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[2003:cb:c740:5d00:5143:1cd2:a300:ceff]) by smtp.gmail.com with ESMTPSA id m15-20020a056000008f00b0031417b0d338sm10543620wrx.87.2023.08.07.05.41.32 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 07 Aug 2023 05:41:32 -0700 (PDT) Message-ID: Date: Mon, 7 Aug 2023 14:41:31 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.13.0 To: Michal Hocko , Aneesh Kumar K V References: <31305ab7-1e65-80aa-ee91-9190c8f67430@redhat.com> <1c6a74f0-85e9-5299-1520-9068e842b1a5@redhat.com> From: David Hildenbrand Organization: Red Hat Subject: Re: [PATCH v7 7/7] mm/memory_hotplug: Enable runtime update of memmap_on_memory parameter In-Reply-To: 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-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linux-mm@kvack.org, npiggin@gmail.com, Vishal Verma , akpm@linux-foundation.org, linuxppc-dev@lists.ozlabs.org, Oscar Salvador Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On 07.08.23 14:27, Michal Hocko wrote: > On Sat 05-08-23 19:54:23, Aneesh Kumar K V wrote: > [...] >> Do you see a need for firmware-managed memory to be hotplugged in with >> different memory block sizes? > > In short. Yes. Slightly longer, a fixed size memory block semantic is > just standing in the way and I would even argue it is actively harmful. > Just have a look at ridicously small memory blocks on ppc. I do > understand that it makes some sense to be aligned to the memory model > (so sparsmem section aligned). In an ideal world, memory hotplug v2 > interface (if we ever go that path) should be physical memory range based. Yes, we discussed that a couple of times already (and so far nobody cared to implement any of that). Small memory block sizes are very beneficial for use cases like PPC dlar, virtio-mem, hyperv-balloon, ... essentially in most virtual environments where you might want to add/remove memory in very small granularity. I don't see that changing any time soon. Rather the opposite. Small memory block sizes are suboptimal for large machines where you might never end up removing such memory (boot memory), or when dealing with devices that can only be removed in one piece (DIMM/kmem). We already have memory groups in place to model that. For the latter it might be beneficial to have memory blocks of larger size that correspond to the physical memory ranges. That might also make a memmap (re-)configuration easier. Not sure if that is standing in any way or is harmful, though. -- Cheers, David / dhildenb