From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx148.postini.com [74.125.245.148]) by kanga.kvack.org (Postfix) with SMTP id 6068C6B0073 for ; Tue, 29 May 2012 11:58:43 -0400 (EDT) Message-ID: <4FC4F1A7.2010206@parallels.com> Date: Tue, 29 May 2012 19:56:23 +0400 From: Glauber Costa MIME-Version: 1.0 Subject: Re: [PATCH v3 13/28] slub: create duplicate cache References: <1337951028-3427-1-git-send-email-glommer@parallels.com> <1337951028-3427-14-git-send-email-glommer@parallels.com> In-Reply-To: Content-Type: text/plain; charset="ISO-8859-1"; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Christoph Lameter Cc: linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, linux-mm@kvack.org, kamezawa.hiroyu@jp.fujitsu.com, Tejun Heo , Li Zefan , Greg Thelen , Suleiman Souhlal , Michal Hocko , Johannes Weiner , devel@openvz.org, David Rientjes , Pekka Enberg On 05/29/2012 06:36 PM, Christoph Lameter wrote: > On Fri, 25 May 2012, Glauber Costa wrote: > >> index dacd1fb..4689034 100644 >> --- a/mm/memcontrol.c >> +++ b/mm/memcontrol.c >> @@ -467,6 +467,23 @@ struct cg_proto *tcp_proto_cgroup(struct mem_cgroup *memcg) >> EXPORT_SYMBOL(tcp_proto_cgroup); >> #endif /* CONFIG_INET */ >> >> +char *mem_cgroup_cache_name(struct mem_cgroup *memcg, struct kmem_cache *cachep) >> +{ >> + char *name; >> + struct dentry *dentry; >> + >> + rcu_read_lock(); >> + dentry = rcu_dereference(memcg->css.cgroup->dentry); >> + rcu_read_unlock(); >> + >> + BUG_ON(dentry == NULL); >> + >> + name = kasprintf(GFP_KERNEL, "%s(%d:%s)", >> + cachep->name, css_id(&memcg->css), dentry->d_name.name); >> + >> + return name; >> +} > > Function allocates a string that is supposed to be disposed of by the > caller. That needs to be documented and maybe even the name needs to > reflect that. Okay, I can change it. >> --- a/mm/slub.c >> +++ b/mm/slub.c >> @@ -4002,6 +4002,38 @@ struct kmem_cache *kmem_cache_create(const char *name, size_t size, >> } >> EXPORT_SYMBOL(kmem_cache_create); >> >> +#ifdef CONFIG_CGROUP_MEM_RES_CTLR_KMEM >> +struct kmem_cache *kmem_cache_dup(struct mem_cgroup *memcg, >> + struct kmem_cache *s) >> +{ >> + char *name; >> + struct kmem_cache *new; >> + >> + name = mem_cgroup_cache_name(memcg, s); >> + if (!name) >> + return NULL; >> + >> + new = kmem_cache_create_memcg(memcg, name, s->objsize, s->align, >> + (s->allocflags& ~SLAB_PANIC), s->ctor); > > Hmmm... A full duplicate of the slab cache? We may have many sparsely > used portions of the per node and per cpu structure as a result. I've already commented on patch 0, but I will repeat it here. This approach leads to more fragmentation, yes, but this is exactly to be less intrusive. With a full copy, all I need to do is: 1) relay the allocation to the right cache. 2) account for a new page when it is needed. How does the cache work from inside? I don't care. Accounting pages seems just crazy to me. If new allocators come in the future, organizing the pages in a different way, instead of patching it here and there, we need to totally rewrite this. If those allocators happen to depend on a specific placement for performance, then we're destroying this as well too. > >> + * prevent it from being deleted. If kmem_cache_destroy() is >> + * called for the root cache before we call it for a child cache, >> + * it will be queued for destruction when we finally drop the >> + * reference on the child cache. >> + */ >> + if (new) { >> + down_write(&slub_lock); >> + s->refcount++; >> + up_write(&slub_lock); >> + } > > Why do you need to increase the refcount? You made a full copy right? Yes, but I don't want this copy to go away while we have other caches around. So, in the memcg internals, I used a different reference counter, to avoid messing with this one. I could use that, and leave the original refcnt alone. Would you prefer this? -- 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/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org