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[2003:cb:c73f:e900:3b0d:87a6:2953:20d1]) by smtp.gmail.com with ESMTPSA id x17-20020adfffd1000000b003141f3843e6sm16751602wrs.90.2023.07.25.08.54.18 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 25 Jul 2023 08:54:19 -0700 (PDT) Message-ID: <1c3f737e-f5c6-b974-3b36-c4a3ada14422@redhat.com> Date: Tue, 25 Jul 2023 17:54:17 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.13.0 Subject: Re: [PATCH v2 0/3] mm: use memmap_on_memory semantics for dax/kmem To: Vishal Verma , Andrew Morton , Oscar Salvador , Dan Williams , Dave Jiang Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, nvdimm@lists.linux.dev, linux-cxl@vger.kernel.org, Huang Ying , Dave Hansen , "Aneesh Kumar K.V" , Jonathan Cameron , Jeff Moyer References: <20230720-vv-kmem_memmap-v2-0-88bdaab34993@intel.com> From: David Hildenbrand Organization: Red Hat In-Reply-To: <20230720-vv-kmem_memmap-v2-0-88bdaab34993@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-Stat-Signature: yasm6fk1uarkzo4wwitbs3d88bc1fudy X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 588291A000E X-Rspam-User: X-HE-Tag: 1690300463-505399 X-HE-Meta: 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 LR+scYYV 4LUAOPd6W4+QKIfROzyQlT35uEQlaLO8oXg0McaVKPFePJ7sGUcIkxuYhWL1fhdX85qOI4Uev1byYbOtWUEWyvOgPRjOMGi4PPrjq1NYSjE8LUSSqy//sXChc6Xsyf2NwdkbqCoUHcQknguZlNHwWHaLGSivr7TkAOWHN7nid6oLWsQNNxU5v5u34wnxcnUx4g2JQDNL/YN+g1GDjwITMohSyK2yqPGACzzi2gNdnqNB0I0LBc/RGRy9xShCBc0Bdxv/ZdL0giPQDmDXI1FB8LWdLnzocUb5iIhcW1n9lGd+FPpcfKI0rHqavkYHGabgoq7v4zkBZhLCw9vnQ3HT1Mqd19c8v33Y4bLeeqyC/ZY70GckrjiqEqUOEUuCgQ0L5/50tTi1FgPkL+Sw7AgLX4c2kpXUhBIPftpneUcHkZAEQ2NkRd6SwLiurSg== 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 20.07.23 09:14, 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 the 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. > > The main hurdle for accomplishing this for kmem is that memmap_on_memory > can only be done if the memory being added is equal to the size of one > memblock. To overcome this,allow the hotplug code to split an add_memory() > request into memblock-sized chunks, and try_remove_memory() to also > expect and handle such a scenario. > > Patch 1 exports mhp_supports_memmap_on_memory() so it can be used by the > kmem driver. > > Patch 2 teaches the memory_hotplug code to allow for splitting > add_memory() and remove_memory() requests over memblock sized chunks. > > Patch 3 adds a sysfs control for the kmem driver that would > allow an opt-out of using memmap_on_memory for the memory being added. > It might be reasonable to rebase this on Aneesh's work. For example, patch #1 might not be required anymore. -- Cheers, David / dhildenb