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Date: Tue, 31 Aug 2010 12:44:14 +0530
From: Balbir Singh <balbir@...ux.vnet.ibm.com>
To: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc: linux-mm@...ck.org,
"nishimura@....nes.nec.co.jp" <nishimura@....nes.nec.co.jp>,
gthelen@...gle.com, m-ikeda@...jp.nec.com,
"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"menage@...gle.com" <menage@...gle.com>,
"lizf@...fujitsu.com" <lizf@...fujitsu.com>
Subject: Re: [PATCH 2/5] memcg: quick memcg lookup array
* KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> [2010-08-25 17:07:41]:
> From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
>
> Now, memory cgroup has an ID per cgroup and make use of it at
> - hierarchy walk,
> - swap recording.
>
> This patch is for making more use of it. The final purpose is
> to replace page_cgroup->mem_cgroup's pointer to an unsigned short.
>
> This patch caches a pointer of memcg in an array. By this, we
> don't have to call css_lookup() which requires radix-hash walk.
> This saves some amount of memory footprint at lookup memcg via id.
>
> Changelog: 20100825
> - applied comments.
>
> Changelog: 20100811
> - adjusted onto mmotm-2010-08-11
> - fixed RCU related parts.
> - use attach_id() callback.
>
> Changelog: 20100804
> - fixed description in init/Kconfig
>
> Changelog: 20100730
> - fixed rcu_read_unlock() placement.
>
> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
> ---
> init/Kconfig | 10 +++++++
> mm/memcontrol.c | 75 +++++++++++++++++++++++++++++++++++++++++---------------
> 2 files changed, 65 insertions(+), 20 deletions(-)
>
> Index: mmotm-0811/mm/memcontrol.c
> ===================================================================
> --- mmotm-0811.orig/mm/memcontrol.c
> +++ mmotm-0811/mm/memcontrol.c
> @@ -195,6 +195,7 @@ static void mem_cgroup_oom_notify(struct
> */
> struct mem_cgroup {
> struct cgroup_subsys_state css;
> + int valid; /* for checking validness under RCU access.*/
> /*
> * the counter to account for memory usage
> */
> @@ -294,6 +295,29 @@ static bool move_file(void)
> &mc.to->move_charge_at_immigrate);
> }
>
> +/* 0 is unused */
> +static atomic_t mem_cgroup_num;
> +#define NR_MEMCG_GROUPS (CONFIG_MEM_CGROUP_MAX_GROUPS + 1)
> +static struct mem_cgroup *mem_cgroups[NR_MEMCG_GROUPS] __read_mostly;
> +
> +/* Must be called under rcu_read_lock */
> +static struct mem_cgroup *id_to_memcg(unsigned short id)
> +{
> + struct mem_cgroup *mem;
> + /* see mem_cgroup_free() */
> + mem = rcu_dereference_check(mem_cgroups[id], rcu_read_lock_held());
> + if (likely(mem && mem->valid))
> + return mem;
> + return NULL;
> +}
> +
> +static void register_memcg_id(struct mem_cgroup *mem)
> +{
> + int id = css_id(&mem->css);
> + rcu_assign_pointer(mem_cgroups[id], mem);
> + VM_BUG_ON(!mem->valid);
> +}
> +
> /*
> * Maximum loops in mem_cgroup_hierarchical_reclaim(), used for soft
> * limit reclaim to prevent infinite loops, if they ever occur.
> @@ -1847,18 +1871,7 @@ static void mem_cgroup_cancel_charge(str
> * it's concern. (dropping refcnt from swap can be called against removed
> * memcg.)
> */
> -static struct mem_cgroup *mem_cgroup_lookup(unsigned short id)
> -{
> - struct cgroup_subsys_state *css;
>
> - /* ID 0 is unused ID */
> - if (!id)
> - return NULL;
> - css = css_lookup(&mem_cgroup_subsys, id);
> - if (!css)
> - return NULL;
> - return container_of(css, struct mem_cgroup, css);
> -}
>
> struct mem_cgroup *try_get_mem_cgroup_from_page(struct page *page)
> {
> @@ -1879,7 +1892,7 @@ struct mem_cgroup *try_get_mem_cgroup_fr
> ent.val = page_private(page);
> id = lookup_swap_cgroup(ent);
> rcu_read_lock();
> - mem = mem_cgroup_lookup(id);
> + mem = id_to_memcg(id);
> if (mem && !css_tryget(&mem->css))
> mem = NULL;
> rcu_read_unlock();
> @@ -2231,7 +2244,7 @@ __mem_cgroup_commit_charge_swapin(struct
>
> id = swap_cgroup_record(ent, 0);
> rcu_read_lock();
> - memcg = mem_cgroup_lookup(id);
> + memcg = id_to_memcg(id);
> if (memcg) {
> /*
> * This recorded memcg can be obsolete one. So, avoid
> @@ -2240,9 +2253,10 @@ __mem_cgroup_commit_charge_swapin(struct
> if (!mem_cgroup_is_root(memcg))
> res_counter_uncharge(&memcg->memsw, PAGE_SIZE);
> mem_cgroup_swap_statistics(memcg, false);
> + rcu_read_unlock();
> mem_cgroup_put(memcg);
> - }
> - rcu_read_unlock();
> + } else
> + rcu_read_unlock();
> }
> /*
> * At swapin, we may charge account against cgroup which has no tasks.
