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[2003:cb:c708:9d00:edd9:835b:4bfb:2ce3]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-436612008casm49134655e9.14.2024.12.20.07.53.01 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 20 Dec 2024 07:53:02 -0800 (PST) Message-ID: <1b9285ba-4118-4572-9392-42ec6ba6728c@redhat.com> Date: Fri, 20 Dec 2024 16:53:01 +0100 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: [RFC PATCH 1/4] mm/memory_hotplug: Add interface for runtime (de)configuration of memory To: Sumanth Korikkar Cc: linux-mm , Andrew Morton , Oscar Salvador , Gerald Schaefer , Heiko Carstens , Vasily Gorbik , Alexander Gordeev , linux-s390 , LKML References: <20241202082732.3959803-1-sumanthk@linux.ibm.com> <20241202082732.3959803-2-sumanthk@linux.ibm.com> <3151b9a0-3e96-4820-b6af-9f9ec4996ee1@redhat.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 ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwZgEEwEIAEICGwMGCwkIBwMCBhUIAgkKCwQW AgMBAh4BAheAAhkBFiEEG9nKrXNcTDpGDfzKTd4Q9wD/g1oFAl8Ox4kFCRKpKXgACgkQTd4Q 9wD/g1oHcA//a6Tj7SBNjFNM1iNhWUo1lxAja0lpSodSnB2g4FCZ4R61SBR4l/psBL73xktp rDHrx4aSpwkRP6Epu6mLvhlfjmkRG4OynJ5HG1gfv7RJJfnUdUM1z5kdS8JBrOhMJS2c/gPf wv1TGRq2XdMPnfY2o0CxRqpcLkx4vBODvJGl2mQyJF/gPepdDfcT8/PY9BJ7FL6Hrq1gnAo4 3Iv9qV0JiT2wmZciNyYQhmA1V6dyTRiQ4YAc31zOo2IM+xisPzeSHgw3ONY/XhYvfZ9r7W1l pNQdc2G+o4Di9NPFHQQhDw3YTRR1opJaTlRDzxYxzU6ZnUUBghxt9cwUWTpfCktkMZiPSDGd KgQBjnweV2jw9UOTxjb4LXqDjmSNkjDdQUOU69jGMUXgihvo4zhYcMX8F5gWdRtMR7DzW/YE BgVcyxNkMIXoY1aYj6npHYiNQesQlqjU6azjbH70/SXKM5tNRplgW8TNprMDuntdvV9wNkFs 9TyM02V5aWxFfI42+aivc4KEw69SE9KXwC7FSf5wXzuTot97N9Phj/Z3+jx443jo2NR34XgF 89cct7wJMjOF7bBefo0fPPZQuIma0Zym71cP61OP/i11ahNye6HGKfxGCOcs5wW9kRQEk8P9 M/k2wt3mt/fCQnuP/mWutNPt95w9wSsUyATLmtNrwccz63XOwU0EVcufkQEQAOfX3n0g0fZz Bgm/S2zF/kxQKCEKP8ID+Vz8sy2GpDvveBq4H2Y34XWsT1zLJdvqPI4af4ZSMxuerWjXbVWb T6d4odQIG0fKx4F8NccDqbgHeZRNajXeeJ3R7gAzvWvQNLz4piHrO/B4tf8svmRBL0ZB5P5A 2uhdwLU3NZuK22zpNn4is87BPWF8HhY0L5fafgDMOqnf4guJVJPYNPhUFzXUbPqOKOkL8ojk CXxkOFHAbjstSK5Ca3fKquY3rdX3DNo+EL7FvAiw1mUtS+5GeYE+RMnDCsVFm/C7kY8c2d0G NWkB9pJM5+mnIoFNxy7YBcldYATVeOHoY4LyaUWNnAvFYWp08dHWfZo9WCiJMuTfgtH9tc75 7QanMVdPt6fDK8UUXIBLQ2TWr/sQKE9xtFuEmoQGlE1l6bGaDnnMLcYu+Asp3kDT0w4zYGsx 5r6XQVRH4+5N6eHZiaeYtFOujp5n+pjBaQK7wUUjDilPQ5QMzIuCL4YjVoylWiBNknvQWBXS lQCWmavOT9sttGQXdPCC5ynI+1ymZC1ORZKANLnRAb0NH/UCzcsstw2TAkFnMEbo9Zu9w7Kv AxBQXWeXhJI9XQssfrf4Gusdqx8nPEpfOqCtbbwJMATbHyqLt7/oz/5deGuwxgb65pWIzufa N7eop7uh+6bezi+rugUI+w6DABEBAAHCwXwEGAEIACYCGwwWIQQb2cqtc1xMOkYN/MpN3hD3 AP+DWgUCXw7HsgUJEqkpoQAKCRBN3hD3AP+DWrrpD/4qS3dyVRxDcDHIlmguXjC1Q5tZTwNB boaBTPHSy/Nksu0eY7x6HfQJ3xajVH32Ms6t1trDQmPx2iP5+7iDsb7OKAb5eOS8h+BEBDeq 3ecsQDv0fFJOA9ag5O3LLNk+3x3q7e0uo06XMaY7UHS341ozXUUI7wC7iKfoUTv03iO9El5f XpNMx/YrIMduZ2+nd9Di7o5+KIwlb2mAB9sTNHdMrXesX8eBL6T9b+MZJk+mZuPxKNVfEQMQ a5SxUEADIPQTPNvBewdeI80yeOCrN+Zzwy/Mrx9EPeu59Y5vSJOx/z6OUImD/GhX7Xvkt3kq Er5KTrJz3++B6SH9pum9PuoE/k+nntJkNMmQpR4MCBaV/J9gIOPGodDKnjdng+mXliF3Ptu6 3oxc2RCyGzTlxyMwuc2U5Q7KtUNTdDe8T0uE+9b8BLMVQDDfJjqY0VVqSUwImzTDLX9S4g/8 kC4HRcclk8hpyhY2jKGluZO0awwTIMgVEzmTyBphDg/Gx7dZU1Xf8HFuE+UZ5UDHDTnwgv7E