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 Received: from gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 4DD1AFD3773 for ; Wed, 25 Feb 2026 17:16:04 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 9315E10E7C9; Wed, 25 Feb 2026 17:16:03 +0000 (UTC) Authentication-Results: gabe.freedesktop.org; dkim=pass (2048-bit key; unprotected) header.d=kernel.org header.i=@kernel.org header.b="emxViB2P"; dkim-atps=neutral Received: from sea.source.kernel.org (sea.source.kernel.org [172.234.252.31]) by gabe.freedesktop.org (Postfix) with ESMTPS id 5B41D10E7C9 for ; Wed, 25 Feb 2026 17:16:02 +0000 (UTC) Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by sea.source.kernel.org (Postfix) with ESMTP id 8F9DB43CDC; Wed, 25 Feb 2026 17:16:01 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 385F6C2BCB2; Wed, 25 Feb 2026 17:16:01 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1772039761; bh=jJdzvVKMl5cn0QuJzc7vXdV0mAMHYhsXz6osLCyQqkg=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=emxViB2PRoqwP7d4rpdwXv6bTCYQD9BI/qjOXLPFK0TrQPZzPJGxNADxmpSJnb37j YpsCB0CfrboereOvxHKjW58gmH5ODcAIpLzVpFXnau81eTf4/oEKThJrlILMhCa0NQ 5KXqx6V3m4mzhaaCgKvjZnIPAFc1A3MM+tPLkeDQnMwSAaNBHqxx2xckYmt8WUdztq troKRrGbl8HVYsfLjzzNWQM6mHPPTvcSLErcfeQQlE16h8IMb6l34FJyk6p6w5IycN mOp7VkzMrw8hL5bq4l92ZUNJ4TxTjkX2Ko4X1faJJ5API/6d1qrpQHFL2aI7+/KUJD q1tpj4XcO9Tug== Date: Wed, 25 Feb 2026 07:16:00 -1000 Message-ID: From: Tejun Heo To: Natalie Vock Cc: Maarten Lankhorst , Maxime Ripard , Johannes Weiner , Michal Koutny , Christian Koenig , Huang Rui , Matthew Auld , Matthew Brost , Maarten Lankhorst , Thomas Zimmermann , David Airlie , Simona Vetter , Tvrtko Ursulin , cgroups@vger.kernel.org, dri-devel@lists.freedesktop.org Subject: Re: [PATCH v4 2/6] cgroup/dmem: Add dmem_cgroup_common_ancestor helper In-Reply-To: <20260225-dmemcg-aggressive-protect-v4-2-de847ab35184@gmx.de> References: <20260225-dmemcg-aggressive-protect-v4-0-de847ab35184@gmx.de> <20260225-dmemcg-aggressive-protect-v4-2-de847ab35184@gmx.de> X-BeenThere: dri-devel@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Direct Rendering Infrastructure - Development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" Each cgroup already knows all its ancestors in cgrp->ancestors[] along with its depth in cgrp->level (see cgroup_is_descendant() and cgroup_ancestor()). This can be used to implement a generic cgroup_common_ancestor() a lot more efficiently. Something like: static inline struct cgroup *cgroup_common_ancestor(struct cgroup *a, struct cgroup *b) { int level; for (level = min(a->level, b->level); level >= 0; level--) if (a->ancestors[level] == b->ancestors[level]) return a->ancestors[level]; return NULL; } This is O(depth) instead of O(n*m). Can you add a helper like the above in include/linux/cgroup.h and use it here? Thanks. -- tejun