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Date: Fri, 16 Jan 2009 10:38:10 +0900 From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> To: Li Zefan <lizf@...fujitsu.com> Cc: "linux-mm@...ck.org" <linux-mm@...ck.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "menage@...gle.com" <menage@...gle.com>, "balbir@...ux.vnet.ibm.com" <balbir@...ux.vnet.ibm.com>, "nishimura@....nes.nec.co.jp" <nishimura@....nes.nec.co.jp> Subject: Re: [PATCH 3/4] memcg: hierarchical reclaim by CSS ID On Fri, 16 Jan 2009 09:29:48 +0800 Li Zefan <lizf@...fujitsu.com> 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. 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. 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@...ck.org. For more info on Linux MM, > see: http://www.linux-mm.org/ . > Don't email: <a href=mailto:"dont@...ck.org"> email@...ck.org </a> > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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