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[2003:cb:c718:1300:9860:66a2:fe4d:c379]) by smtp.gmail.com with ESMTPSA id r4-20020a5d6944000000b00343b09729easm8346754wrw.69.2024.04.08.00.54.47 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 08 Apr 2024 00:54:48 -0700 (PDT) Message-ID: <7aec7b98-db81-4238-bdd6-afb69679f852@redhat.com> Date: Mon, 8 Apr 2024 09:54:47 +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 , Johannes Weiner Cc: 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> 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-Rspam-User: X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 30C5340005 X-Stat-Signature: qhpkxf7m5we3jg5r6wcey8yp9soc4u89 X-HE-Tag: 1712562892-454017 X-HE-Meta: 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 XilGIUmP 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 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 05.04.24 20:43, Yosry Ahmed wrote: > On Fri, Apr 5, 2024 at 8:26 AM Johannes Weiner wrote: >> >> On Fri, Apr 05, 2024 at 05:35:07AM +0000, Yosry Ahmed wrote: >>> Currently, we calculate the zswap global limit, and potentially the >>> acceptance threshold in the zswap, in pages in the zswap store path. >>> This is unnecessary because the values rarely change. >>> >>> Instead, precalculate the them when the module parameters are updated, >>> which should be rare. Since we are adding custom handlers for setting >>> the percentages now, add proper validation that they are <= 100. >>> >>> Suggested-by: Johannes Weiner >>> Signed-off-by: Yosry Ahmed >> >> Nice! Getting that stuff out of the hotpath! >> >> Two comments below: >> >>> @@ -684,6 +703,43 @@ static int zswap_enabled_param_set(const char *val, >>> return ret; >>> } >>> >>> +static int __zswap_percent_param_set(const char *val, >>> + const struct kernel_param *kp) >>> +{ >>> + unsigned int n; >>> + int ret; >>> + >>> + ret = kstrtouint(val, 10, &n); >>> + if (ret || n > 100) >>> + return -EINVAL; >>> + >>> + return param_set_uint(val, kp); >>> +} >>> + >>> +static int zswap_max_pool_param_set(const char *val, >>> + const struct kernel_param *kp) >>> +{ >>> + int err = __zswap_percent_param_set(val, kp); >>> + >>> + if (!err) { >>> + zswap_update_max_pages(); >>> + zswap_update_accept_thr_pages(); >>> + } >>> + >>> + return err; >>> +} >>> + >>> +static int zswap_accept_thr_param_set(const char *val, >>> + const struct kernel_param *kp) >>> +{ >>> + int err = __zswap_percent_param_set(val, kp); >>> + >>> + if (!err) >>> + zswap_update_accept_thr_pages(); >>> + >>> + return err; >>> +} >> >> I think you can keep this simple and just always update both if >> anything changes for whatever reason. It's an extremely rare event >> after all. That should cut it from 3 functions to 1. > > Yeah we can also combine both update functions in this case. > >> >> Note that totalram_pages can also change during memory onlining and >> offlining. For that you need a memory notifier that also calls that >> refresh function. It's simple enough, though, check out the code >> around register_memory_notifier() in drivers/xen/balloon.c. > > Good point, I completely missed this. It seems like totalram_pages can > actually change from contexts other than memory hotplug as well, > specifically through adjust_managed_page_count(), and mostly through > ballooning drivers. Do we trigger the notifiers in this case? I can't > find such logic. Things like virtio-balloon never online/offline memory and would never call it. Things like virtio-mem sometimes will online/offline memory and would sometimes call it (but not always). Things like the Hyper-V balloon and XEN balloon never offline memory, and would only call it when onlining memory. > > It seems like in this case the actual amount of memory does not > change, but the drivers take it away from the system. It makes some > sense to me that the zswap limits do not change in this case, > especially that userspace just sets those limits as a percentage of > total memory. I wouldn't expect userspace to take ballooning into > account here. > For virtio-mem, it does change ("actual amount of memory"). For virtio-balloon, it's tricky. When using virtio-balloon for VM resizing, it would similarly change. When using it for pure memory overcommit, it depends on whatever the policy in the hypervisor is ... might be that under memory pressure that memory is simply given back to the VM. > However, it would be a behavioral change from today where we always > rely on totalram_pages(). Also, if userspace happens to change the > limit when a driver is holding a big chunk of memory away from > totalram_pages, then the limit would be constantly underestimated. > > I do not have enough familiarity with memory ballooning to know for > sure if this is okay. How much memory can memory ballooning add/remove > from totalram_pages(), and is it usually transient or does it stick > around for a while? > > Also CCing David here. It can be a lot. Especially with the Hyper-V balloon (but also on environments where other forms of memory hotunplug are not supported), memory ballooning can be used to unplug memory. So that memory can be gone for good and it can end up being quite a lot of memory. The clean thing to do would be to have a way for other subsystems to get notified on any totalram_pages() changes, so they can adjust accordingly. -- Cheers, David / dhildenb