From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 02EAC3AD501; Mon, 15 Jun 2026 18:57:07 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781549827; cv=none; b=IlaU86FBykpsj56cYxv0oPPt2lM/WfPQ3OW72hfgnvHeP8xe/GYesq9PnZD/Ow1w9TsRQzCef1sr9mW2C5LmJVsywC1jvWS0R4N99PjvRwrF9Zl/RCLYVeGjgb9N3z7GHDf/h/u5+5NIzgfJgTeR0kqFf8MMb3rkvMkRYOUCoTs= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781549827; c=relaxed/simple; bh=ipTuWyEiQXg4CrHmekr0xKl3BUxx+ViO4QyjdDZgBOs=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=EUsbFgWnVh3B0vda0zqYklAZmUdd1QO2wKLOtz+wA0XzL4RRJnz/YdFauLU65FXFl4fZNrjH+h4LSuk6x99jpPXmAegZSHnMxfoXlL5YoMguQs37LsS9+ZZoumXWX1Y/YpDXZYa7mIPeBM3IV2bKZ6biPH6lrOnX+QmXOUXbfJI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=i+44SHLS; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="i+44SHLS" Received: by smtp.kernel.org (Postfix) with ESMTPSA id B149D1F000E9; Mon, 15 Jun 2026 18:57:06 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1781549826; bh=ZkxUGDLSZMr0Dq+DdzIPtXTXVSaYiY2WHl9OHQk/HmE=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=i+44SHLSEjFboHQKldJvgVHf3fFqesutTGQKBKUoBaYf1PDwTRUkh2KCBbfiv/zxK AHpovUOYmMej8NestBeihJK5CrLS5z7Hbvwf2Of7QJjOK4OxZokXnmRA73OfXZFZAn zdKEoHoe6a87h8z8m5TuXlcVyhmvLeMTAqSWmn5NjhSpJnBXUR32tU15ovJ5Bj/OXc 8g1oze2ON0nj84ddT6EiR8PjTYFECnDbTWQA60ql8B4kdR38mVdBh5ej7Kfj+/6GO8 iVlzkdwBGzWKAGCJ4MeDNp2MKoqtAIWvXoY3pt6YTKAE3kd6Qlra7H+r4/Tu+eEHVg yjEBRjBz88cPQ== Date: Mon, 15 Jun 2026 08:57:06 -1000 From: Tejun Heo To: Thomas =?iso-8859-1?Q?Hellstr=F6m?= Cc: intel-xe@lists.freedesktop.org, Natalie Vock , Johannes Weiner , Michal =?iso-8859-1?Q?Koutn=FD?= , cgroups@vger.kernel.org, Huang Rui , Matthew Brost , Matthew Auld , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , Simona Vetter , David Airlie , Christian =?iso-8859-1?Q?K=F6nig?= , Alex Deucher , Rodrigo Vivi , dri-devel@lists.freedesktop.org, amd-gfx@lists.freedesktop.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v6 0/6] [PATCH v6 0/6] Add reclaim to the dmem cgroup controller Message-ID: References: <20260611173301.17473-1-thomas.hellstrom@linux.intel.com> Precedence: bulk X-Mailing-List: cgroups@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Mon, Jun 15, 2026 at 08:49:55AM -1000, Tejun Heo wrote: > The canonical behavior for cgroup2 would be not failing the write at all > even when the usage can't be brought down below the new max. Updating the > target configuration and tracking the current usage are separate operations. > The former should just set max and trigger reclaim and a writer should not > assume that a successful write indicates that the usage is below the written > max value. Sent too early. One of the reasons is that cgroup is hierarchical and there can be multiple delegation layers and if you tie application of configuration to immediate enforcement, some hierarchical control actions become racy and awkward. Here's an example: Imagine a system agent trying to lower usage in a subtree which contains multiple delegated containers. If max can be set below what reclaim can achieve immediately, it can just set the max and if the usage is still too high, can go around and e.g. kill some of the containers. If max write fails, it'd have to kill and then try again and inbetween someone else might push up the usage. Thanks. -- tejun