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Thu, 11 Jul 2024 13:59:08 -0700 (PDT) Received: from [172.20.2.228] ([4.28.11.157]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-1fbb6a108a9sm54818295ad.61.2024.07.11.13.59.06 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 11 Jul 2024 13:59:07 -0700 (PDT) Message-ID: <6f045e34-8b88-49f7-957a-69130f6de949@redhat.com> Date: Thu, 11 Jul 2024 22:59:06 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v22 1/4] mm: add MAP_DROPPABLE for designating always lazily freeable mappings To: Yu Zhao Cc: "Jason A. Donenfeld" , Linus Torvalds , linux-kernel@vger.kernel.org, patches@lists.linux.dev, tglx@linutronix.de, linux-crypto@vger.kernel.org, linux-api@vger.kernel.org, x86@kernel.org, Greg Kroah-Hartman , Adhemerval Zanella Netto , Carlos O'Donell , Florian Weimer , Arnd Bergmann , Jann Horn , Christian Brauner , David Hildenbrand , linux-mm@kvack.org References: <98798483-dfcd-451e-94bb-57d830bf68d8@redhat.com> <54b6de32-f127-4928-9f4a-acb8653e5c81@redhat.com> <8586b19c-2e14-4164-888f-8c3b86f3f963@redhat.com> <443146f4-9db8-4a19-91f1-b6822fad8ce8@redhat.com> <1c8632b4-06a5-49da-be0c-6fc7ac2b3257@redhat.com> <2c464271-1c61-4cd8-bd4e-4bd8aa01fa00@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-Server: rspam12 X-Rspamd-Queue-Id: 07C961C001B X-Stat-Signature: 8xqr4to8agiunidai9rjratezsnohm7h X-Rspam-User: X-HE-Tag: 1720731551-74811 X-HE-Meta: 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 P7wurSHB drtyzMgQoKtSPW7BGssX6zkEP/2mDLsBnpPAItr0BTkw6Ig7IK5WYeMrADgA0KNWfExfDstSYOE4bfBijDleA6OaFaUOqu/IPOBXWmDNSJkR/rEiWHl5o13CO7hj3f8G7Wr2nc0Y4m81MZXIzlxNMtHV7w0iK+ckvxHxsYIYouNdeKKp62cvFJidyRmNhY5xg7gsOa/RFt5CJoV1qUlPkALoSFGYAdIvRFOwr2hrB0olcwnMvFA1WbAfEgH7SIUYFE1GiHVyLgnZEeGItgF/ZoLcmA98+h2QtW4ia4J7g8KSnBqF4bDqmzzLKbHwgPenHLF4bHQ+OtAby53Q3nM3/HdCg6jFuzprnB4dnoC/v0ulwfCVehclNVlq5Z2cQokARWAJo/ycU+DQjiNRiN/UhzvxYJ9w76KB+7FdnE2Hr/SLY2fSYmlWuSP15Qw== 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 11.07.24 21:58, Yu Zhao wrote: > On Thu, Jul 11, 2024 at 1:53 PM David Hildenbrand wrote: >> >> On 11.07.24 21:49, Yu Zhao wrote: >>> On Thu, Jul 11, 2024 at 1:20 PM David Hildenbrand wrote: >>>> >>>> On 11.07.24 21:18, David Hildenbrand wrote: >>>>> On 11.07.24 20:56, David Hildenbrand wrote: >>>>>> On 11.07.24 20:54, Jason A. Donenfeld wrote: >>>>>>> On Thu, Jul 11, 2024 at 08:24:07PM +0200, David Hildenbrand wrote: >>>>>>>>> And PG_large_rmappable seems to only be used for hugetlb branches. >>>>>>>> >>>>>>>> It should be set for THP/large folios. >>>>>>> >>>>>>> And it's tested too, apparently. >>>>>>> >>>>>>> Okay, well, how disappointing is this below? Because I'm running out of >>>>>>> tricks for flag reuse. >>>>>>> >>>>>>> diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h >>>>>>> index b9e914e1face..c1ea49a7f198 100644 >>>>>>> --- a/include/linux/page-flags.h >>>>>>> +++ b/include/linux/page-flags.h >>>>>>> @@ -110,6 +110,7 @@ enum pageflags { >>>>>>> PG_workingset, >>>>>>> PG_error, >>>>>>> PG_owner_priv_1, /* Owner use. If pagecache, fs may use*/ >>>>>>> + PG_owner_priv_2, >>>>>> >>>>>> Oh no, no new page flags please :) >>>>>> >>>>>> Maybe just follow what Linux suggested: pass vma to pte_dirty() and >>>>>> always return false for these special VMAs. >>>>> >>>>> ... or look into removing that one case that gives us headake. >>>>> >>>>> No idea what would happen if we do the following: >>>>> >>>>> CCing Yu Zhao. >>>>> >>>>> diff --git a/mm/vmscan.c b/mm/vmscan.c >>>>> index 0761f91b407f..d1dfbd4fd38d 100644 >>>>> --- a/mm/vmscan.c >>>>> +++ b/mm/vmscan.c >>>>> @@ -4280,14 +4280,9 @@ static bool sort_folio(struct lruvec *lruvec, struct folio *folio, struct scan_c >>>>> return true; >>>>> } >>>>> >>>>> - /* dirty lazyfree */ >>>>> - if (type == LRU_GEN_FILE && folio_test_anon(folio) && folio_test_dirty(folio)) { >>>>> - success = lru_gen_del_folio(lruvec, folio, true); >>>>> - VM_WARN_ON_ONCE_FOLIO(!success, folio); >>>>> - folio_set_swapbacked(folio); >>>>> - lruvec_add_folio_tail(lruvec, folio); >>>>> - return true; >>>>> - } >>>>> + /* lazyfree: we may not be allowed to set swapbacked: MAP_DROPPABLE */ >>>>> + if (type == LRU_GEN_FILE && folio_test_anon(folio) && folio_test_dirty(folio)) >>>>> + return false; >>> >>> This is an optimization to avoid an unnecessary trip to >>> shrink_folio_list(), so it's safe to delete the entire 'if' block, and >>> that would be preferable than leaving a dangling 'if'. >> >> Great, thanks. >> >>> >>>> Note that something is unclear to me: are we maybe running into that >>>> code also if folio_set_swapbacked() is already set and we are not in the >>>> lazyfree path (in contrast to what is documented)? >>> >>> Not sure what you mean: either rmap sees pte_dirty() and does >>> folio_mark_dirty() and then folio_set_swapbacked(); or MGLRU does the >>> same sequence, with the first two steps in walk_pte_range() and the >>> last one here. >> >> Let me rephrase: >> >> Checking for lazyfree is >> >> "folio_test_anon(folio) && !folio_test_swapbacked(folio)" >> >> Testing for dirtied lazyfree is >> >> "folio_test_anon(folio) && !folio_test_swapbacked(folio) && >> folio_test)dirty(folio)" >> >> So I'm wondering about the missing folio_test_swapbacked() test. > > It's not missing: type == LRU_GEN_FILE means folio_is_file_lru(), > which in turn means !folio_test_swapbacked(). > Ahh, got it, thanks! -- Cheers, David / dhildenb