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[2003:cb:c72f:e500:e96a:8043:1211:8e6a]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-431bd947bf4sm194167225e9.27.2024.11.04.09.10.49 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 04 Nov 2024 09:10:50 -0800 (PST) Message-ID: Date: Mon, 4 Nov 2024 18:10:49 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2] mm: count zeromap read and set for swapout and swapin To: Johannes Weiner Cc: Barry Song <21cnbao@gmail.com>, akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Barry Song , Usama Arif , Chengming Zhou , Yosry Ahmed , Nhat Pham , Hugh Dickins , Matthew Wilcox , Shakeel Butt , Andi Kleen , Baolin Wang , Chris Li , "Huang, Ying" , Kairui Song , Ryan Roberts References: <20241102101240.35072-1-21cnbao@gmail.com> <20241104163402.GA810664@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: <20241104163402.GA810664@cmpxchg.org> 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: 7bit X-Rspamd-Server: rspam10 X-Stat-Signature: xpmxhp5nupfceazi186yy1qr1y91bmxa X-Rspamd-Queue-Id: B7BAE18001B X-Rspam-User: X-HE-Tag: 1730740232-663210 X-HE-Meta: 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 ZZXUOh1b JtoGD0bN+ej7sVJGAKq0VdR8trkcvkqvS4xCKBpGkf9wHYQVLJT1Q+1crt72hiYSr+gr/PclsDnIphH4nOe5XVxh8uaAFq6xtabGDCVrhtERu1tv5a7l3e5T6gjBHTsZGzA7jy24xLg4tJoTneTGzbxX2C+ONOEkx8qfWxKCuf6xnwg8t4/0ajUbpPoWwnSMOJTuK1dZ4teoDl+Q/MFWk6jkeMxoTpgTIE5hw4xk6vHOsbKDCKOsxwemGljTnFJAD0dnKOxVR//hYeRR91bm808eBkveVxxen28if4J9dJ7MjuzriII17csCPYvuJ9UR1l4OtRnlIwhX6LBRwNQbH4eycRYOA9yViyINbIjlqJmTCaujkJz1dp0CY3p3S6LGGnFSNqI24xrn0qLOzevDampJ/3A== 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 04.11.24 17:34, Johannes Weiner wrote: > On Mon, Nov 04, 2024 at 01:42:08PM +0100, David Hildenbrand wrote: >> On 02.11.24 11:12, Barry Song wrote: >>> @@ -1599,6 +1599,16 @@ The following nested keys are defined. >>> pglazyfreed (npn) >>> Amount of reclaimed lazyfree pages >>> >>> + swpin_zero >>> + Number of pages moved into memory with zero content, meaning no >>> + copy exists in the backend swapfile, allowing swap-in to avoid >>> + I/O read overhead. >>> + >>> + swpout_zero >>> + Number of pages moved out of memory with zero content, meaning no >>> + copy is needed in the backend swapfile, allowing swap-out to avoid >>> + I/O write overhead. >> >> Hm, can make it a bit clearer that this is a pure optimization and refer >> to the other counters? >> >> swpin_zero >> Portion of "pswpin" pages for which I/O was optimized out >> because the page content was detected to be zero during swapout. > > AFAICS the zeropages currently don't show up in pswpin/pswpout, so > these are independent counters, not subsets. Ah. now I understand the problem. The whole "move out of memory" "move into memory" here is quite confusing TBH. We're not moving anything, we're optimizing out the move completely ... yes, you could call it compression (below). > > I'm leaning towards Barry's side on the fixes tag. I think the documentation when to use the Fixes: tag is pretty clear. Introducing new counters can hardly be considered a bugfix. Missing to adjust some counters that *existing tools* would know/use might be IMO (below). > When zswap handled > the same-filled pages, we would count them in zswpin/out. From a user > POV, especially one using zswap, the behavior didn't change, but the > counts giving insight into this (potentially significant) VM activity > disappeared. This is arguably a regression. > >> swpout_zero >> Portion of "pswout" pages for which I/O was optimized out >> because the page content was detected to be zero. > > Are we sure we want to commit to the "zero" in the name here? Until > very recently, zswap optimized all same-filled pages. It's possible > somebody might want to bring that back down the line. Agreed. > > In reference to the above, I'd actually prefer putting them back into > zswpin/zswpout. Sure, they're not handled by zswap.c proper, but this > is arguably just an implementation detail; from a user POV this is > still just (a form of) compression in lieu of IO to the swap backend. > > IMO there is no need for coming up with a separate category. Just add > them to zswpin/zswpout and remove the CONFIG_ZSWAP guards from them? Would work for me, although it might be a bit confusing if no zswap is configured. Maybe just needs to be documented. -- Cheers, David / dhildenb