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(p200300cbc707980059ba10069052fb40.dip0.t-ipconnect.de. [2003:cb:c707:9800:59ba:1006:9052:fb40]) by smtp.gmail.com with ESMTPSA id q3-20020adff503000000b002ca864b807csm22936582wro.0.2023.06.16.00.44.51 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 16 Jun 2023 00:44:52 -0700 (PDT) Message-ID: <29c9b998-f453-59f2-5084-9b4482b489cf@redhat.com> Date: Fri, 16 Jun 2023 09:44:50 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.12.0 To: Vishal Verma , "Rafael J. Wysocki" , Len Brown , Andrew Morton , Oscar Salvador , Dan Williams , Dave Jiang Cc: linux-acpi@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, nvdimm@lists.linux.dev, linux-cxl@vger.kernel.org, Huang Ying , Dave Hansen References: <20230613-vv-kmem_memmap-v1-0-f6de9c6af2c6@intel.com> From: David Hildenbrand Organization: Red Hat Subject: Re: [PATCH 0/3] mm: use memmap_on_memory semantics for dax/kmem In-Reply-To: <20230613-vv-kmem_memmap-v1-0-f6de9c6af2c6@intel.com> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 6FBD9100005 X-Rspam-User: X-Rspamd-Server: rspam11 X-Stat-Signature: 71pw7grotezuku1qrsrbzd1dc5jrpd1w X-HE-Tag: 1686901496-144540 X-HE-Meta: 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 p69RU6P2 lPdYK6MtihM1XKJw0y+ya+9hocH7STOxwxB9qcDL9cBMonPhbDesILrlWPSrEH/7P4UNAxzoIWg04tfI9v3TVyZztQfhoI9sEQjof/W5PxIV+Jg/bJgRvaP+f/cnd3Ip+0pLnXxqvCwYtoA42e7QEW03LrajbQyqfqCpQFOy922wjH0zPQgCgjES7IWWy9KJmPfMWRxkUBaPJmzAB2LasOs+h03jrcAz0pE272yS1iM3OI1bREeq9l96xdBjTx5ooxkjuUzcQjnpSVJyCOUH2aY6GPqJZrneQzk/UqD7Wtbk3FOtl/VvoLZ30alIIjVpYgGHtedCNdzI1cLIeORQvI/FRZo7mBLNOQveLEQ/i/vfcazvlMRg6I4MuzT+3njfJSZZNzXxch4jTh+fyiGJ7bHLGM6N3LxOu+WhUICRli5hXkC8= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 16.06.23 00:00, Vishal Verma wrote: > The dax/kmem driver can potentially hot-add large amounts of memory > originating from CXL memory expanders, or NVDIMMs, or other 'device > memories'. There is a chance there isn't enough regular system memory > available to fit ythe memmap for this new memory. It's therefore > desirable, if all other conditions are met, for the kmem managed memory > to place its memmap on the newly added memory itself. > > Arrange for this by first allowing for a module parameter override for > the mhp_supports_memmap_on_memory() test using a flag, adjusting the > only other caller of this interface in dirvers/acpi/acpi_memoryhotplug.c, > exporting the symbol so it can be called by kmem.c, and finally changing > the kmem driver to add_memory() in chunks of memory_block_size_bytes(). 1) Why is the override a requirement here? Just let the admin configure it then then add conditional support for kmem. 2) I recall that there are cases where we don't want the memmap to land on slow memory (which online_movable would achieve). Just imagine the slow PMEM case. So this might need another configuration knob on the kmem side. I recall some discussions on doing that chunk handling internally (so kmem can just perform one add_memory() and we'd split that up internally). -- Cheers, David / dhildenb