Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760161AbZJHX5k (ORCPT ); Thu, 8 Oct 2009 19:57:40 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1760093AbZJHX5h (ORCPT ); Thu, 8 Oct 2009 19:57:37 -0400 Received: from fgwmail6.fujitsu.co.jp ([192.51.44.36]:60893 "EHLO fgwmail6.fujitsu.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1760146AbZJHX5g (ORCPT ); Thu, 8 Oct 2009 19:57:36 -0400 X-SecurityPolicyCheck-FJ: OK by FujitsuOutboundMailChecker v1.3.1 Date: Fri, 9 Oct 2009 08:54:35 +0900 From: KAMEZAWA Hiroyuki To: Andrew Morton Cc: "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" , "balbir@linux.vnet.ibm.com" , "nishimura@mxp.nes.nec.co.jp" Subject: Re: [PATCH 2/2] memcg: coalescing charges per cpu Message-Id: <20091009085435.889c9a26.kamezawa.hiroyu@jp.fujitsu.com> In-Reply-To: <20091008152620.e81d6209.akpm@linux-foundation.org> References: <20091002135531.3b5abf5c.kamezawa.hiroyu@jp.fujitsu.com> <20091002140343.ae63e932.kamezawa.hiroyu@jp.fujitsu.com> <20091008152620.e81d6209.akpm@linux-foundation.org> Organization: FUJITSU Co. LTD. X-Mailer: Sylpheed 2.5.0 (GTK+ 2.10.14; i686-pc-mingw32) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 7820 Lines: 254 On Thu, 8 Oct 2009 15:26:20 -0700 Andrew Morton wrote: > On Fri, 2 Oct 2009 14:03:43 +0900 > KAMEZAWA Hiroyuki wrote: > > > From: KAMEZAWA Hiroyuki > > > > This is a patch for coalescing access to res_counter at charging by > > percpu caching. At charge, memcg charges 64pages and remember it in > > percpu cache. Because it's cache, drain/flush is done if necessary. > > > > This version uses public percpu area. > > 2 benefits of using 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 avoiding > > false sharing. > > > > ... > > > > +/* size of first charge trial. "32" comes from vmscan.c's magic value */ > > +#define CHARGE_SIZE (32 * PAGE_SIZE) > > +struct memcg_stock_pcp { > > + struct mem_cgroup *cached; > > + int charge; > > + struct work_struct work; > > +}; > > +static DEFINE_PER_CPU(struct memcg_stock_pcp, memcg_stock); > > +static DEFINE_MUTEX(memcg_drain_mutex); > > + > > +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->cached && stock->charge) > > + stock->charge -= PAGE_SIZE; > > + else > > + ret = false; > > + put_cpu_var(memcg_stock); > > + return ret; > > +} > > It's unobvious what the return value from this function means. A nice > comment would help. will do. > > > +static void drain_stock(struct memcg_stock_pcp *stock) > > +{ > > + struct mem_cgroup *old = stock->cached; > > + > > + if (stock->charge) { > > + res_counter_uncharge(&old->res, stock->charge); > > + if (do_swap_account) > > + res_counter_uncharge(&old->memsw, stock->charge); > > + } > > + stock->cached = NULL; > > + stock->charge = 0; > > +} > > + > > +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); > > +} > > drain_local_stock() is only ever run by a thread which is pinned to a > particular CPU, so we can use plain old __get_cpu_var() here and remove > the put_cpu_var(), methinks. If this is done, a comment shuold be > added explaining why we can use that optimisation. > Ok. I'll try and test that. > > +static void refill_stock(struct mem_cgroup *mem, int val) > > +{ > > + struct memcg_stock_pcp *stock = &get_cpu_var(memcg_stock); > > + > > + if (stock->cached != mem) { > > + drain_stock(stock); > > + stock->cached = mem; > > + } > > + stock->charge += val; > > + put_cpu_var(memcg_stock); > > +} > > + > > +static void drain_all_stock_async(void) > > +{ > > + int cpu; > > + /* Contention means someone tries to flush. */ > > + if (!mutex_trylock(&memcg_drain_mutex)) > > + return; > > Any time I see a trylock I ask "hm, what