Re: [RFC] [PATCH 3/4] Reclaim from groups over their soft limit under memory pressure

[yamamoto@valinux.co.jp (YAMAMOTO Takashi)]

> +/*
> + * Free all control groups, which are over their soft limit
> + */
> +unsigned long mem_cgroup_pushback_groups_over_soft_limit(struct zone **zones,
> +								gfp_t gfp_mask)
> +{
> +	struct mem_cgroup *mem;
> +	unsigned long nr_pages;
> +	long long nr_bytes_over_sl;
> +	unsigned long ret = 0;
> +	unsigned long flags;
> +	struct list_head reclaimed_groups;
>  
> +	INIT_LIST_HEAD(&reclaimed_groups);
> +	read_lock_irqsave(&mem_cgroup_sl_list_lock, flags);
> +	while (!list_empty(&mem_cgroup_sl_exceeded_list)) {
> +		mem = list_first_entry(&mem_cgroup_sl_exceeded_list,
> +				struct mem_cgroup, sl_exceeded_list);
> +		list_move(&mem->sl_exceeded_list, &reclaimed_groups);
> +		read_unlock_irqrestore(&mem_cgroup_sl_list_lock, flags);
> +
> +		nr_bytes_over_sl = res_counter_sl_excess(&mem->res);
> +		if (nr_bytes_over_sl <= 0)
> +			goto next;
> +		nr_pages = (nr_bytes_over_sl >> PAGE_SHIFT);
> +		ret += try_to_free_mem_cgroup_pages(mem, gfp_mask, nr_pages,
> +							zones);
> +next:
> +		read_lock_irqsave(&mem_cgroup_sl_list_lock, flags);
> +	}

what prevents the cgroup 'mem' from disappearing while we are dropping
mem_cgroup_sl_list_lock?

YAMAMOTO Takashi

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