> @@ -2495,7 +2509,7 @@ void mem_cgroup_uncharge_swap(swp_entry_
>
> id = swap_cgroup_record(ent, 0);
> rcu_read_lock();
> - memcg = mem_cgroup_lookup(id);
> + memcg = id_to_memcg(id);
> if (memcg) {
> /*
> * We uncharge this because swap is freed.
> @@ -2504,9 +2518,10 @@ void mem_cgroup_uncharge_swap(swp_entry_
> if (!mem_cgroup_is_root(memcg))
> res_counter_uncharge(&memcg->memsw, PAGE_SIZE);
> mem_cgroup_swap_statistics(memcg, false);
> + rcu_read_unlock();
> mem_cgroup_put(memcg);
> - }
> - rcu_read_unlock();
> + } else
> + rcu_read_unlock();
> }
>
> /**
> @@ -4010,6 +4025,9 @@ static struct mem_cgroup *mem_cgroup_all
> struct mem_cgroup *mem;
> int size = sizeof(struct mem_cgroup);
>
> + if (atomic_read(&mem_cgroup_num) == NR_MEMCG_GROUPS)
> + return NULL;
> +
> /* Can be very big if MAX_NUMNODES is very big */
> if (size < PAGE_SIZE)
> mem = kmalloc(size, GFP_KERNEL);
> @@ -4020,6 +4038,7 @@ static struct mem_cgroup *mem_cgroup_all
> return NULL;
>
> memset(mem, 0, size);
> + mem->valid = 1;
> mem->stat = alloc_percpu(struct mem_cgroup_stat_cpu);
> if (!mem->stat) {
> if (size < PAGE_SIZE)
> @@ -4049,6 +4068,7 @@ static void __mem_cgroup_free(struct mem
> mem_cgroup_remove_from_trees(mem);
> free_css_id(&mem_cgroup_subsys, &mem->css);
>
> + atomic_dec(&mem_cgroup_num);
> for_each_node_state(node, N_POSSIBLE)
> free_mem_cgroup_per_zone_info(mem, node);
>
> @@ -4059,6 +4079,19 @@ static void __mem_cgroup_free(struct mem
> vfree(mem);
> }
>
> +static void mem_cgroup_free(struct mem_cgroup *mem)
> +{
> + /* No more lookup */
> + mem->valid = 0;
> + rcu_assign_pointer(mem_cgroups[css_id(&mem->css)], NULL);
> + /*
> + * Because we call vfree() etc...use synchronize_rcu() rather than
> + * call_rcu();
> + */
> + synchronize_rcu();
> + __mem_cgroup_free(mem);
> +}
> +
> static void mem_cgroup_get(struct mem_cgroup *mem)
> {
> atomic_inc(&mem->refcnt);
> @@ -4068,7 +4101,7 @@ static void __mem_cgroup_put(struct mem_
> {
> if (atomic_sub_and_test(count, &mem->refcnt)) {
> struct mem_cgroup *parent = parent_mem_cgroup(mem);
> - __mem_cgroup_free(mem);
> + mem_cgroup_free(mem);
> if (parent)
> mem_cgroup_put(parent);
> }
> @@ -4189,9 +4222,11 @@ mem_cgroup_create(struct cgroup_subsys *
> atomic_set(&mem->refcnt, 1);
> mem->move_charge_at_immigrate = 0;
> mutex_init(&mem->thresholds_lock);
> + atomic_inc(&mem_cgroup_num);
> + register_memcg_id(mem);
> return &mem->css;
> free_out:
> - __mem_cgroup_free(mem);
> + mem_cgroup_free(mem);
> root_mem_cgroup = NULL;
> return ERR_PTR(error);
> }
> Index: mmotm-0811/init/Kconfig
> ===================================================================
> --- mmotm-0811.orig/init/Kconfig
> +++ mmotm-0811/init/Kconfig
> @@ -594,6 +594,16 @@ config CGROUP_MEM_RES_CTLR_SWAP
> Now, memory usage of swap_cgroup is 2 bytes per entry. If swap page
> size is 4096bytes, 512k per 1Gbytes of swap.
>
> +config MEM_CGROUP_MAX_GROUPS
> + int "Maximum number of memory cgroups on a system"
> + range 1 65535
> + default 8192 if 64BIT
> + default 2048 if 32BIT
> + help
> + Memory cgroup has limitation of the number of groups created.
> + Please select your favorite value. The more you allow, the more
> + memory(a pointer per group) will be consumed.
> +
Looks good, quick thought - should we expost memcg->id to user space
through a config file? I don't see any reason at this point, unless we
do it for all controllers.
--
Three Cheers,
Balbir
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