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[2003:cb:c707:3500:5cd0:78d9:ca49:21f3]) by smtp.gmail.com with ESMTPSA id j27-20020a05600c1c1b00b00412f83e0c11sm5236707wms.22.2024.03.08.00.55.52 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 08 Mar 2024 00:55:52 -0800 (PST) Message-ID: <0530d101-b636-402e-991f-bc186b45490c@redhat.com> Date: Fri, 8 Mar 2024 09:55:51 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [LSF/MM/BPF TOPIC] Swap Abstraction "the pony" To: Barry Song <21cnbao@gmail.com>, Chris Li Cc: lsf-pc@lists.linux-foundation.org, linux-mm , ryan.roberts@arm.com, Chuanhua Han References: 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: rspam12 X-Rspamd-Queue-Id: 3D320C0004 X-Stat-Signature: xxw8i7qdxcngu484ohejnqxtb8wgyukb X-HE-Tag: 1709888158-303327 X-HE-Meta: U2FsdGVkX18MEcDp+L1mUSK9NOCG6KhnFrnuaQCjARQCw2mc0DYTz6lquwHa+OemYUZB9gCMYzqnZZvE8y31RW7F6ad6WT55TSrDkybwP5YP/y3VJEunpyZFh6czqk+iqd0gUdKQ7S9f3plmCY3JO9wGZVpDx2YbmyyPAx9zgcmhZrzvQ0RwQhqOW8sCLuZgUWW77nOLEkeJJgGuOrWHJWyrcVqV4wVYtSUtiHNGFLePyC4SGfW8w/R7kwsz2Qe7CUWUTePDgMCWY60Xa5g44Q23wRGwufoptCYQ+Ai5WoOKriD5iQTFdlZFlWEYm09pZnIcv8p3zblrPmeAVkgNIgZAuwbltP/fnWv0nUgThL579Zp1tcD8q+vkxzJLB+Kq7jrYRtPI4FhzgAe/X+sNoyGBwLTk/MUYOEqT5IGzoRzLw4EE4LLM2P+Qe7aqv9lomQXraUK1+rJUuSwGb9sv6bWp5yNByRli6UvPEGnkVmkP11PUDPQg94XnIrVc23A6vqhF5SAhBM/5/pSEqCcpzBtGnp9bD7Uz9HyzjJwlEqqToqtgiBaq7k8A9FFouNI/i3Ok/nBLxTHJ/+JksZGp3CA04BRK501BbIfFubDdhxlaR+4485BK0eNE4KoOlSSwEJr+mdCRU5DgR4lwF9kwvaXQpmgr9fI4g6aD+eESt29Zy3Rq7l4ZfKtg36rNlFW3xh12XM93+WChmkA5EI/WcOYpHr+5tTTcc/gQrIh3sGRRW/bQq4p4WfMHI4o9Gex4wgmtcmEZFE3z5Tz+xiLLpVqcF2Ukw9oLmW+4PiIAQjJJS8im6ko06wWLfhNPga/haCIn4K7Ty9V/zkShKVT1ye69xZESr5c6z51rn+CRoTUaeRLxxLsGdrALannuDk3kyXY59kGc5eRO5TyD5/TTtWllDeQdYCqwAA1+p7HRfwgKqAS5+xTuD2iFN49mvl6UfhF2qOX4C3R3grN9Pl9 h4HsRLw8 5OEyjKYWIdywBMLEfP/A09bFi00SiOfkA+HYpwUWa0uWU1C6elVruV726huis+dXIEOx/S3Gu62BBEBBf55S+3hZvm8oVKZ2MahS2CDGCSUq7KvHWv3R+S4raGa3erym/rq/3RYNOVkw+HhD65Na03degcTwBXZBz+ovczUDZ4BWzjReyWj5l+PHxt4lfGHs9NmoGclp/nH7PctoKQZRoZ8jyeTClAH8AoDCSeTmgoj6cqxjAE6oUKqw0YlNDf+QKTVjeMJQjS9kQUVf9yHX+5ao+skogLpS82P31lTmuwPXoxWrslCpzk+O3JwwsWWKjmLve/iFkq8I04dq5+dtLWTC3fNQfdRFiwmqSlKo3DHDfdEvfKOJ6Wqs/K2RxVsH7IGPG0IPWmVJpTPtdMp/FfgOQ62T1IyJ/wIIhjTkoqcqrjRAvMAChwEk/wxnFvnzj1kcaO1AId/YEFboLDvtR68/OyheF09f5KRj7rcvzoHO6HiAAgMMAFMJlac1di+NqOnphZ9vrkClrEHmcUq4A0rQEQw== 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 06.03.24 07:05, Barry Song wrote: > On Wed, Mar 6, 2024 at 4:00 PM Chris Li wrote: >> >> On Tue, Mar 5, 2024 at 5:15 PM Barry Song <21cnbao@gmail.com> wrote: >>>> Another limitation I would like to address is that swap_writepage can >>>> only write out IO in one contiguous chunk, not able to perform >>>> non-continuous IO. When the swapfile is close to full, it is likely >>>> the unused entry will spread across