th6RC9+WrhDNspZ9fJjKWRbveQgUFCpe1sa77LAw+XFrKmBHXp9ZVIe90RMe2tRL06BGiRZr jPrnvUsUUsjRoRNJjKKA/REq+sAnhkNPPZ/NNMjaZ5b8Tovi8C0tmxiCHaQYqj7G2rgnT0kt WNyWQQ== Organization: Red Hat In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 03.12.24 15:33, Sumanth Korikkar wrote: > On Mon, Dec 02, 2024 at 05:55:19PM +0100, David Hildenbrand wrote: >> Hi! >> >> Not completely what I had in mind, especially not that we need something >> that generic without any indication of ranges :) >> >> In general, the flow is as follows: >> >> 1) Driver detects memory and adds it >> 2) Something auto-onlines that memory (e.g., udev rule) >> >> For dax/kmem, 1) can be controlled using devdax, and usually it also tries >> to take care of 2). >> >> s390x standby storage really is the weird thing here, because it does 1) and >> doesn't want 2). It shouldn't do 1) until a user wants to make use of >> standby memory. > > Hi David, Hi, sorry for the late reply. Cleaning up (some of) my inbox before Christmas, and I realized I skipped this mail. > > The current rfc design doesnt do 1) until user initiates it. > > The current rfc design considers the fact that there cannot be memory > holes, when there is a availability of standby memory. (which holds true > for both lpars and zvms) > > With number of online and standby memory ranges count > (max_configurable), prototype lsmem/chmem could determine memory ranges > which are not yet configured > i.e. (configurable_memory = max_configurable - online ranges from sysfs > /sys/devices/system/memory/memory*). > > Example prototype implementation of lsmem/chmem looks like: > ./lsmem -o RANGE,SIZE,STATE,BLOCK,ALTMAP > RANGE SIZE STATE BLOCK ALTMAP > 0x0000000000000000-0x00000002ffffffff 12G online 0-95 0 > 0x0000000300000000-0x00000003ffffffff 4G deconfigured 96-127 - > > # Configure range with altmap > ./chmem -c 0x0000000300000000-0x00000003ffffffff -a > ./lsmem -o RANGE,SIZE,STATE,BLOCK,ALTMAP > RANGE SIZE STATE BLOCK ALTMAP > 0x0000000000000000-0x00000002ffffffff 12G online 0-95 0 > 0x0000000300000000-0x00000003ffffffff 4G offline 96-127 1 > > > # Online range > ./chmem -e 0x0000000300000000-0x00000003ffffffff && > ./lsmem -o RANGE,SIZE,STATE,BLOCK,ALTMAP > RANGE SIZE STATE BLOCK ALTMAP > 0x0000000000000000-0x00000002ffffffff 12G online 0-95 0 > 0x0000000300000000-0x00000003ffffffff 4G online 96-127 1 > > Memory block size: 128M > Total online memory: 16G > Total offline memory: 0B > Total deconfigured: 0B > > # offline range > ./chmem -d 0x0000000300000000-0x00000003ffffffff && > ./lsmem -o RANGE,SIZE,STATE,BLOCK,ALTMAP > RANGE SIZE STATE BLOCK ALTMAP > 0x0000000000000000-0x00000002ffffffff 12G online 0-95 0 > 0x0000000300000000-0x00000003ffffffff 4G offline 96-127 1 > > Memory block size: 128M > Total online memory: 12G > Total offline memory: 4G > Total deconfigured: 0B > > # Defconfigure range. > ./chmem -g 0x0000000300000000-0x00000003ffffffff && > ./lsmem -o RANGE,SIZE,STATE,BLOCK,ALTMAP > RANGE SIZE STATE BLOCK ALTMAP > 0x0000000000000000-0x00000002ffffffff 12G online 0-95 0 > 0x0000000300000000-0x00000003ffffffff 4G deconfigured 96-127 - > > Memory block size: 128M > Total