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Date: Thu, 3 Sep 2009 14:17:27 +0900
From: Daisuke Nishimura <nishimura@....nes.nec.co.jp>
To: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc: nishimura@....nes.nec.co.jp,
"linux-mm@...ck.org" <linux-mm@...ck.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"balbir@...ux.vnet.ibm.com" <balbir@...ux.vnet.ibm.com>,
"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>
Subject: Re: [mmotm][experimental][PATCH] coalescing charge
On Wed, 2 Sep 2009 18:29:23 +0900, KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> wrote:
> I'm sorry that I'll be absent tomorrow. This is dump of current code.
> IMHO, this version is enough simple.
>
> My next target is css's refcnt per page. I think we never need it...
>
hmm, maybe.
> =
> This is a code for batched charging using percpu cache.
> At charge, memcg charges 64pages and remember it in percpu cache.
> Because it's cache, drain/flushed if necessary.
>
> This version uses public percpu area , not per-memcg percpu area.
> 2 benefits of public percpu area.
> 1. Sum of stocked charge in the system is limited to # of cpus
> not to the number of memcg. This shows better synchonization.
> 2. drain code for flush/cpuhotplug is very easy (and quick)
>
> The most important point of this patch is that we never touch res_counter
> in fast path. The res_counter is system-wide shared counter which is modified
> very frequently. We shouldn't touch it as far as we can for avoid false sharing.
>
> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
It looks basically good. I'll do some tests with all patches applied.
I have some comments inlined.
> ---
> mm/memcontrol.c | 93 ++++++++++++++++++++++++++++++++++++++++++++++++++++----
> 1 file changed, 88 insertions(+), 5 deletions(-)
>
> Index: mmotm-2.6.31-Aug27/mm/memcontrol.c
> ===================================================================
> --- mmotm-2.6.31-Aug27.orig/mm/memcontrol.c
> +++ mmotm-2.6.31-Aug27/mm/memcontrol.c
> @@ -275,6 +275,7 @@ enum charge_type {
> static void mem_cgroup_get(struct mem_cgroup *mem);
> static void mem_cgroup_put(struct mem_cgroup *mem);
> static struct mem_cgroup *parent_mem_cgroup(struct mem_cgroup *mem);
> +static void drain_all_stock(void);
>
> static struct mem_cgroup_per_zone *
> mem_cgroup_zoneinfo(struct mem_cgroup *mem, int nid, int zid)
> @@ -1136,6 +1137,8 @@ static int mem_cgroup_hierarchical_recla
> victim = mem_cgroup_select_victim(root_mem);
> if (victim == root_mem) {
> loop++;
> + if (loop >= 1)
> + drain_all_stock();
> if (loop >= 2) {
> /*
> * If we have not been able to reclaim
> @@ -1253,6 +1256,79 @@ done:
> unlock_page_cgroup(pc);
> }
>
> +#define CHARGE_SIZE (64 * PAGE_SIZE)
> +struct memcg_stock_pcp {
> + struct mem_cgroup *from;
> + int charge;
> +};
> +DEFINE_PER_CPU(struct memcg_stock_pcp, memcg_stock);
> +
It might be better to add "static".
> +static bool consume_stock(struct mem_cgroup *mem)
> +{
> + struct memcg_stock_pcp *stock;
> + bool ret = true;
> +
> + stock = &get_cpu_var(memcg_stock);
> + if (mem == stock->from && stock->charge)
> + stock->charge -= PAGE_SIZE;
> + else
> + ret = false;
> + put_cpu_var(memcg_stock);
> + return ret;
> +}
> +
> +static void drain_stock(struct memcg_stock_pcp *stock)
> +{
> + struct mem_cgroup *old = stock->from;
> +
> + if (stock->charge) {
> + res_counter_uncharge(&old->res, stock->charge);
> + if (do_swap_account)
> + res_counter_uncharge(&old->memsw, stock->charge);
> + }
> + stock->from = NULL;
We must clear stock->charge too.
