position in the children list
> + */
> +static int
> +mem_cgroup_hierarchical_reclaim(struct mem_cgroup *mem, gfp_t gfp_mask)
> +{
> +	struct cgroup *cg, *cg_current, *cgroup;
> +	struct mem_cgroup *mem_child;
> +	int ret = 0;
> +
> +	if (try_to_free_mem_cgroup_pages(mem, gfp_mask))
> +		return -ENOMEM;
> +
> +	/*
> +	 * try_to_free_mem_cgroup_pages() might not give us a full
> +	 * picture of reclaim. Some pages are reclaimed and might be
> +	 * moved to swap cache or just unmapped from the cgroup.
> +	 * Check the limit again to see if the reclaim reduced the
> +	 * current usage of the cgroup before giving up
> +	 */
> +	if (res_counter_check_under_limit(&mem->res))
> +		return 0;
> +
> +	/*
> +	 * Scan all children under the mem_cgroup mem
> +	 */
> +	if (!mem->last_scanned_child)
> +		cgroup = list_first_entry(&mem->css.cgroup->children,
> +				struct cgroup, sibling);
> +	else
> +		cgroup = mem->last_scanned_child->css.cgroup;
> +
> +	cg_current = cgroup;
> +
> +	/*
> +	 * We iterate twice, one of it is fundamental list issue, where
> +	 * the elements are inserted using list_add and hence the list
> +	 * behaves like a stack and list_for_entry_safe_from() stops
> +	 * after seeing the first child. The two loops help us work
> +	 * independently of the insertion and it helps us get a full pass at
> +	 * scanning all list entries for reclaim
> +	 */
> +	list_for_each_entry_safe_from(cgroup, cg, &cg_current->parent->children,
> +						 sibling) {
> +		mem_child = mem_cgroup_from_cont(cgroup);
> +
> +		/*
> +		 * Move beyond last scanned child
> +		 */
> +		if (mem_child == mem->last_scanned_child)
> +			continue;
> +
> +		ret = try_to_free_mem_cgroup_pages(mem_child, gfp_mask);
> +		mem->last_scanned_child = mem_child;
> +
> +		if (res_counter_check_under_limit(&mem->res)) {
> +			ret = 0;
> +			goto done;
> +		}
> +	}

Is this safe against cgroup create/remove ? cgroup_mutex is held ?

Thanks,
-Kame

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