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[80.187.83.110]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-4255d8acc4csm25683339f8f.16.2025.10.07.09.11.15 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 07 Oct 2025 09:11:17 -0700 (PDT) Message-ID: Date: Tue, 7 Oct 2025 18:11:14 +0200 Precedence: bulk X-Mailing-List: linux-s390@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 0/4] Support dynamic (de)configuration of memory To: Sumanth Korikkar , Andrew Morton , linux-mm Cc: LKML , linux-s390 , Gerald Schaefer , Heiko Carstens , Vasily Gorbik , Alexander Gordeev References: <20250926131527.3260733-1-sumanthk@linux.ibm.com> From: David Hildenbrand Content-Language: en-US Autocrypt: addr=david@redhat.com; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzSREYXZpZCBIaWxk ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwZoEEwEIAEQCGwMCF4ACGQEFCwkIBwICIgIG FQoJCAsCBBYCAwECHgcWIQQb2cqtc1xMOkYN/MpN3hD3AP+DWgUCaJzangUJJlgIpAAKCRBN 3hD3AP+DWhAxD/9wcL0A+2rtaAmutaKTfxhTP0b4AAp1r/eLxjrbfbCCmh4pqzBhmSX/4z11 opn2KqcOsueRF1t2ENLOWzQu3Roiny2HOU7DajqB4dm1BVMaXQya5ae2ghzlJN9SIoopTWlR 0Af3hPj5E2PYvQhlcqeoehKlBo9rROJv/rjmr2x0yOM8qeTroH/ZzNlCtJ56AsE6Tvl+r7cW 3x7/Jq5WvWeudKrhFh7/yQ7eRvHCjd9bBrZTlgAfiHmX9AnCCPRPpNGNedV9Yty2Jnxhfmbv Pw37LA/jef8zlCDyUh2KCU1xVEOWqg15o1RtTyGV1nXV2O/mfuQJud5vIgzBvHhypc3p6VZJ lEf8YmT+Ol5P7SfCs5/uGdWUYQEMqOlg6w9R4Pe8d+mk8KGvfE9/zTwGg0nRgKqlQXrWRERv cuEwQbridlPAoQHrFWtwpgYMXx2TaZ3sihcIPo9uU5eBs0rf4mOERY75SK+Ekayv2ucTfjxr Kf014py2aoRJHuvy85ee/zIyLmve5hngZTTe3Wg3TInT9UTFzTPhItam6dZ1xqdTGHZYGU0O otRHcwLGt470grdiob6PfVTXoHlBvkWRadMhSuG4RORCDpq89vu5QralFNIf3EysNohoFy2A LYg2/D53xbU/aa4DDzBb5b1Rkg/udO1gZocVQWrDh6I2K3+cCs7BTQRVy5+RARAA59fefSDR 9nMGCb9LbMX+TFAoIQo/wgP5XPyzLYakO+94GrgfZjfhdaxPXMsl2+o8jhp/hlIzG56taNdt VZtPp3ih1AgbR8rHgXw1xwOpuAd5lE1qNd54ndHuADO9a9A0vPimIes78Hi1/yy+ZEEvRkHk /kDa6F3AtTc1m4rbbOk2fiKzzsE9YXweFjQvl9p+AMw6qd/iC4lUk9g0+FQXNdRs+o4o6Qvy iOQJfGQ4UcBuOy1IrkJrd8qq5jet1fcM2j4QvsW8CLDWZS1L7kZ5gT5EycMKxUWb8LuRjxzZ 3QY1aQH2kkzn6acigU3HLtgFyV1gBNV44ehjgvJpRY2cC8VhanTx0dZ9mj1YKIky5N+C0f21 zvntBqcxV0+3p8MrxRRcgEtDZNav+xAoT3G0W4SahAaUTWXpsZoOecwtxi74CyneQNPTDjNg azHmvpdBVEfj7k3p4dmJp5i0U66Onmf6mMFpArvBRSMOKU9DlAzMi4IvhiNWjKVaIE2Se9BY FdKVAJaZq85P2y20ZBd08ILnKcj7XKZkLU5FkoA0udEBvQ0f9QLNyyy3DZMCQWcwRuj1m73D sq8DEFBdZ5eEkj1dCyx+t/ga6x2rHyc8Sl86oK1tvAkwBNsfKou3v+jP/l14a7DGBvrmlYjO 59o3t6inu6H7pt7OL6u6BQj7DoMAEQEAAcLBfAQYAQgAJgIbDBYhBBvZyq1zXEw6Rg38yk3e EPcA/4NaBQJonNqrBQkmWAihAAoJEE3eEPcA/4NaKtMQALAJ8PzprBEXbXcEXwDKQu+P/vts IfUb1UNMfMV76BicGa5NCZnJNQASDP/+bFg6O3gx5NbhHHPeaWz/VxlOmYHokHodOvtL0WCC 8A5PEP8tOk6029Z+J+xUcMrJClNVFpzVvOpb1lCbhjwAV465Hy+NUSbbUiRxdzNQtLtgZzOV Zw7jxUCs4UUZLQTCuBpFgb15bBxYZ/BL9MbzxPxvfUQIPbnzQMcqtpUs21CMK2PdfCh5c4gS sDci6D5/ZIBw94UQWmGpM/O1ilGXde2ZzzGYl64glmccD8e87OnEgKnH3FbnJnT4iJchtSvx yJNi1+t0+qDti4m88+/9IuPqCKb6Stl+s2dnLtJNrjXBGJtsQG/sRpqsJz5x1/2nPJSRMsx9 5YfqbdrJSOFXDzZ8/r82HgQEtUvlSXNaXCa95ez0UkOG7+bDm2b3s0XahBQeLVCH0mw3RAQg r7xDAYKIrAwfHHmMTnBQDPJwVqxJjVNr7yBic4yfzVWGCGNE4DnOW0vcIeoyhy9vnIa3w1uZ 3iyY2Nsd7JxfKu1PRhCGwXzRw5TlfEsoRI7V9A8isUCoqE2Dzh3FvYHVeX4Us+bRL/oqareJ CIFqgYMyvHj7Q06kTKmauOe4Nf0l0qEkIuIzfoLJ3qr5UyXc2hLtWyT9Ir+lYlX9efqh7mOY qIws/H2t In-Reply-To: <20250926131527.3260733-1-sumanthk@linux.ibm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 