From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 4C99FC282C8 for ; Mon, 28 Jan 2019 14:28:24 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 1E05421741 for ; Mon, 28 Jan 2019 14:28:24 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1548685704; bh=hWp7o3RVVl3ZK/vSWf3bJ9nYc44PenZ1McFBVduAoa8=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=lb7Ra0rU0l2H8Gm8lzsCUGc2Rj5HqkFUoXokSBlR3uuwz6lfUMJSXxw1QEufM6wun g6CgVY/sdpx9//42caFcq7jz5lLw4zZ0LKQkX93FlHz61p9ParLNbMSyjWz9i4QGG7 iXstRho6V3o3szOWVGPoe8zdR4uQxnpFDnfHOHw0= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726818AbfA1O2W (ORCPT ); Mon, 28 Jan 2019 09:28:22 -0500 Received: from mail-yb1-f194.google.com ([209.85.219.194]:36628 "EHLO mail-yb1-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726266AbfA1O2W (ORCPT ); Mon, 28 Jan 2019 09:28:22 -0500 Received: by mail-yb1-f194.google.com with SMTP id 64so2231774ybf.3; Mon, 28 Jan 2019 06:28:21 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=sender:date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=16iA2KhpGFaktyfkAkUeDivlPZNfQCdHzHmJAlMfvm0=; b=OH9BmxAMpI2dn5E0OCOkDxyBFiuKIzG84TuAPLbsaHFD8Y4tP9t6UOgwYDLk0SqVJ+ rzNq4skU4+AoEyiSlUqHzLlGst9c7xkw0Y0CmKGKRy/PDltLoNyyp6NP9H7DbLDIgLLl ooA2hHi2wDoPsq5RGy9/kHshGlGlPbFv7UC+4PgqPmcimos7sshWy5k7tzbolHoIbGWA OkirYa+jyvJNqEbA1TyZ0BdTZxyM0Tb4H0zH+RE6jiXiAOfiCAEfggYon3kBS4Rqm9gk uh7Ofnetke+CLAiD+Pi3juRT6eSFijXtCTiFKPwl2pFbgKwasbvGf2jX0YSyCZ7kXQ2Q YI5w== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:sender:date:from:to:cc:subject:message-id :references:mime-version:content-disposition:in-reply-to:user-agent; bh=16iA2KhpGFaktyfkAkUeDivlPZNfQCdHzHmJAlMfvm0=; b=Cqvh7QjO1LDm9u+zDvRQOF20efVsl9j3CiV/GPWYkiZfN8HwgZzuiV/U1oEsHlmzYC yVcc7oNgIx6DOLO2Z+0mjhHsee4Vx7qI8B6woszQWbvUXkSTHuFl34ontZOz+6yPlVOG jCLuga/hQxZ/fGIhEuxaxhuqH/MwknfGH7mKQ/0UnQzHGmLXpLN1A3FahOo2XDzBhChl jMkvUnUR9ocwydjchHnxEyeHLxO8rUk0l79FgBwBhb7ei222ARwVJzQF7YIQ6q72VRiK Lgw927yNXLM1iPHve7RSVM/P62elUoQVaYRb6KWXuTd7MRSh9xdW9R1cVSX7Dhdp0J9Z vBRQ== X-Gm-Message-State: AJcUukdXguS8PYmatWYFduUmdJk0UBKt7g0WxnD3uiO90OLikRcuD7lc lXUa0UOBNze3klduZX3a5Aw= X-Google-Smtp-Source: ALg8bN6b97yjXesS3JpAR8TAdlO5u95HsT4J9nFbMu1NOwpOEfvBCc0iVD42Xa1Q948agPUfNW8g4g== X-Received: by 2002:a25:2447:: with SMTP id k68mr11281571ybk.249.1548685700851; Mon, 28 Jan 2019 06:28:20 -0800 (PST) Received: from localhost ([2620:10d:c091:200::7:a62a]) by smtp.gmail.com with ESMTPSA id o124sm11998848ywe.75.2019.01.28.06.28.19 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 28 Jan 2019 06:28:19 -0800 (PST) Date: Mon, 28 Jan 2019 06:28:16 -0800 From: Tejun Heo To: Michal Hocko Cc: Johannes Weiner , Chris Down , Andrew Morton , Roman Gushchin , Dennis Zhou , linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, linux-mm@kvack.org, kernel-team@fb.com Subject: Re: [PATCH 2/2] mm: Consider subtrees in memory.events Message-ID: <20190128142816.GM50184@devbig004.ftw2.facebook.com> References: <20190123223144.GA10798@chrisdown.name> <20190124082252.GD4087@dhcp22.suse.cz> <20190124160009.GA12436@cmpxchg.org> <20190124170117.GS4087@dhcp22.suse.cz> <20190124182328.GA10820@cmpxchg.org> <20190125074824.GD3560@dhcp22.suse.cz> <20190125165152.GK50184@devbig004.ftw2.facebook.com> <20190125173713.GD20411@dhcp22.suse.cz> <20190125182808.GL50184@devbig004.ftw2.facebook.com> <20190128125151.GI18811@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190128125151.GI18811@dhcp22.suse.cz> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hello, Michal. On Mon, Jan 28, 2019 at 01:51:51PM +0100, Michal Hocko wrote: > > For example, a workload manager watching over a subtree for a job with > > nested memory limits set by the job itself. It wants to take action > > (reporting and possibly other remediative actions) when something goes > > wrong in the delegated subtree but isn't involved in how the subtree > > is configured inside. > > Yes, I understand this part, but it is not clear to me, _how_ to report > anything sensible without knowing _what_ has caused the event. You can > walk the cgroup hierarchy and compare cached results with new ones but > this is a) racy and b) clumsy. All .events files generate aggregated stateful notifications. For anyone to do anything, they'd have to remember the previous state to identify what actually happened. Being hierarchical, it'd of course need to walk down when an event triggers. > > That sure is an option for use cases like above but it has the > > downside of carrying over the confusing interface into the indefinite > > future. > > I actually believe that this is not such a big deal. For one thing the > current events are actually helpful to watch the reclaim/setup behavior. Sure, it isn't something critical. It's just confusing and I think it'd be better to improve. > I do not really think you can go back. You cannot simply change semantic > back and forth because you just break new users. > > Really, I do not see the semantic changing after more than 3 years of > production ready interface. If you really believe we need a hierarchical > notification mechanism for the reclaim activity then add a new one. I don't see it as black and white as you do. Let's agree to disagree. I'll ack the patch and note the disagreement. Thanks. -- tejun