different locations. It would be >>>> nice to be able to read and write large folio using discontiguous disk >>>> IO locations. >>> >>> I don't find it will be too difficult for swap_writepage to only write >>> out a large folio which has discontiguous swap offsets. taking >>> zRAM as an example, as long as bio can be organized correctly, >>> zram should be able to write a large folio one by one for its all >>> subpages. >> >> Yes. >> >>> >>> static void zram_bio_write(struct zram *zram, struct bio *bio) >>> { >>> unsigned long start_time = bio_start_io_acct(bio); >>> struct bvec_iter iter = bio->bi_iter; >>> >>> do { >>> u32 index = iter.bi_sector >> SECTORS_PER_PAGE_SHIFT; >>> u32 offset = (iter.bi_sector & (SECTORS_PER_PAGE - 1)) << >>> SECTOR_SHIFT; >>> struct bio_vec bv = bio_iter_iovec(bio, iter); >>> >>> bv.bv_len = min_t(u32, bv.bv_len, PAGE_SIZE - offset); >>> >>> if (zram_bvec_write(zram, &bv, index, offset, bio) < 0) { >>> atomic64_inc(&zram->stats.failed_writes); >>> bio->bi_status = BLK_STS_IOERR; >>> break; >>> } >>> >>> zram_slot_lock(zram, index); >>> zram_accessed(zram, index); >>> zram_slot_unlock(zram, index); >>> >>> bio_advance_iter_single(bio, &iter, bv.bv_len); >>> } while (iter.bi_size); >>> >>> bio_end_io_acct(bio, start_time); >>> bio_endio(bio); >>> } >>> >>> right now , add_to_swap() is lacking a way to record discontiguous >>> offset for each subpage, alternatively, we have a folio->swap. >>> >>> I wonder if we can somehow make it page granularity, for each >>> subpage, it can have its own offset somehow like page->swap, >>> then in swap_writepage(), we can make a bio with multiple >>> discontiguous I/O index. then we allow add_to_swap() to get >>> nr_pages different swap offsets, and fill into each subpage. >> >> The key is where to store the subpage offset. It can't be stored on >> the tail page's page->swap because some tail page's page struct are >> just mapping of the head page's page struct. I am afraid this mapping >> relationship has to be stored on the swap back end. That is the idea, >> have swap backend keep track of an array of subpage's swap location. >> This array is looked up by the head swap offset. > > I assume "some tail page's page struct are just mapping of the head > page's page struct" is only true of hugeTLB larger than PMD-mapped > hugeTLB (for example 2MB) for this moment? more widely mTHP > less than PMD-mapped size will still have all tail page struct? We just successfully stopped using subpages to store swap offsets, and even accidentally fixed a bug that was lurking for years. I am confident that we don't want to go back. The current direction is to move as much information we can out of the subpages: So if we can find ways to avoid messing with subpages, that would be great. -- Cheers, David / dhildenb