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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 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 X-Rspamd-Queue-Id: 707F420018 X-Stat-Signature: os3pw8ynb5u6b9ap5f6b5z3qyie7i1r6 X-Rspam-User: X-Rspamd-Server: rspam02 X-HE-Tag: 1776092805-31192 X-HE-Meta: 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 QFs2nbSU JfriVUBgRNHPGwAeQETO0HbKwT7bzvmD3/7BOW7J0pNYpq/YK0agiacPJ+mBOPXJxPdp4DlWYsNS7iXXEfm+g9Uub1qaXJS9jTTNv2qQvZzJ+bd3UDCqHiAuq4KJmEjftWrDqNHsjNq/5uTGO+QO4MQFix8Dj1CnKbF/nbm4mMPuk52/IC0SbUwBtjgpq/1ner0aIciBgE/M4/fV2h+siin/NQbIa6UJ28D1kzBtOXkuMN+iNJVunhT3N7MWuv3lTzrBIfTXHxwIBlrad1hpNfKcY74oCGCwlE38gF9ig1cxMkb+n50A6NRx8cg== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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