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[2003:cb:c706:d800:568a:6ea7:5272:797c]) by smtp.gmail.com with ESMTPSA id b13-20020a5d4d8d000000b003432d61d6b7sm12252425wru.51.2024.04.15.08.10.48 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 15 Apr 2024 08:10:49 -0700 (PDT) Message-ID: Date: Mon, 15 Apr 2024 17:10:48 +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: A98FC4000E X-Rspam-User: X-Rspamd-Server: rspam02 X-Stat-Signature: yfghjatbpag1bdysm1mhwa8esf13kqj1 X-HE-Tag: 1713193853-421742 X-HE-Meta: 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 F6M7m5iC eWL/mGJiFOV5pM/IXWKRfWpk07URV06G1iwzZJ0iGNiPC7bHH7T8GmzU4JLsE0MVDD2D6py8qND0h3MABpecBWG9BGpEFJFYqPDzbdNjCGSyCyLHwTMTrEtjyC43f9BuHmKieQkaSx+AGHYm24fwXf0Twy0dBYHI0rSUnZH7PSEk7CQAMLEVxZj7VvZHbL8J3lq/T1SIJU7+uBC31GWPsvhD8EZq+rM30W1Vlm/89YcEtOLsM/5ZFuwOWV7RcfnQrOaYzfyIHUU56mxM7tCO5TX00hqON4ylBtSihAlEJCT7mjAwdAtM6D7/XUzBtSfnyHm89N9KQKcq/Mpw9+wawQGvoxx78Gy30puILOSFc4zUQgZwiZC/07FkhJRiFXZCq8huhIdIT9YnVwDaxPVJ54/9KjuG8HtRXmttFOQCHx81sAAqpo97uIFjqpHws3Pj0TiMxKVUO0BJZruodydvq0SkaCQ== 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 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'll look into the virtio-mem case soonish and will let you know once I have something running. -- Cheers, David / dhildenb