From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx102.postini.com [74.125.245.102]) by kanga.kvack.org (Postfix) with SMTP id AD99C6B0005 for ; Tue, 9 Apr 2013 03:53:09 -0400 (EDT) Message-ID: <5163C90E.8040602@parallels.com> Date: Tue, 9 Apr 2013 11:53:50 +0400 From: Glauber Costa MIME-Version: 1.0 Subject: Re: [PATCH 13/12] memcg: don't need memcg->memcg_name References: <5162648B.9070802@huawei.com> <51626584.7050405@huawei.com> <5163868B.3020905@jp.fujitsu.com> <5163887D.1040809@huawei.com> In-Reply-To: <5163887D.1040809@huawei.com> Content-Type: text/plain; charset="GB2312" Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Li Zefan Cc: Kamezawa Hiroyuki , Andrew Morton , Tejun Heo , Johannes Weiner , LKML , Cgroups , linux-mm@kvack.org On 04/09/2013 07:18 AM, Li Zefan wrote: >>> @@ -5188,12 +5154,28 @@ static int mem_cgroup_dangling_read(struct cgroup *cont, struct cftype *cft, >>> struct seq_file *m) >>> { >>> struct mem_cgroup *memcg; >>> + char *memcg_name; >>> + int ret; >>> + >>> + /* >>> + * cgroup.c will do page-sized allocations most of the time, >>> + * so we'll just follow the pattern. Also, __get_free_pages >>> + * is a better interface than kmalloc for us here, because >>> + * we'd like this memory to be always billed to the root cgroup, >>> + * not to the process removing the memcg. While kmalloc would >>> + * require us to wrap it into memcg_stop/resume_kmem_account, >>> + * with __get_free_pages we just don't pass the memcg flag. >>> + */ >>> + memcg_name = (char *)__get_free_pages(GFP_KERNEL, 0); >>> + if (!memcg_name) >>> + return -ENOMEM; >>> >>> mutex_lock(&dangling_memcgs_mutex); >>> >>> list_for_each_entry(memcg, &dangling_memcgs, dead) { >>> - if (memcg->memcg_name) >>> - seq_printf(m, "%s:\n", memcg->memcg_name); >>> + ret = cgroup_path(memcg->css.cgroup, memcg_name, PAGE_SIZE); >>> + if (!ret) >>> + seq_printf(m, "%s:\n", memcg_name); >>> else >>> seq_printf(m, "%p (name lost):\n", memcg); >>> >> >> I'm sorry for dawm question ...when this error happens ? >> We may get ENAMETOOLONG even with PAGE_SIZE(>=4096bytes) buffer ? >> > > It does no harm to check the return value, and we don't have to > worry about if cgroup_path() will be changed to return some other > errno like ENOMEM in the future. > I feel more comfortable with the check as well. This is a debugging interface after all. People tend to resort to this when things go wrong. So at this point the less assumptions we make, the better. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org