From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from lankhorst.se (unknown [141.105.120.124]) (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 1D28C494A1B for ; Tue, 4 Aug 2026 20:23:13 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=141.105.120.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785875011; cv=none; b=PKkWGKvA3ftswN7MD7hP1HBxkY5fz++Atrswgj1sbn1L9NOV0AbowoZesjnllro4yesVF2GTxhGzWR7yZ768amIZ21t7PT6wdu8wUIT+RHZXsk19DFEt1odQDjQKGd0i+TIMLDW609s1rW5QonGD/b62BQ6mC66HVzgJ9Z/HAqw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785875011; c=relaxed/simple; bh=dHRRYCr6KNXPQ/XC3VIjH4wQn3v7mHs7limZc8dV07w=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=tktoPVWAqUfKlX2+lRu9qemqPsLVnBStiFtMI2T7qN8RKWumB+z0ArseT0+iDUyWqEO+zqQAPrJeIxd6oNg+MafEbjfFvEKleti87zE3mEV9h9p32RlDFnwBz8x2SDWgaIWBkAUYlL+IwENXUQ3ucsmyQ5Np8VV19KeRUaEpQhQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=lankhorst.se; spf=pass smtp.mailfrom=lankhorst.se; dkim=pass (2048-bit key) header.d=lankhorst.se header.i=@lankhorst.se header.b=RgrMpsLG; arc=none smtp.client-ip=141.105.120.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=lankhorst.se Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=lankhorst.se Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=lankhorst.se header.i=@lankhorst.se header.b="RgrMpsLG" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=lankhorst.se; s=default; t=1785874639; bh=dHRRYCr6KNXPQ/XC3VIjH4wQn3v7mHs7limZc8dV07w=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=RgrMpsLGhMHrvhXETcOnUlgTp2Cku8y6q4XDrRMwzak0C7NG5WtLfiwa4IP9tC8J1 y0WXbpfIinT8aEKyLCq1cHgwCJFT47cCER/oHQ8TZSXZDac4zTnxUj/Mdg4FFnSTbp gGq3HLv1fNAkXTCJGHAEnB7ZqYohflhSfx5s/GtwSWib0cOvYWB8qqnegGwX9KuYmF JZphUsZ6RM3SPT0WeLBEJwzbIaEtGhIcmJNzUaT1XWGl8uvGDukDTsfu6WQTI/M8un YCc1eaQ0saK7h/coYFZLi+9jrgneOYye7RqpkMGOf1oXeGfZgg7OqO5VRAv3x3Bu6X RSYenpeRdV98Q== Message-ID: Date: Tue, 4 Aug 2026 22:18:32 +0200 Precedence: bulk X-Mailing-List: cgroups@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v8 2/6] cgroup,cgroup/dmem: Add (dmem_)cgroup_common_ancestor helper To: Natalie Vock , Maxime Ripard , Tejun Heo , Johannes Weiner , =?UTF-8?Q?Michal_Koutn=C3=BD?= , Christian Koenig , Huang Rui , Matthew Auld , Matthew Brost , Maarten Lankhorst , Thomas Zimmermann , David Airlie , Simona Vetter , Tvrtko Ursulin , Thadeu Lima de Souza Cascardo , =?UTF-8?Q?Timur_Krist=C3=B3f?= Cc: cgroups@vger.kernel.org, dri-devel@lists.freedesktop.org References: <20260804-dmemcg-aggressive-protect-v8-0-07af96681bf8@gmx.de> <20260804-dmemcg-aggressive-protect-v8-2-07af96681bf8@gmx.de> Content-Language: en-US From: Maarten Lankhorst In-Reply-To: <20260804-dmemcg-aggressive-protect-v8-2-07af96681bf8@gmx.de> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 8/4/26 10:25, Natalie Vock wrote: > This helps to find a common subtree of two resources, which is important > when determining whether it's helpful to evict one resource in favor of > another. > > To facilitate this, add a common helper to find the ancestor of two > cgroups using each cgroup's ancestor array. > > Signed-off-by: Natalie Vock > --- > include/linux/cgroup.h | 21 +++++++++++++++++++++ > include/linux/cgroup_dmem.h | 9 +++++++++ > kernel/cgroup/dmem.c | 41 +++++++++++++++++++++++++++++++++++++++++ > 3 files changed, 71 insertions(+) > > diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h > index f2aa46a4f871e..83a17ded1c516 100644 > --- a/include/linux/cgroup.h > +++ b/include/linux/cgroup.h > @@ -623,6 +623,27 @@ static inline struct cgroup *cgroup_ancestor(struct cgroup *cgrp, > return cgrp->ancestors[ancestor_level]; > } > > +/** > + * cgroup_common_ancestor - find common ancestor of two cgroups > + * @a: first cgroup to find common ancestor of > + * @b: second cgroup to