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[149.14.88.26]) by smtp.gmail.com with ESMTPSA id fo4-20020a056000290400b0033af3294417sm6643931wrb.21.2024.01.31.03.06.59 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 31 Jan 2024 03:07:00 -0800 (PST) Message-ID: Date: Wed, 31 Jan 2024 12:06:59 +0100 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 00/15] mm/memory: optimize fork() with PTE-mapped THP Content-Language: en-US To: Ryan Roberts , linux-kernel@vger.kernel.org Cc: linux-mm@kvack.org, Andrew Morton , Matthew Wilcox , Russell King , Catalin Marinas , Will Deacon , Dinh Nguyen , Michael Ellerman , Nicholas Piggin , Christophe Leroy , "Aneesh Kumar K.V" , "Naveen N. Rao" , Paul Walmsley , Palmer Dabbelt , Albert Ou , Alexander Gordeev , Gerald Schaefer , Heiko Carstens , Vasily Gorbik , Christian Borntraeger , Sven Schnelle , "David S. Miller" , linux-arm-kernel@lists.infradead.org, linuxppc-dev@lists.ozlabs.org, linux-riscv@lists.infradead.org, linux-s390@vger.kernel.org, sparclinux@vger.kernel.org References: <20240129124649.189745-1-david@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: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 31.01.24 11:43, Ryan Roberts wrote: > On 29/01/2024 12:46, David Hildenbrand wrote: >> Now that the rmap overhaul[1] is upstream that provides a clean interface >> for rmap batching, let's implement PTE batching during fork when processing >> PTE-mapped THPs. >> >> This series is partially based on Ryan's previous work[2] to implement >> cont-pte support on arm64, but its a complete rewrite based on [1] to >> optimize all architectures independent of any such PTE bits, and to >> use the new rmap batching functions that simplify the code and prepare >> for further rmap accounting changes. >> >> We collect consecutive PTEs that map consecutive pages of the same large >> folio, making sure that the other PTE bits are compatible, and (a) adjust >> the refcount only once per batch, (b) call rmap handling functions only >> once per batch and (c) perform batch PTE setting/updates. >> >> While this series should be beneficial for adding cont-pte support on >> ARM64[2], it's one of the requirements for maintaining a total mapcount[3] >> for large folios with minimal added overhead and further changes[4] that >> build up on top of the total mapcount. >> >> Independent of all that, this series results in a speedup during fork with >> PTE-mapped THP, which is the default with THPs that are smaller than a PMD >> (for example, 16KiB to 1024KiB mTHPs for anonymous memory[5]). >> >> On an Intel Xeon Silver 4210R CPU, fork'ing with 1GiB of PTE-mapped folios >> of the same size (stddev < 1%) results in the following runtimes >> for fork() (shorter is better): >> >> Folio Size | v6.8-rc1 | New | Change >> ------------------------------------------ >> 4KiB | 0.014328 | 0.014035 | - 2% >> 16KiB | 0.014263 | 0.01196 | -16% >> 32KiB | 0.014334 | 0.01094 | -24% >> 64KiB | 0.014046 | 0.010444 | -26% >> 128KiB | 0.014011 | 0.010063 | -28% >> 256KiB | 0.013993 | 0.009938 | -29% >> 512KiB | 0.013983 | 0.00985 | -30% >> 1024KiB | 0.013986 | 0.00982 | -30% >> 2048KiB | 0.014305 | 0.010076 | -30% > > Just a heads up that I'm seeing some strange results on Apple M2. Fork for > order-0 is seemingly costing ~17% more. I'm using GCC 13.2 and was pretty sure I > didn't see this problem with version 1; although that was on a different > baseline and I've thrown the numbers away so will rerun and try to debug this. > So far, on my x86 tests (Intel, AMD EPYC), I was not able to observe this. fork() for order-0 was consistently effectively unchanged. Do you observe that on other ARM systems as well? > | kernel | mean_rel | std_rel | > |:------------|-----------:|----------:| > | mm-unstable | 0.0% | 1.1% | > | patch 1 | -2.3% | 1.3% | > | patch 10 | -2.9% | 2.7% | > | patch 11 | 13.5% | 0.5% | > | patch 12 | 15.2% | 1.2% | > | patch 13 | 18.2% | 0.7% | > | patch 14 | 20.5% | 1.0% | > | patch 15 | 17.1% | 1.6% | > | patch 15 | 16.7% | 0.8% | > > fork for order-9 is looking good (-20%), and for the zap series, munmap is > looking good, but dontneed is looking poor for both order-0 and 9. But one thing > at a time... let's concentrate on fork order-0 first. munmap and dontneed end up calling the exact same call paths. So a big performance difference is rather surprising and might indicate something else. (I think I told you that I was running in some kind of VMA merging problem where one would suddenly get with my benchmark 1 VMA per page. The new benchmark below works around that, but I am not sure if that was fixed in the meantime) VMA merging can of course explain a big difference in fork and munmap vs. dontneed times, especially when comparing different code base where that VMA merging behavior was different. > > Note that I'm still using the "old" benchmark code. Could you resend me the link > to the new code? Although I don't think there should be any effect for order-0 > anyway, if I understood your changes correctly? This is the combined one (small and large PTEs): https://gitlab.com/davidhildenbrand/scratchspace/-/raw/main/pte-mapped-folio-benchmarks.c?inline=false -- Cheers, David / dhildenb