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[173.79.56.208]) by smtp.gmail.com with ESMTPSA id 6a1803df08f44-6e8f715b809sm73419286d6.79.2025.03.11.08.58.57 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 11 Mar 2025 08:58:58 -0700 (PDT) Date: Tue, 11 Mar 2025 11:58:56 -0400 From: Gregory Price To: Zi Yan Cc: David Hildenbrand , Yang Shi , lsf-pc@lists.linux-foundation.org, linux-mm@kvack.org, linux-cxl@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: CXL Boot to Bash - Section 3: Memory (block) Hotplug Message-ID: References: <1b4c6442-a2b0-4290-8b89-c7b82a66d358@redhat.com> <4ae838ee-b079-408e-8799-e9530ca50417@redhat.com> <0C5749C4-B3EE-4393-A8EA-AA56B399E9E3@nvidia.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <0C5749C4-B3EE-4393-A8EA-AA56B399E9E3@nvidia.com> X-Rspam-User: X-Rspamd-Queue-Id: 41D85180008 X-Rspamd-Server: rspam03 X-Stat-Signature: d7r9it9b4e4q4y5zwmfcwncc1m3hnu1u X-HE-Tag: 1741708739-111301 X-HE-Meta: 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 qqZNyWW/ FlszYDM8e+ZqtEU4n/DiGMfkxRWbPRmNDs9c8kKMTYhvrx8P0fPBckXqptgVbvZcalQf2rW3hQFsrg9ekGnYjaJGGMDvScWyWPLIvQ1ml7Sz41LjHBjq+OTplUyuo4ZWX36k3tckF8mg8eoC7n9//u2nFhfD9KnzB96rK4Z+jSKMZ1An6OHsTvG9raHkKG7qW3MOL492f2BVFirD+r/oAN9O2MeKUjE55Csi/T70lRh1M1vy9y+0JXOHg2+e6+lIZbPKZ0cj5qcvfB494b/H1IbD1EgyE9L7uzowe35IQ1YxVPyjopqhRUWD+vBec1XrHBvCeBHXCB1Iis+ZbJD/Ig4lWOij3GVM8udum X-Bogosity: Ham, tests=bogofilter, spamicity=0.003445, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, Mar 11, 2025 at 10:53:41AM -0400, Zi Yan wrote: > On 20 Feb 2025, at 14:26, David Hildenbrand wrote: > > > Yes, the only way to get some 1 GiB pages is by using larger memory blocks (e.g., 2 GiB on x86-64), which comes with a different set of issues (esp. hotplug granularity). > > An alternative I can think of is to mark a hot-plugged memory block dedicated > to memmap and use it for new memory block’s memmap provision. In this way, > a 256MB memory block can be used for 256MB*(256MB/4MB)=16GB hot plugged memory. > Yes, it will waste memory before 256MB+16GB is online, but that might be > easier to handle than variable sized memory block, I suppose? > > > The devil is in the details here. We'd need a way for the driver to tell hotplug "use this for memmap for some yet-to-be-mapped region" - rather than having that allocate naturally. Either this, or a special ZONE specifically for memmap allocations. ~Gregory