From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 74677303CAB; Mon, 13 Apr 2026 15:06:44 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776092804; cv=none; b=EOKbHXre7Xk4UXhlROmsUjjJPoppu3B/ck9oggJH6tOaibLszcH1DJ0PaIHPJQCuwYbA78KSI224W7OmOWNPPSxTFMqlqRyW6pvaLiQRG5UIz/QiAEeKPbmOniJ3fpUaD3808W17TfTaabuuxmWeR9qXj0znss8YiFb86wlhXk0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776092804; c=relaxed/simple; bh=TD6ShOQz4Nkn+ZNt66HT4jCoXRRW5WRA+BumLhrc8fM=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=T4AXyCg2n7Bt6wQ0Zc+nMtc0PTK5EJw6UkNW3f+a/esomkhf8eB1t3tK7FgMuM5vEZXz1HYBUF4P87Ryyz/pGC0VlC5Q+iCK8S2j8povjPdRX30G0q2D4jJ1995G31rht0t1EgDhEt3HQTvMyWcGZh1qpWEt9srYkaDhdUaPWs8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=ebbqxqc+; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="ebbqxqc+" Received: by smtp.kernel.org (Postfix) with ESMTPSA id AEB59C2BCAF; Mon, 13 Apr 2026 15:06:39 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1776092804; bh=TD6ShOQz4Nkn+ZNt66HT4jCoXRRW5WRA+BumLhrc8fM=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=ebbqxqc+R4FIvsVY6sm40MMaHyoodjWD7ZsSW6ZHQqtYugUNdo141vEnDcGjNugPf Sw5bl1dKACwqFkek6obR6tmWue/gxRiDQ341vVyINQ6PkH+7ARRJFhPHRo7NlERTtQ 6MRhcQ0lvpYCbgO3hlxSGT9rpGZ6EnQjftMhg0i07Heoz9g+OvfTohhOFMU8E1ZaRG OTjlgEqLz0GPEo9XxCDJ+IoAHbWPlO253CT0hn+1Rdg7rDWk26tnBGzOMt2/EBrAB5 DRLF+wISJ5zC+4Ar/jKZ22o9LiCBmUuWlr6s9fxYPcLkl2hG40/GpqyTx+ZXBg0peX HIhSalvQ8M4Rw== Message-ID: Date: Mon, 13 Apr 2026 17:06:35 +0200 Precedence: bulk X-Mailing-List: linux-cxl@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/8] mm/memory-tiers: consolidate memory type dedup into mt_get_memory_type() To: Gregory Price , linux-mm@kvack.org, vishal.l.verma@intel.com, dave.jiang@intel.com, akpm@linux-foundation.org, osalvador@suse.de Cc: dan.j.williams@intel.com, ljs@kernel.org, Liam.Howlett@oracle.com, vbabka@kernel.org, rppt@kernel.org, surenb@google.com, mhocko@suse.com, linux-kernel@vger.kernel.org, nvdimm@lists.linux.dev, linux-cxl@vger.kernel.org, kernel-team@meta.com References: <20260321150404.3288786-1-gourry@gourry.net> <20260321150404.3288786-2-gourry@gourry.net> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 3/21/26 16:03, Gregory Price wrote: > Replace per-driver memory type list infrastructure with a single > mt_get_memory_type(adist) that deduplicates against the global > default_memory_types list under memory_tier_lock. > > The per-driver lists (mutex + list_head + find/put wrappers) provided > dedup within a single driver, but not across drivers or with the core. > Since the number of distinct adist values is bounded and types on > default_memory_types are never freed anyway, the per-driver cleanup > on module unload was not useful. > > Add MEMTIER_DEFAULT_LOWTIER_ADISTANCE to replace the default DAX > adistance, since it was really used as a standin for all kmem hotplugged > memory. This at least makes the default tier relationship clearer to > other drivers and they can see where to put their memory in relation to > the default lower tier. Very confusing code. What's the purpose of kref_get/kref_put if "the types on default_memory_types are never freed anyway" ? IIUC, init_node_memory_type() is always called with one of the types obtained through mt_get_memory_type(). And that one always gives us one from the default_memory_types list, no? Why does mt_find_alloc_memory_type() now even consume a list, if there really only is &default_memory_types? Is there even a need to expose the "struct memory_dev_type" to kmem, when all it does is effectively passing a reference to init_node_memory_type() / clear_node_memory_type(). IOW, couldn't init_node_memory_type()/clear_node_memory_type() just consume the "adist", and lookup the memory type itself? All you'd need is some way in the driver to verify that there is a memory type for the given adist, as some kind of prepare step. Alternatively, let init_node_memory_type() return an error to get a clean interface? :) [...] > mapped++; > } > + data->mtype = mtype; > > dev_set_drvdata(dev, data); > > @@ -253,7 +233,7 @@ static void dev_dax_kmem_remove(struct dev_dax *dev_dax) > * for that. This implies this reference will be around > * till next reboot. > */ > - clear_node_memory_type(node, NULL); > + clear_node_memory_type(node, data->mtype); > } Likely clear_node_memory_type() can now be taught to not handle "!memtype" anymore? -- Cheers, David