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[2003:cb:c717:a000:d4df:4b8f:37d4:59e4]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-35dd062eba2sm1610511f8f.77.2024.05.31.04.08.32 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 31 May 2024 04:08:32 -0700 (PDT) Message-ID: <87ac9610-5650-451f-aa54-e634a6310af4@redhat.com> Date: Fri, 31 May 2024 13:08:31 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH] mm: swap: reuse exclusive folio directly instead of wp page faults To: Barry Song <21cnbao@gmail.com>, akpm@linux-foundation.org, linux-mm@kvack.org Cc: chrisl@kernel.org, surenb@google.com, kasong@tencent.com, minchan@kernel.org, willy@infradead.org, ryan.roberts@arm.com, linux-kernel@vger.kernel.org, Barry Song References: <20240531104819.140218-1-21cnbao@gmail.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: <20240531104819.140218-1-21cnbao@gmail.com> 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-Stat-Signature: 7s1xy9up16qgi46h1csdfccq8a7483bw X-Rspamd-Queue-Id: E2EE84000B X-Rspam-User: X-Rspamd-Server: rspam10 X-HE-Tag: 1717153716-30549 X-HE-Meta: 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 +KJNvhOM 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 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 31.05.24 12:48, Barry Song wrote: > From: Barry Song > > After swapping out, we perform a swap-in operation. If we first read > and then write, we encounter a major fault in do_swap_page for reading, > along with additional minor faults in do_wp_page for writing. However, > the latter appears to be unnecessary and inefficient. Instead, we can > directly reuse in do_swap_page and completely eliminate the need for > do_wp_page. > > This patch achieves that optimization specifically for exclusive folios. > The following microbenchmark demonstrates the significant reduction in > minor faults. > > #define DATA_SIZE (2UL * 1024 * 1024) > #define PAGE_SIZE (4UL * 1024) > > static void *read_write_data(char *addr) > { > char tmp; > > for (int i = 0; i < DATA_SIZE; i += PAGE_SIZE) { > tmp = *(volatile char *)(addr + i); > *(volatile char *)(addr + i) = tmp; > } > } > > int main(int argc, char **argv) > { > struct rusage ru; > > char *addr = mmap(NULL, DATA_SIZE, PROT_READ | PROT_WRITE, > MAP_ANONYMOUS | MAP_PRIVATE, -1, 0); > memset(addr, 0x11, DATA_SIZE); > > do { > long old_ru_minflt, old_ru_majflt; > long new_ru_minflt, new_ru_majflt; > > madvise(addr, DATA_SIZE, MADV_PAGEOUT); > > getrusage(RUSAGE_SELF, &ru); > old_ru_minflt = ru.ru_minflt; > old_ru_majflt = ru.ru_majflt; > > read_write_data(addr); > getrusage(RUSAGE_SELF, &ru); > new_ru_minflt = ru.ru_minflt; > new_ru_majflt = ru.ru_majflt; > > printf("minor faults:%ld major faults:%ld\n", > new_ru_minflt - old_ru_minflt, > new_ru_majflt - old_ru_majflt); > } while(0); > > return 0; > } > > w/o patch, > / # ~/a.out > minor faults:512 major faults:512 > > w/ patch, > / # ~/a.out > minor faults:0 major faults:512 > > Minor faults decrease to 0! > > Signed-off-by: Barry Song > --- > mm/memory.c | 7 ++++--- > 1 file changed, 4 insertions(+), 3 deletions(-) > > diff --git a/mm/memory.c b/mm/memory.c > index eef4e482c0c2..e1d2e339958e 100644 > --- a/mm/memory.c > +++ b/mm/memory.c > @@ -4325,9 +4325,10 @@ vm_fault_t do_swap_page(struct vm_fault *vmf) > */ > if (!folio_test_ksm(folio) && > (exclusive || folio_ref_count(folio) == 1)) { > - if (vmf->flags & FAULT_FLAG_WRITE) { > - pte = maybe_mkwrite(pte_mkdirty(pte), vma); > - vmf->flags &= ~FAULT_FLAG_WRITE; > + if (vma->vm_flags & VM_WRITE) { > + pte = pte_mkwrite(pte_mkdirty(pte), vma); > + if (vmf->flags & FAULT_FLAG_WRITE) > + vmf->flags &= ~FAULT_FLAG_WRITE; This implies, that even on a read fault, you would mark the pte dirty and it would have to be written back to swap if still in the swap cache and only read. That is controversial. What is less controversial is doing what mprotect() via change_pte_range()/can_change_pte_writable() would do: mark the PTE writable but not dirty. I suggest setting the pte only dirty if FAULT_FLAG_WRITE is set. -- Cheers, David / dhildenb