26.09.25 15:15, Sumanth Korikkar wrote: > Hi, Hi, > > Patchset provides a new interface for dynamic configuration and > deconfiguration of hotplug memory on s390, allowing with/without > memmap_on_memory support. It is a follow up on the discussion with David > when introducing memmap_on_memory support for s390 and support dynamic > (de)configuration of memory: > https://lore.kernel.org/all/ee492da8-74b4-4a97-8b24-73e07257f01d@redhat.com/ > https://lore.kernel.org/all/20241202082732.3959803-1-sumanthk@linux.ibm.com/ > > The original motivation for introducing memmap_on_memory on s390 was to > avoid using online memory to store struct pages metadata, particularly > for standby memory blocks. This became critical in cases where there was > an imbalance between standby and online memory, potentially leading to > boot failures due to insufficient memory for metadata allocation. > > To address this, memmap_on_memory was utilized on s390. However, in its > current form, it adds struct pages metadata at the start of each memory > block at the time of addition (only standby memory), and this > configuration is static. It cannot be changed at runtime (When the user > needs continuous physical memory). > > Inorder to provide more flexibility to the user and overcome the above > limitation, add an option to dynamically configure and deconfigure > hotpluggable memory block with/without memmap_on_memory. This will cleanly add/remove the memory, including the directmap and other tracking data, so I like it. > > With the new interface, s390 will not add all possible hotplug memory in > advance, like before, to make it visible in sysfs for online/offline > actions. Instead, before memory block can be set online, it has to be > configured via a new interface in /sys/firmware/memory/memoryX/config, > which makes s390 similar to others. i.e. Adding of hotpluggable memory is > controlled by the user instead of adding it at boottime. Before I dig into the details, will onlining/offling still trigger hypervisor action, or does that now really happen when memory is added/removed? That would be really nice, because it would remove the whole need for "standby" memory, and having to treat hotplugged memory differently under LPAR/z/VM than anywhere else (-> keep it offline). > > s390 kernel sysfs interface to configure/deconfigure memory with > memmap_on_memory (with upcoming lsmem changes): > > * Initial memory layout: > lsmem -o RANGE,SIZE,STATE,BLOCK,CONFIGURED,MEMMAP_ON_MEMORY > RANGE SIZE STATE BLOCK CONFIGURED MEMMAP_ON_MEMORY > 0x00000000-0x7fffffff 2G online 0-15 yes no > 0x80000000-0xffffffff 2G offline 16-31 no yes Could we instead modify "STATE" to reflect that it is "not added" / "not configured" / "disabled" etc? Like lsmem -o RANGE,SIZE,STATE,BLOCK,MEMMAP_ON_MEMORY RANGE SIZE STATE BLOCK 0x00000000-0x7fffffff 2G online 0-15 0x80000000-0xffffffff 2G disabled 16-31 Or is that an attempt to maintain backwards compatibility? > > * Configure memory > echo 1 > /sys/firmware/memory/memory16/config The granularity here is also memory_block_size_bytes(), correct? > lsmem -o RANGE,SIZE,STATE,BLOCK,CONFIGURED,MEMMAP_ON_MEMORY > RANGE SIZE STATE BLOCK CONFIGURED MEMMAP_ON_MEMORY > 0x00000000-0x7fffffff 2G online 