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[2003:cb:c706:d800:568a:6ea7:5272:797c]) by smtp.gmail.com with ESMTPSA id i10-20020adffc0a000000b003456c693fa4sm12812933wrr.93.2024.04.15.12.15.25 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 15 Apr 2024 12:15:26 -0700 (PDT) Message-ID: <11e9143f-67c6-4d7a-827b-dd04043b6fa4@redhat.com> Date: Mon, 15 Apr 2024 21:15:25 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 2/5] mm: zswap: calculate limits only when updated To: Yosry Ahmed Cc: Johannes Weiner , Andrew Morton , Nhat Pham , Chengming Zhou , linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20240405053510.1948982-1-yosryahmed@google.com> <20240405053510.1948982-3-yosryahmed@google.com> <20240405152619.GA866431@cmpxchg.org> <7aec7b98-db81-4238-bdd6-afb69679f852@redhat.com> <69dcd33b-e8de-4927-93dd-d4ea22834a18@redhat.com> From: David Hildenbrand 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: 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: 8bit X-Rspamd-Queue-Id: 03FAE40005 X-Rspam-User: X-Rspamd-Server: rspam02 X-Stat-Signature: 6nzdryr5tywu3t9qo4xofwh9znqq17y6 X-HE-Tag: 1713208529-729366 X-HE-Meta: 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 /GaOZy4S nPHYvylSaYk3B/1hKk1CCBsxGRltjMtHbFWSxtNCKPMDoPBfCubknLhuRgT96BD0lCgk+Vyl0FBkJip9NvvR6UCz+WgvjMgig6+J+NDJF12s6YOvidW+9U/XOfpJ57ZGm3hiQeZYBWww7fOcVTW2JQapZjNpabjzmuL41 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: List-Subscribe: List-Unsubscribe: On 15.04.24 20:30, Yosry Ahmed wrote: > On Mon, Apr 15, 2024 at 8:10 AM David Hildenbrand wrote: >> >> On 13.04.24 03:05, Yosry Ahmed wrote: >>> On Fri, Apr 12, 2024 at 12:48 PM David Hildenbrand wrote: >>>> >>>> On 10.04.24 02:52, Yosry Ahmed wrote: >>>>> [..] >>>>>>> Do we need a separate notifier chain for totalram_pages() updates? >>>>>> >>>>>> Good question. I actually might have the requirement to notify some arch >>>>>> code (s390x) from virtio-mem when fake adding/removing memory, and >>>>>> already wondered how to best wire that up. >>>>>> >>>>>> Maybe we can squeeze that into the existing notifier chain, but needs a >>>>>> bit of thought. >>>>> >>>> >>>> Sorry for the late reply, I had to think about this a bit. >>>> >>>>> Do you mean by adding new actions (e.g. MEM_FAKE_ONLINE, >>>>> MEM_FAKE_OFFLINE), or by reusing the existing actions (MEM_ONLINE, >>>>> MEM_OFFLINE, etc). >>>> >>>> At least for virtio-mem, I think we could have a MEM_ONLINE/MEM_OFFLINE >>>> that prepare the whole range belonging to the Linux memory block >>>> (/sys/devices/system/memory/memory...) to go online, and then have >>>> something like MEM_SOFT_ONLINE/MEM_SOFT_OFFLINE or >>>> ENABLE_PAGES/DISABLE_PAGES ... notifications when parts become usable >>>> (!PageOffline, handed to the buddy) or unusable (PageOffline, removed >>>> from the buddy). >>>> >>>> There are some details to be figured out, but it could work. >>>> >>>> And as virtio-mem currently operates in pageblock granularity (e.g., 2 >>>> MiB), but frequently handles multiple contiguous pageblocks within a >>>> Linux memory block, it's not that bad. >>>> >>>> >>>> But the issue I see with ballooning is that we operate here often on >>>> page granularity. While we could optimize some cases, we might get quite >>>> some overhead from all the notifications. Alternatively, we could send a >>>> list of pages, but it won't win a beauty contest. >>>> >>>> I think the main issue is that, for my purpose (virtio-mem on s390x), I >>>> need to notify about the exact memory ranges (so I can reinitialize >>>> stuff in s390x code when memory gets effectively re-enabled). For other >>>> cases (total pages changing), we don't need the memory ranges, but only >>>> the "summary" -- or a notification afterwards that the total pages were >>>> just changed quite a bit. >>> >>> >>> Thanks for shedding some light on this. Although I am not familiar >>> with ballooning, sending notifications on page granularity updates >>> sounds terrible. It seems like this is not as straightforward as I had >>> anticipated. >>> >>> I was going to take a stab at this, but given that the motivation is a >>> minor optimization on the zswap side, I will probably just give up :) >> >> Oh no, so I have to do the work! ;) >> >>> >>> For now, I will drop this optimization from the series for now, and I >>> can revisit it if/when notifications for totalram_pages() are >>> implemented at some point. Please CC me if you do so for the s390x use >>> case :) >> >> I primarily care about virtio-mem resizing VM memory and adjusting >> totalram_pages(), memory ballooning for that is rather a hack for that >> use case ... so we're in agreement :) >> >> Likely we'd want two notification mechanisms, but no matter how I look >> at it, it's all a bit ugly. > > I am assuming you mean one with exact memory ranges for your s390x use > case, and one high-level mechanism for totalram_pages() updates -- or > did I miss the point? No, that's it. > > I am interested to see how page granularity updates would be handled > in this case. Perhaps they are only relevant for the high-level > mechanism? In that case, I suppose we can batch updates and notify > once when a threshold is crossed or something. Yes, we'd batch updates. -- Cheers, David / dhildenb