From mboxrd@z Thu Jan 1 00:00:00 1970 From: Glauber Costa Subject: Re: [PATCH] memcg: fix memcg_cache_name() to use cgroup_name() Date: Fri, 22 Mar 2013 14:25:23 +0400 Message-ID: <514C3193.9010609@parallels.com> References: <20130321090849.GF6094@dhcp22.suse.cz> <20130321102257.GH6094@dhcp22.suse.cz> <514BB23E.70908@huawei.com> <20130322080749.GB31457@dhcp22.suse.cz> <514C1388.6090909@huawei.com> <514C14BF.3050009@parallels.com> <20130322093141.GE31457@dhcp22.suse.cz> <514C2754.4080701@parallels.com> <20130322094832.GG31457@dhcp22.suse.cz> <514C2C72.5090402@parallels.com> <20130322100609.GI31457@dhcp22.suse.cz> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20130322100609.GI31457-2MMpYkNvuYDjFM9bn6wA6Q@public.gmane.org> Sender: cgroups-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-ID: Content-Type: text/plain; charset="us-ascii" To: Michal Hocko Cc: Li Zefan , Tejun Heo , LKML , Cgroups , linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org, KAMEZAWA Hiroyuki , Johannes Weiner On 03/22/2013 02:06 PM, Michal Hocko wrote: > On Fri 22-03-13 14:03:30, Glauber Costa wrote: >> On 03/22/2013 01:48 PM, Michal Hocko wrote: >>> On Fri 22-03-13 13:41:40, Glauber Costa wrote: >>>> On 03/22/2013 01:31 PM, Michal Hocko wrote: >>>>> On Fri 22-03-13 12:22:23, Glauber Costa wrote: >>>>>> On 03/22/2013 12:17 PM, Li Zefan wrote: >>>>>>>> GFP_TEMPORARY groups short lived allocations but the mem cache is not >>>>>>>>> an ideal candidate of this type of allocations.. >>>>>>>>> >>>>>>> I'm not sure I'm following you... >>>>>>> >>>>>>> char *memcg_cache_name() >>>>>>> { >>>>>>> char *name = alloc(); >>>>>>> return name; >>>>>>> } >>>>>>> >>>>>>> kmem_cache_dup() >>>>>>> { >>>>>>> name = memcg_cache_name(); >>>>>>> kmem_cache_create_memcg(name); >>>>>>> free(name); >>>>>>> } >>>>>>> >>>>>>> Isn't this a short lived allocation? >>>>>>> >>>>>> >>>>>> Hi, >>>>>> >>>>>> Thanks for identifying and fixing this. >>>>>> >>>>>> Li is right. The cache name will live long, but this is because the >>>>>> slab/slub caches will strdup it internally. So the actual memcg >>>>>> allocation is short lived. >>>>> >>>>> OK, I have totally missed that. Sorry about the confusion. Then all the >>>>> churn around the allocation is pointless, no? >>>>> What about: >>>> >>>> If we're really not concerned about stack, then yes. Even if always >>>> running from workqueues, a PAGE_SIZEd stack variable seems risky to me. >>> >>> This is not on stack. It is static >>> >> Ah, right, I totally missed that. And then you're taking the mutex. >> >> But actually, you don't need to take the mutex. All calls to >> kmem_cache_dup are protected by the memcg_cache_mutex. > > Yes and I am not taking that mutex. I've just added lockdep assert to > make sure that this still holds true. > It is impressive what a busy week does to our brains... I read the code as lockdep_assert(memcg_cache_mutex), and then later on mutex_lock(&memcg_mutex). But reading again, that was a just an rcu_read_lock(). Good thing it is Friday You guys can add my Acked-by, and thanks again