0-15 yes no > 0x80000000-0x87ffffff 128M offline 16 yes yes > 0x88000000-0xffffffff 1.9G offline 17-31 no yes > > * Deconfigure memory > echo 0 > /sys/firmware/memory/memory16/config > lsmem -o RANGE,SIZE,STATE,BLOCK,CONFIGURED,MEMMAP_ON_MEMORY > RANGE SIZE STATE BLOCK CONFIGURED MEMMAP_ON_MEMORY > 0x00000000-0x7fffffff 2G online 0-15 yes no > 0x80000000-0xffffffff 2G offline 16-31 no yes > > * Enable memmap_on_memory and online it. > (Deconfigure first) > echo 0 > /sys/devices/system/memory/memory5/online > echo 0 > /sys/firmware/memory/memory5/config > > lsmem -o RANGE,SIZE,STATE,BLOCK,CONFIGURED,MEMMAP_ON_MEMORY > RANGE SIZE STATE BLOCK CONFIGURED MEMMAP_ON_MEMORY > 0x00000000-0x27ffffff 640M online 0-4 yes no > 0x28000000-0x2fffffff 128M offline 5 no no > 0x30000000-0x7fffffff 1.3G online 6-15 yes no > 0x80000000-0xffffffff 2G offline 16-31 no yes > > (Enable memmap_on_memory and online it) > echo 1 > /sys/firmware/memory/memory5/memmap_on_memory > echo 1 > /sys/firmware/memory/memory5/config > echo 1 > /sys/devices/system/memory/memory5/online I guess the use for memmap_on_memory would now be limited to making hotplug more likely to succeed in OOM scenarios. > > lsmem -o RANGE,SIZE,STATE,BLOCK,CONFIGURED,MEMMAP_ON_MEMORY > RANGE SIZE STATE BLOCK CONFIGURED MEMMAP_ON_MEMORY > 0x00000000-0x27ffffff 640M online 0-4 yes no > 0x28000000-0x2fffffff 128M online 5 yes yes > 0x30000000-0x7fffffff 1.3G online 6-15 yes no > 0x80000000-0xffffffff 2G offline 16-31 no yes > > * Disable memmap_on_memory and online it. > (Deconfigure first) > echo 0 > /sys/devices/system/memory/memory5/online > echo 0 > /sys/firmware/memory/memory5/config > > lsmem -o RANGE,SIZE,STATE,BLOCK,CONFIGURED,MEMMAP_ON_MEMORY > RANGE SIZE STATE BLOCK CONFIGURED MEMMAP_ON_MEMORY > 0x00000000-0x27ffffff 640M online 0-4 yes no > 0x28000000-0x2fffffff 128M offline 5 no yes > 0x30000000-0x7fffffff 1.3G online 6-15 yes no > 0x80000000-0xffffffff 2G offline 16-31 no yes > > (Disable memmap_on_memory and online it) > echo 0 > /sys/firmware/memory/memory5/memmap_on_memory > echo 1 > /sys/firmware/memory/memory5/config > echo 1 > /sys/devices/system/memory/memory5/online > > lsmem -o RANGE,SIZE,STATE,BLOCK,CONFIGURED,MEMMAP_ON_MEMORY > RANGE SIZE STATE BLOCK CONFIGURED MEMMAP_ON_MEMORY > 0x00000000-0x7fffffff 2G online 0-15 yes no > 0x80000000-0xffffffff 2G offline 16-31 no yes > > * Userspace changes: > lsmem/chmem tool is also changed to use the new interface. I will send > it to util-linux soon. > > Patch 1 adds support for removal of boot-allocated memory blocks. > > Patch 2 provides option to dynamically configure and deconfigure memory > with/without memmap_on_memory. > > Patch 3 removes MHP_OFFLINE_INACCESSIBLE from s390. The mhp flag was > used to mark memory as not accessible until memory hotplug online phase > begins. However, with patch 2, it is no longer essential. Memory can be > brought to accessible state before adding memory, as the memory is added > during runttime now instead of boottime. Nice. > > Patch 4 removes the MEM_PREPARE_ONLINE/MEM_FINISH_OFFLINE notifiers. It > is no longer needed. Memory can be brought to accessible state before > adding memory now, with runtime (de)configuration of memory. Nice. -- Cheers David / dhildenb