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[2003:cb:c749:6600:b73a:466c:e610:686]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4366127c4b0sm23312375e9.35.2024.12.19.09.23.07 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 19 Dec 2024 09:23:07 -0800 (PST) Message-ID: Date: Thu, 19 Dec 2024 18:23:06 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm: add maybe_lru_add_drain() that only drains when threshold is exceeded To: Rik van Riel , Andrew Morton Cc: Chris Li , Ryan Roberts , "Matthew Wilcox (Oracle)" , linux-kernel@vger.kernel.org, linux-mm@kvack.org, kernel-team@meta.com References: <20241218115604.7e56bedb@fangorn> <189f4767-e7c2-4522-b943-b644126bf897@redhat.com> <58d69446edb0e2b3b4edec442043cd0a9748f15f.camel@surriel.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: <58d69446edb0e2b3b4edec442043cd0a9748f15f.camel@surriel.com> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: cdzJq6cEFu7vlMX1007gQtufgpNVHziMjrx0qrE_X5I_1734628989 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: F1311100018 X-Stat-Signature: mt5qcjd8e6gcb1137ctu5k85c4cafg9d X-Rspam-User: X-HE-Tag: 1734628927-4600 X-HE-Meta: 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 ErP4WDec XbsgytR3tYNPJRHBH3JL5Tq0Ans3MnKU1nOWMDiYiU4m38Yj+XDaBp2s5D/lqDcPMODtMDv8RoLzUHFdIXiz+LyqBzUDPj2UW8aedbCk51MQ71WqN8n/mQeE4MJ6q5m2TTP5+QhoMil0X+023+uNsQiQ63WXujd5J6uRR64TVlhvB5BSrgfdX6vsgqclsQl/pyHcObYQtveupPZKD6O970b+UTOnkhflctrKpDjCnB4uy59jn8bgtfWyX764gAuaHqwNddWJAOcR7WcRDpNx80Kr9wtvcGSBhi3jE8ilxOF/YX7OqyXoZaNyK3IiGJ8ZykdXYzOBEZnfxMZcMEE9WSQpwopxQDzMF22MAtyGKfk/d9Qt7hPEveFHjsDvW8AsnYdwWN5qBrRrCjAlT5rkC7Hs6eybpnAfcaFCYduF6hzLs41NGrye/GLLoSVPEeRa/OtKLHqi/oDIM6djVHVCYGwZDRA== 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 19.12.24 15:11, Rik van Riel wrote: > On Thu, 2024-12-19 at 14:47 +0100, David Hildenbrand wrote: >> >>> +++ b/mm/swap_state.c >>> @@ -317,7 +317,7 @@ void free_pages_and_swap_cache(struct >>> encoded_page **pages, int nr) >>>    struct folio_batch folios; >>>    unsigned int refs[PAGEVEC_SIZE]; >>> >>> - lru_add_drain(); >>> + maybe_lru_add_drain(); >> >> I'm wondering about the reason+effect of this existing call. >> >> Seems to date back to the beginning of git. >> >> Likely it doesn't make sense to have effectively-free pages in the >> LRU+mlock cache. But then, this only considers the local CPU >> LRU/mlock >> caches ... hmmm >> >> So .... do we need this at all? :) >> > That is a very good question. > > I think we need to free those pending pages at > some point. They can't accumulate there forever. > However, I am not sure where those points should > be. The number of entries are limited, so it will regularly be drained under normal system operation. Only if we manage to not place any pages on the local LRU cache, then they would in fact get stranded there until someone does a lru_add_drain_all(), or we perform another operation that calls lru_add_drain() on this CPU. I would assume memory reclaim would drain as well, and I see some calls in vmscan.c Interestingly, we only use the LRU cache for small folios. Even order-1 folios never strand there. So when freeing a bunch of large folios, draining might not make sense at all. > > I can think of a few considerations: > 1) We should consider approximate LRU ordering, > and move pages onto the LRU every once in a > while. > 2) When we are trying to free memory, we should> maybe ensure not too many pages are in these > temporary buffers? folio_batch_add() drains if folio_batch_space() returns 0 (no slots left). Apparently we have PAGEVEC_SIZE slots, which is 31 ... 31 * PAGE_SIZE stranded there. > 3) For lock batching reasons, we do not want to > drain these buffers too frequently. Yes. I know that we drain in places before we perform some action that requires these folios to be marked as LRU, for example, if we want to isolate them. > > My patch takes a small step in the direction of > more batching, but maybe we can take a larger one? Yes, this "drain on the page freeing path" looks a bit odd to me, but maybe there is a good reason why it's been around for decades ... :) -- Cheers, David / dhildenb