happens when it fails - what > are the consequences and how to we later rerun the aborted operation". > I'll add more comments. > That's unobvious here and merits a comment. > > > + for_each_online_cpu(cpu) { > > Did we need get_online_cpus() here? > Ahhhh, yes. It's necessary. > > + struct memcg_stock_pcp *stock = &per_cpu(memcg_stock, cpu); > > + if (work_pending(&stock->work)) > > + continue; > > + INIT_WORK(&stock->work, drain_local_stock); > > + schedule_work_on(cpu, &stock->work); > > + } > > + mutex_unlock(&memcg_drain_mutex); > > + /* We don't wait for flush_work */ > > +} > > + > > +static void drain_all_stock_sync(void) > > +{ > > + /* called when force_empty is called */ > > + mutex_lock(&memcg_drain_mutex); > > + schedule_on_each_cpu(drain_local_stock); > > + mutex_unlock(&memcg_drain_mutex); > > +} > > In fact it would be nice were each of these functions to have a brief > note describing their role. > Okay. I'll add. > > +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; > > + struct memcg_stock_pcp *stock; > > + > > + if (action != CPU_DEAD) > > + return NOTIFY_OK; > > + stock = &per_cpu(memcg_stock, cpu); > > + drain_stock(stock); > > +#endif > > + return NOTIFY_OK; > > +} > > Is the ifdef needed? Using hotcpu_notifier() should cause this entire > function to disappear from vmlinux when CONFIG_HOTPLUG_CPU=n. > Ah, I didn't notice that. I'll try. Thank you. Regards, -Kame > > /* > > * Unlike exported interface, "oom" parameter is added. if oom==true, > > * oom-killer can be invoked. > > @@ -1269,6 +1370,7 @@ static int __mem_cgroup_try_charge(struc > > struct mem_cgroup *mem, *mem_over_limit; > > int nr_retries = MEM_CGROUP_RECLAIM_RETRIES; > > struct res_counter *fail_res; > > + int csize = CHARGE_SIZE; > > > > if (unlikely(test_thread_flag(TIF_MEMDIE))) { > > /* Don't account this! */ > > @@ -1293,23 +1395,25 @@ 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; > > > > 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); > > + if (consume_stock(mem)) > > + goto charged; > > + > > + ret = res_counter_charge(&mem->res, csize, &fail_res); > > if (likely(!ret)) { > > if (!do_swap_account) > > break; > > - ret = res_counter_charge(&mem->memsw, PAGE_SIZE, > > - &fail_res); > > + ret = res_counter_charge(&mem->memsw, csize, &fail_res); > > if (likely(!ret)) > > break; > > /* mem+swap counter fails */ > > - res_counter_uncharge(&mem->res, PAGE_SIZE); > > + res_counter_uncharge(&mem->res, csize); > > flags |= MEM_CGROUP_RECLAIM_NOSWAP; > > mem_over_limit = mem_cgroup_from_res_counter(fail_res, > > memsw); > > @@ -1318,6 +1422,11 @@ static int __mem_cgroup_try_charge(struc > > mem_over_limit = mem_cgroup_from_res_counter(fail_res, > > res); > > > > + /* reduce request size and retry */ > > + if (csize > PAGE_SIZE) { > > + csize = PAGE_SIZE; > > + continue; > > + } > > if (!(gfp_mask & __GFP_WAIT)) > > goto nomem; > > > > @@ -1347,6 +1456,9 @@ static int __mem_cgroup_try_charge(struc > > goto nomem; > > } > > } > > + if (csize > PAGE_SIZE) > > + refill_stock(mem, csize - PAGE_SIZE); > > +charged: > > /* > > * Insert ancestor (and ancestor's ancestors), to softlimit RB-tree. > > * if they exceeds softlimit. > > @@ -2463,6 +2575,7 @@ move_account: > > goto out; > > /* This is for making all *used* pages to be on LRU. */ > > lru_add_drain_all(); > > + drain_all_stock_sync(); > > ret = 0; > > for_each_node_state(node, N_HIGH_MEMORY) { > > for (zid = 0; !ret && zid < MAX_NR_ZONES; zid++) { > > @@ -3181,6 +3294,7 @@ 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); > > > > } else { > > parent = mem_cgroup_from_cont(cont->parent); > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/