Re: [RFC][mm] [PATCH 3/4] Memory cgroup hierarchical reclaim (v2)

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

On Sat, 08 Nov 2008 14:41:00 +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 |  152 +++++++++++++++++++++++++++++++++++++++++++++++---------
>  1 file changed, 128 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	2008-11-08 14:09:32.000000000 +0530
> +++ linux-2.6.28-rc2-balbir/mm/memcontrol.c	2008-11-08 14:09:32.000000000 +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 +472,124 @@ 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.
> + *
> + * root_mem is the original ancestor that we've been reclaim from.
> + */
> +static int mem_cgroup_hierarchical_reclaim(struct mem_cgroup *mem,
> +						struct mem_cgroup *root_mem,
> +						gfp_t gfp_mask)
> +{
> +	struct cgroup *cg_current, *cgroup;
> +	struct mem_cgroup *mem_child;
> +	int ret = 0;
> +
> +	/*
> +	 * Reclaim unconditionally and don't check for return value.
> +	 * We need to reclaim in the current group and down the tree.
> +	 * One might think about checking for children before reclaiming,
> +	 * but there might be left over accounting, even after children
> +	 * have left.
> +	 */
> +	try_to_free_mem_cgroup_pages(mem, gfp_mask);
> +
> +	if (res_counter_check_under_limit(&root_mem->res))
> +		return 0;
> +
> +	if (list_empty(&mem->css.cgroup->children))
> +		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;
> +

Who guarantee this last_scan_child is accessible at this point ?

Thanks,
-Kame
> +	cg_current = cgroup;
> +	cgroup_lock();
> +
> +	do {
> +		struct list_head *next;
> +
> +		mem_child = mem_cgroup_from_cont(cgroup);
> +		cgroup_unlock();
> +
> +		ret = mem_cgroup_hierarchical_reclaim(mem_child, root_mem,
> +							gfp_mask);
> +		mem->last_scanned_child = mem_child;
> +
> +		cgroup_lock();
> +		if (res_counter_check_under_limit(&root_mem->res)) {
> +			ret = 0;
> +			goto done;
> +		}
> +
> +		/*
> +		 * Since we gave up the lock, it is time to
> +		 * start from last cgroup
> +		 */
> +		cgroup = mem->last_scanned_child->css.cgroup;
> +		next = cgroup->sibling.next;
> +
> +		if (next == &cg_current->parent->children)
> +			cgroup = list_first_entry(&mem->css.cgroup->children,
> +							struct cgroup, sibling);
> +		else
> +			cgroup = container_of(next, struct cgroup, sibling);
> +	} while (cgroup != cg_current);
> +
> +done:
> +	cgroup_unlock();
> +	return ret;
> +}
> +
> +/*
> + * Charge memory cgroup mem and check if it is over its limit. If so, reclaim
> + * from mem.
> + */
> +static int mem_cgroup_charge_and_reclaim(struct mem_cgroup *mem, gfp_t gfp_mask)
> +{
> +	int ret = 0;
> +	unsigned long nr_retries = MEM_CGROUP_RECLAIM_RETRIES;
> +	struct res_counter *fail_res;
> +	struct mem_cgroup *mem_over_limit;
> +
> +	while (unlikely(res_counter_charge(&mem->res, PAGE_SIZE, &fail_res))) {
> +		if (!(gfp_mask & __GFP_WAIT))
> +			goto out;
> +
> +		/*
> +		 * Is one of our ancestors over their limit?
> +		 */
> +		if (fail_res)
> +			mem_over_limit = mem_cgroup_from_res_counter(fail_res);
> +		else
> +			mem_over_limit = mem;
> +
> +		ret = mem_cgroup_hierarchical_reclaim(mem_over_limit,
> +							mem_over_limit,
> +							gfp_mask);
> +
> +		if (!nr_retries--) {
> +			mem_cgroup_out_of_memory(mem, gfp_mask);
> +			goto out;
> +		}
> +	}
> +out:
> +	return ret;
> +}
>  
>  /**
>   * mem_cgroup_try_charge - get charge of PAGE_SIZE.
> @@ -484,8 +607,7 @@ int mem_cgroup_try_charge(struct mm_stru
>  			gfp_t gfp_mask, struct mem_cgroup **memcg)
>  {
>  	struct mem_cgroup *mem;
> -	int nr_retries = MEM_CGROUP_RECLAIM_RETRIES;
> -	struct res_counter *fail_res;
> +
>  	/*
>  	 * We always charge the cgroup the mm_struct belongs to.
>  	 * The mm_struct's mem_cgroup changes on task migration if the
> @@ -510,29 +632,9 @@ int mem_cgroup_try_charge(struct mm_stru
>  		css_get(&mem->css);
>  	}
>  
> +	if (mem_cgroup_charge_and_reclaim(mem, gfp_mask))
> +		goto nomem;
>  
> -	while (unlikely(res_counter_charge(&mem->res, PAGE_SIZE, &fail_res))) {
> -		if (!(gfp_mask & __GFP_WAIT))
> -			goto nomem;
> -
> -		if (try_to_free_mem_cgroup_pages(mem, gfp_mask))
> -			continue;
> -
> -		/*
> -		 * 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))
> -			continue;
> -
> -		if (!nr_retries--) {
> -			mem_cgroup_out_of_memory(mem, gfp_mask);
> -			goto nomem;
> -		}
> -	}
>  	return 0;
>  nomem:
>  	css_put(&mem->css);
> @@ -1195,6 +1297,8 @@ mem_cgroup_create(struct cgroup_subsys *
>  		if (alloc_mem_cgroup_per_zone_info(mem, node))
>  			goto free_out;
>  
> +	mem->last_scanned_child = NULL;
> +
>  	return &mem->css;
>  free_out:
>  	for_each_node_state(node, N_POSSIBLE)
> _
> 
> -- 
> 	Balbir
> --
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