Re: [mmotm][experimental][PATCH] coalescing charge

[Daisuke Nishimura]

On Wed, 2 Sep 2009 18:29:23 +0900, KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxx>
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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