Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755052Ab2HXF1n (ORCPT ); Fri, 24 Aug 2012 01:27:43 -0400 Received: from mx2.parallels.com ([64.131.90.16]:44689 "EHLO mx2.parallels.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751275Ab2HXF1k (ORCPT ); Fri, 24 Aug 2012 01:27:40 -0400 Message-ID: <50370FEE.40106@parallels.com> Date: Fri, 24 Aug 2012 09:23:58 +0400 From: Glauber Costa User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:14.0) Gecko/20120717 Thunderbird/14.0 MIME-Version: 1.0 To: Greg Thelen CC: Michal Hocko , , , , , "Johannes Weiner" , Andrew Morton , , Christoph Lameter , "David Rientjes" , Pekka Enberg , "Pekka Enberg" , Suleiman Souhlal Subject: Re: [PATCH v2 09/11] memcg: propagate kmem limiting information to children References: <1344517279-30646-1-git-send-email-glommer@parallels.com> <1344517279-30646-10-git-send-email-glommer@parallels.com> <20120817090005.GC18600@dhcp22.suse.cz> <502E0BC3.8090204@parallels.com> <20120817093504.GE18600@dhcp22.suse.cz> <502E17C4.7060204@parallels.com> <20120817103550.GF18600@dhcp22.suse.cz> <502E1E90.1080805@parallels.com> <20120821075430.GA19797@dhcp22.suse.cz> <50335341.6010400@parallels.com> <20120821100007.GE19797@dhcp22.suse.cz> <503496D9.3020806@parallels.com> <5035E1D6.6010503@parallels.com> In-Reply-To: Content-Type: text/plain; charset="ISO-8859-1" Content-Transfer-Encoding: 7bit X-Originating-IP: [83.149.8.247] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3804 Lines: 83 On 08/24/2012 09:06 AM, Greg Thelen wrote: > On Thu, Aug 23 2012, Glauber Costa wrote: > >> On 08/23/2012 03:23 AM, Greg Thelen wrote: >>> On Wed, Aug 22 2012, Glauber Costa wrote: >>> >>>>>>> >>>>>>> I am fine with either, I just need a clear sign from you guys so I don't >>>>>>> keep deimplementing and reimplementing this forever. >>>>>> >>>>>> I would be for make it simple now and go with additional features later >>>>>> when there is a demand for them. Maybe we will have runtimg switch for >>>>>> user memory accounting as well one day. >>>>>> >>>>>> But let's see what others think? >>>>> >>>>> In my use case memcg will either be disable or (enabled and kmem >>>>> limiting enabled). >>>>> >>>>> I'm not sure I follow the discussion about history. Are we saying that >>>>> once a kmem limit is set then kmem will be accounted/charged to memcg. >>>>> Is this discussion about the static branches/etc that are autotuned the >>>>> first time is enabled? >>>> >>>> No, the question is about when you unlimit a former kmem-limited memcg. >>>> >>>>> The first time its set there parts of the system >>>>> will be adjusted in such a way that may impose a performance overhead >>>>> (static branches, etc). Thereafter the performance cannot be regained >>>>> without a reboot. This makes sense to me. Are we saying that >>>>> kmem.limit_in_bytes will have three states? >>>> >>>> It is not about performance, about interface. >>>> >>>> Michal says that once a particular memcg was kmem-limited, it will keep >>>> accounting pages, even if you make it unlimited. The limits won't be >>>> enforced, for sure - there is no limit, but pages will still be accounted. >>>> >>>> This simplifies the code galore, but I worry about the interface: A >>>> person looking at the current status of the files only, without >>>> knowledge of past history, can't tell if allocations will be tracked or not. >>> >>> In the current patch set we've conflating enabling kmem accounting with >>> the kmem limit value (RESOURCE_MAX=disabled, all_other_values=enabled). >>> >>> I see no problem with simpling the kernel code with the requirement that >>> once a particular memcg enables kmem accounting that it cannot be >>> disabled for that memcg. >>> >>> The only question is the user space interface. Two options spring to >>> mind: >>> a) Close to current code. Once kmem.limit_in_bytes is set to >>> non-RESOURCE_MAX, then kmem accounting is enabled and cannot be >>> disabled. Therefore the limit cannot be set to RESOURCE_MAX >>> thereafter. The largest value would be something like >>> RESOURCE_MAX-PAGE_SIZE. An admin wondering if kmem is enabled only >>> has to cat kmem.limit_in_bytes - if it's less than RESOURCE_MAX, then >>> kmem is enabled. >>> >> >> If we need to choose between them, I like this better than your (b). >> At least it is all clear, and "fix" the history problem, since it is >> possible to look up the status of the files and figure it out. >> >>> b) Or, if we could introduce a separate sticky kmem.enabled file. Once >>> set it could not be unset. Kmem accounting would only be enabled if >>> kmem.enabled=1. >>> >>> I think (b) is clearer. >>> >> Depends on your definition of clearer. We had a knob for >> kmem_independent in the beginning if you remember, and it was removed. >> The main reason being knobs complicate minds, and we happen to have a >> very natural signal for this. I believe the same reasoning applies here. > > Sounds good to me, so let's go with (a). > Michal, what do you think ? -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/