Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756684Ab2HXFG5 (ORCPT ); Fri, 24 Aug 2012 01:06:57 -0400 Received: from mail-wg0-f74.google.com ([74.125.82.74]:46529 "EHLO mail-wg0-f74.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750761Ab2HXFGy (ORCPT ); Fri, 24 Aug 2012 01:06:54 -0400 From: Greg Thelen To: Glauber Costa 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> Date: Thu, 23 Aug 2012 22:06:50 -0700 In-Reply-To: <5035E1D6.6010503@parallels.com> (Glauber Costa's message of "Thu, 23 Aug 2012 11:55:02 +0400") Message-ID: User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/23.3 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3658 Lines: 80 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). -- 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/