From mboxrd@z Thu Jan 1 00:00:00 1970 From: Glauber Costa Subject: Re: [PATCH v5 2/2] decrement static keys on real destroy time Date: Wed, 16 May 2012 10:03:08 +0400 Message-ID: <4FB3431C.3050402@parallels.com> References: <1336767077-25351-1-git-send-email-glommer@parallels.com> <1336767077-25351-3-git-send-email-glommer@parallels.com> <4FB058D8.6060707@jp.fujitsu.com> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <4FB058D8.6060707-+CUm20s59erQFUHtdCDX3A@public.gmane.org> Sender: cgroups-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-ID: Content-Type: text/plain; charset="us-ascii" To: KAMEZAWA Hiroyuki Cc: cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org, devel-GEFAQzZX7r8dnm+yROfE0A@public.gmane.org, netdev-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Tejun Heo , Li Zefan , Johannes Weiner , Michal Hocko On 05/14/2012 04:59 AM, KAMEZAWA Hiroyuki wrote: > (2012/05/12 5:11), Glauber Costa wrote: > >> We call the destroy function when a cgroup starts to be removed, >> such as by a rmdir event. >> >> However, because of our reference counters, some objects are still >> inflight. Right now, we are decrementing the static_keys at destroy() >> time, meaning that if we get rid of the last static_key reference, >> some objects will still have charges, but the code to properly >> uncharge them won't be run. >> >> This becomes a problem specially if it is ever enabled again, because >> now new charges will be added to the staled charges making keeping >> it pretty much impossible. >> >> We just need to be careful with the static branch activation: >> since there is no particular preferred order of their activation, >> we need to make sure that we only start using it after all >> call sites are active. This is achieved by having a per-memcg >> flag that is only updated after static_key_slow_inc() returns. >> At this time, we are sure all sites are active. >> >> This is made per-memcg, not global, for a reason: >> it also has the effect of making socket accounting more >> consistent. The first memcg to be limited will trigger static_key() >> activation, therefore, accounting. But all the others will then be >> accounted no matter what. After this patch, only limited memcgs >> will have its sockets accounted. >> >> [v2: changed a tcp limited flag for a generic proto limited flag ] >> [v3: update the current active flag only after the static_key update ] >> [v4: disarm_static_keys() inside free_work ] >> [v5: got rid of tcp_limit_mutex, now in the static_key interface ] >> >> Signed-off-by: Glauber Costa >> CC: Tejun Heo >> CC: Li Zefan >> CC: Kamezawa Hiroyuki >> CC: Johannes Weiner >> CC: Michal Hocko > > > Thank you for your patient works. > > Acked-by: KAMEZAWA Hiroyuki > > BTW, what is the relationship between 1/2 and 2/2 ? Can't do jump label patching inside an interrupt handler. They need to happen when we free the structure, and I was about to add a worker myself when I found out we already have one: just we don't always use it. Before we merge it, let me just make sure the issue with config Li pointed out don't exist. I did test it, but since I've reposted this many times with multiple tiny changes - the type that will usually get us killed, I'd be more comfortable with an extra round of testing if someone spotted a possibility. Who is merging this fix, btw ? I find it to be entirely memcg related, even though it touches a file in net (but a file with only memcg code in it)