From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail144.messagelabs.com (mail144.messagelabs.com [216.82.254.51]) by kanga.kvack.org (Postfix) with SMTP id 73E826B0055 for ; Thu, 15 Jan 2009 20:49:47 -0500 (EST) Message-ID: <496FE791.9030208@cn.fujitsu.com> Date: Fri, 16 Jan 2009 09:49:05 +0800 From: Li Zefan MIME-Version: 1.0 Subject: Re: [PATCH 3/4] memcg: hierarchical reclaim by CSS ID References: <20090115192120.9956911b.kamezawa.hiroyu@jp.fujitsu.com> <20090115192943.7c1df53a.kamezawa.hiroyu@jp.fujitsu.com> <496FE30C.1090300@cn.fujitsu.com> <20090116103810.5ef55cc3.kamezawa.hiroyu@jp.fujitsu.com> In-Reply-To: <20090116103810.5ef55cc3.kamezawa.hiroyu@jp.fujitsu.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org To: KAMEZAWA Hiroyuki Cc: "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" , "menage@google.com" , "balbir@linux.vnet.ibm.com" , "nishimura@mxp.nes.nec.co.jp" List-ID: KAMEZAWA Hiroyuki wrote: > On Fri, 16 Jan 2009 09:29:48 +0800 > Li Zefan wrote: > >>> /* >>> - * Dance down the hierarchy if needed to reclaim memory. We remember the >>> - * last child we reclaimed from, so that we don't end up penalizing >>> - * one child extensively based on its position in the children list. >>> + * Visit the first child (need not be the first child as per the ordering >>> + * of the cgroup list, since we track last_scanned_child) of @mem and use >>> + * that to reclaim free pages from. >>> + */ >>> +static struct mem_cgroup * >>> +mem_cgroup_select_victim(struct mem_cgroup *root_mem) >>> +{ >>> + struct mem_cgroup *ret = NULL; >>> + struct cgroup_subsys_state *css; >>> + int nextid, found; >>> + >>> + if (!root_mem->use_hierarchy) { >>> + spin_lock(&root_mem->reclaim_param_lock); >>> + root_mem->scan_age++; >>> + spin_unlock(&root_mem->reclaim_param_lock); >>> + css_get(&root_mem->css); >>> + ret = root_mem; >>> + } >>> + >>> + while (!ret) { >>> + rcu_read_lock(); >>> + nextid = root_mem->last_scanned_child + 1; >>> + css = css_get_next(&mem_cgroup_subsys, nextid, &root_mem->css, >>> + &found); >>> + if (css && css_is_populated(css) && css_tryget(css)) >> I don't see why you need to check css_is_populated(css) ? >> > > Main reason is for sanity. I don't like to hold css->refcnt of not populated css. I think this is a rare case. It's just a very short period when a cgroup is being created but not yet fully created. > Second reason is for avoinding unnecessary calls to try_to_free_pages(), > it's heavy. I should also add mem->res.usage == 0 case for skipping but not yet. > And if mem->res.usage == 0 is checked, css_is_popuated() is just redundant. > THanks, > -Kame > >>> + ret = container_of(css, struct mem_cgroup, css); >>> + >>> + rcu_read_unlock(); >>> + /* Updates scanning parameter */ >>> + spin_lock(&root_mem->reclaim_param_lock); >>> + if (!css) { >>> + /* this means start scan from ID:1 */ >>> + root_mem->last_scanned_child = 0; >>> + root_mem->scan_age++; >>> + } else >>> + root_mem->last_scanned_child = found; >>> + spin_unlock(&root_mem->reclaim_param_lock); >>> + } >>> + >>> + return ret; >>> +} >>> + -- 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