Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754056Ab2HVXXT (ORCPT ); Wed, 22 Aug 2012 19:23:19 -0400 Received: from mail-we0-f202.google.com ([74.125.82.202]:38256 "EHLO mail-we0-f202.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752507Ab2HVXXQ (ORCPT ); Wed, 22 Aug 2012 19:23:16 -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> Date: Wed, 22 Aug 2012 16:23:12 -0700 In-Reply-To: <503496D9.3020806@parallels.com> (Glauber Costa's message of "Wed, 22 Aug 2012 12:22:49 +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: 2891 Lines: 65 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. 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. -- 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/