> +}
> +
> +static void drain_local_stock(struct work_struct *dummy)
> +{
> + struct memcg_stock_pcp *stock = &get_cpu_var(memcg_stock);
> + drain_stock(stock);
> + put_cpu_var(memcg_stock);
> +}
> +
> +static void refill_stock(struct mem_cgroup *mem, int val)
> +{
> + struct memcg_stock_pcp *stock = &get_cpu_var(memcg_stock);
> +
> + if (stock->from != mem) {
> + drain_stock(stock);
> + stock->from = mem;
> + }
> + stock->charge = val;
> + put_cpu_var(memcg_stock);
> +}
> +
> +static void drain_all_stock(void)
> +{
> + schedule_on_each_cpu(drain_local_stock);
> +}
> +
> +static int __cpuinit memcg_stock_cpu_callback(struct notifier_block *nb,
> + unsigned long action,
> + void *hcpu)
> +{
> +#ifdef CONFIG_HOTPLUG_CPU
> + int cpu = (unsigned long)*hcpu;
'*' isn't needed.
> + struct memcg_stock_pcp *stock;
> +
> + if (action != CPU_DEAD)
> + return NOTIFY_OK;
> + stock = per_cpu(memcg_stock, cpu);
'&' is needed.
> + drain_stock(stock);
> +#endif
> + return NOTIFY_OK;
> +}
> +
> /*
> * Unlike exported interface, "oom" parameter is added. if oom==true,
> * oom-killer can be invoked.
> @@ -1288,23 +1364,25 @@ static int __mem_cgroup_try_charge(struc
> return 0;
>
> VM_BUG_ON(css_is_removed(&mem->css));
> + if (mem_cgroup_is_root(mem))
> + goto done;
> + if (consume_stock(mem))
> + goto charged;
>
> while (1) {
> int ret = 0;
> unsigned long flags = 0;
>
> - if (mem_cgroup_is_root(mem))
> - goto done;
> - ret = res_counter_charge(&mem->res, PAGE_SIZE, &fail_res);
> + ret = res_counter_charge(&mem->res, CHARGE_SIZE, &fail_res);
> if (likely(!ret)) {
> if (!do_swap_account)
> break;
> - ret = res_counter_charge(&mem->memsw, PAGE_SIZE,
> + ret = res_counter_charge(&mem->memsw, CHARGE_SIZE,
> &fail_res);
> if (likely(!ret))
> break;
> /* mem+swap counter fails */
> - res_counter_uncharge(&mem->res, PAGE_SIZE);
> + res_counter_uncharge(&mem->res, CHARGE_SIZE);
> flags |= MEM_CGROUP_RECLAIM_NOSWAP;
> mem_over_limit = mem_cgroup_from_res_counter(fail_res,
> memsw);
> @@ -1342,6 +1420,9 @@ static int __mem_cgroup_try_charge(struc
> goto nomem;
> }
> }
> + refill_stock(mem, CHARGE_SIZE - PAGE_SIZE);
> +
> +charged:
> /*
> * Insert ancestor (and ancestor's ancestors), to softlimit RB-tree.
> * if they exceeds softlimit.
> @@ -2448,6 +2529,7 @@ move_account:
> goto out;
> /* This is for making all *used* pages to be on LRU. */
> lru_add_drain_all();
> + drain_all_stock();
> ret = 0;
> for_each_node_state(node, N_HIGH_MEMORY) {
> for (zid = 0; !ret && zid < MAX_NR_ZONES; zid++) {
> @@ -3166,6 +3248,7 @@ mem_cgroup_create(struct cgroup_subsys *
> root_mem_cgroup = mem;
> if (mem_cgroup_soft_limit_tree_init())
> goto free_out;
> + hotcpu_notifier(memcg_stock_cpu_callback, 0);
>
We should include cpu.h to use hotcpu_notifier().
> } else {
> parent = mem_cgroup_from_cont(cont->parent);
>
Thanks,
Daisuke Nishimura.
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