memcg: stop using css id

#ifdef CONFIG_MEMCG_KMEM

/*

 * This will be the memcg's index in each cache's ->memcg_params->memcg_caches.

 * There are two main reasons for not using the css_id for this:

 *  1) this works better in sparse environments, where we have a lot of memcgs,

 * The main reason for not using cgroup id for this:

 *  this works better in sparse environments, where we have a lot of memcgs,

 *  but only a few kmem-limited. Or also, if we have, for instance, 200

 *  memcgs, and none but the 200th is kmem-limited, we'd have to have a

 *  200 entry array for that.

 *

 *  2) In order not to violate the cgroup API, we would like to do all memory

 *     allocation in ->create(). At that point, we haven't yet allocated the

 *     css_id. Having a separate index prevents us from messing with the cgroup

 *     core for this

 *

 * The current size of the caches array is stored in

 * memcg_limited_groups_array_size.  It will double each time we have to

 * increase it.

 * cgroups is a reasonable guess. In the future, it could be a parameter or

 * tunable, but that is strictly not necessary.

 *

 * MAX_SIZE should be as large as the number of css_ids. Ideally, we could get

 * MAX_SIZE should be as large as the number of cgrp_ids. Ideally, we could get

 * this constant directly from cgroup, but it is understandable that this is

 * better kept as an internal representation in cgroup.c. In any case, the

 * css_id space is not getting any smaller, and we don't have to necessarily

 * cgrp_id space is not getting any smaller, and we don't have to necessarily

 * increase ours as well if it increases.

 */

#define MEMCG_CACHES_MIN_SIZE 4

#define MEMCG_CACHES_MAX_SIZE 65535

#define MEMCG_CACHES_MAX_SIZE MEM_CGROUP_ID_MAX

/*

 * A lot of the calls to the cache allocation functions are expected to be

	int node;

	size_t size = memcg_size();

	free_css_id(&mem_cgroup_subsys, &memcg->css);

	for_each_node(node)

		free_mem_cgroup_per_zone_info(memcg, node);

	.bind = mem_cgroup_bind,

	.base_cftypes = mem_cgroup_files,

	.early_init = 0,

	.use_id = 1,

};

#ifdef CONFIG_MEMCG_SWAP