online memory: 12G > Total offline memory: 0B > Total deconfigured: 4G Maybe "standby memory" might make it clearer. The concept is s390x specific, and it will likely stay s390x specific. I like the idea (frontend/tool interface), all we need is a way for these commands to detect ranges and turn them from standby into usable memory. > > The user can still determine the available memory ranges and make them > configurable using tools like lsmem or chmem with this approach atleast > on s390 with this approach. > >> My thinking was that s390x would expose the standby memory ranges somewhere >> arch specific in sysfs. From there, one could simply trigger the adding >> (maybe specifying e.g, memmap_on_memory) of selected ranges. > > As far as I understand, sysfs interface limits the size of the buffer > used in show() to 4kb. sysfs want usually "one value per file". > When there are huge number of standby memory > ranges, wouldnt it be an issue to display everything in one attribute? I was rather wondering about a syfs directory structure that exposes this information. For example, in the granularity of storage increments we can enable/disable. In general, it could be a similar structure as /sys/devices/system/memory/ (one director = one standby storage increment we can enable/disable?), but residing on the s390x specific sysfs area. Or any other way to express ranges that can be enabled/disabled as one unit. I'm not sure if extending /sys/devices/system/memory/ itself would be a good idea, though. It all is very s390x specific. > > Or use sysfs binary attributes to overcome the limitation? > > Please correct me, If I am wrong. > > Questions: > 1. If we go ahead with this sysfs interface approach to list all standby > memory ranges, could the list be made available via > /sys/devices/system/memory/configurable_memlist? This could be helpful, > as /sys/devices/system/memory/configure_memory performs architecture > independent checks and could also be useful for other architectures in > the future. See above, I think we want this s390x specific. > > 2. Whether the new interface should also be compatible with lsmem/chmem? Yes, likely we should allow them to query-configure this s390x specific thing. > > 3. OR can we have a s390 specific path (eg: > /sys/firmware/memory/standy_range) to list all standby memory range > which are in deconfigured state and also use the current design > (max_configurable) to make it easier for lsmem/chmem tool to detect > these standby memory ranges? Ah, there it is, yes! > >> To disable standby memory, one would first offline the memory to then >> trigger removal using the arch specific interface. It is very similar to >> dax/kmem's way of handling offline+removal. > > ok > >> Now I wonder if dax/kmem could be (ab)used on s390x for standby storage. >> Likely a simple sysfs interface could be easier to implement. > > I havent checked dax/kmem in detail yet. I will look into it. Probably it's not 100% what you want to achieve, just to give you an example how similar (but different) technologies have solved this problem. -- Cheers, David / dhildenb