find common ancestor of > + * > + * Find the first cgroup that is an ancestor of both @a and @b, if it exists > + * and return a pointer to it. If such a cgroup doesn't exist, return NULL. > + * > + * This function is safe to call as long as both @a and @b are accessible. > + */ > +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; > +} > + > /** > * task_under_cgroup_hierarchy - test task's membership of cgroup ancestry > * @task: the task to be tested > diff --git a/include/linux/cgroup_dmem.h b/include/linux/cgroup_dmem.h > index 1a88cd0c9eb00..9d72457c4cb9d 100644 > --- a/include/linux/cgroup_dmem.h > +++ b/include/linux/cgroup_dmem.h > @@ -28,6 +28,8 @@ bool dmem_cgroup_below_min(struct dmem_cgroup_pool_state *root, > struct dmem_cgroup_pool_state *test); > bool dmem_cgroup_below_low(struct dmem_cgroup_pool_state *root, > struct dmem_cgroup_pool_state *test); > +struct dmem_cgroup_pool_state *dmem_cgroup_get_common_ancestor(struct dmem_cgroup_pool_state *a, > + struct dmem_cgroup_pool_state *b); > > void dmem_cgroup_pool_state_put(struct dmem_cgroup_pool_state *pool); > #else > @@ -75,6 +77,13 @@ static inline bool dmem_cgroup_below_low(struct dmem_cgroup_pool_state *root, > return false; > } > > +static inline > +struct dmem_cgroup_pool_state *dmem_cgroup_get_common_ancestor(struct dmem_cgroup_pool_state *a, > + struct dmem_cgroup_pool_state *b) > +{ > + return NULL; > +} > + > static inline void dmem_cgroup_pool_state_put(struct dmem_cgroup_pool_state *pool) > { } > > diff --git a/kernel/cgroup/dmem.c b/kernel/cgroup/dmem.c > index 9df3b33c65046..a587611ca2235 100644 > --- a/kernel/cgroup/dmem.c > +++ b/kernel/cgroup/dmem.c > @@ -762,6 +762,47 @@ bool dmem_cgroup_below_low(struct dmem_cgroup_pool_state *root, > } > EXPORT_SYMBOL_GPL(dmem_cgroup_below_low); > > +/** > + * dmem_cgroup_get_common_ancestor(): Find the first common ancestor of two pools. > + * @a: First pool to find the common ancestor of. > + * @b: First pool to find the common ancestor of. > + * > + * Return: The first pool that is a parent of both @a and @b, or NULL if either @a or @b are NULL, > + * or if such a pool does not exist. A reference to the returned pool is grabbed and must be > + * released by the caller when it is done using the pool. > + */ > +struct dmem_cgroup_pool_state *dmem_cgroup_get_common_ancestor(struct dmem_cgroup_pool_state *a, > + struct dmem_cgroup_pool_state *b) > +{ > + struct cgroup *ancestor_cgroup; > + struct cgroup_subsys_state *ancestor_css; > + struct dmemcg_state *ancestor_dmemcs = NULL; > + struct dmem_cgroup_pool_state *pool = NULL; > + > + if (!a || !b) > + return NULL; > + > + ancestor_cgroup = cgroup_common_ancestor(a->cs->css.cgroup, b->cs->css.cgroup); > + if (!ancestor_cgroup) > + return NULL; > + > + rcu_read_lock(); > + ancestor_css = cgroup_e_css(ancestor_cgroup, &dmem_cgrp_subsys); > + if (css_tryget(ancestor_css)) > + ancestor_dmemcs = css_to_dmemcs(ancestor_css); > + rcu_read_unlock(); > + > + if (ancestor_dmemcs) { > + pool = get_cg_pool_unlocked(css_to_dmemcs(ancestor_css), > + a->region); > + if (IS_ERR(pool)) > + pool = NULL; This should probably be a warn_on as this can never happen, sashiko is wrong here. If a and b are charged, all their ancestors are charged too. And when they share a common ancestor, then the common ancestor has to have an existing charged pool as well because there's a huge bug in the code otherwise. > + css_put(ancestor_css); > + } > + return pool; > +} > +EXPORT_SYMBOL_GPL(dmem_cgroup_get_common_ancestor); > + > static int dmem_cgroup_region_capacity_show(struct seq_file *sf, void *v) > { > struct dmem_cgroup_region *region; > Otherwise looks good, so feel free to extend my r-b to this patch too, and with that minor fix up commit it. Reviewed-by: Maarten Lankhorst