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[2003:cb:c717:a000:d4df:4b8f:37d4:59e4]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4212b85c61dsm23553845e9.28.2024.05.31.05.10.33 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 31 May 2024 05:10:34 -0700 (PDT) Message-ID: Date: Fri, 31 May 2024 14:10:33 +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> Cc: akpm@linux-foundation.org, linux-mm@kvack.org, 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> <87ac9610-5650-451f-aa54-e634a6310af4@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-Rspam-User: X-Stat-Signature: sbe9413pgwqzbsxy43bj813hd687wojs X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 6733820013 X-HE-Tag: 1717157439-159674 X-HE-Meta: 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 RwzBMwzG 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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 13:55, Barry Song wrote: > On Fri, May 31, 2024 at 11:08 PM David Hildenbrand wrote: >> >> 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. > > Thanks! > > I assume you mean something as below? It raises an important point: uffd-wp must be handled accordingly. > > diff --git a/mm/memory.c b/mm/memory.c > index eef4e482c0c2..dbf1ba8ccfd6 100644 > --- a/mm/memory.c > +++ b/mm/memory.c > @@ -4317,6 +4317,10 @@ vm_fault_t do_swap_page(struct vm_fault *vmf) > add_mm_counter(vma->vm_mm, MM_SWAPENTS, -nr_pages); > pte = mk_pte(page, vma->vm_page_prot); > > + if (pte_swp_soft_dirty(vmf->orig_pte)) > + pte = pte_mksoft_dirty(pte); > + if (pte_swp_uffd_wp(vmf->orig_pte)) > + pte = pte_mkuffd_wp(pte); > /* > * Same logic as in do_wp_page(); however, optimize for pages that are > * certainly not shared either because we just allocated them without > @@ -4325,18 +4329,19 @@ 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) { > + if (vmf->flags & FAULT_FLAG_WRITE) { > + pte = pte_mkwrite(pte_mkdirty(pte), vma); > + vmf->flags &= ~FAULT_FLAG_WRITE; > + } else if ((!vma_soft_dirty_enabled(vma) || > pte_soft_dirty(pte)) > + && !userfaultfd_pte_wp(vma, pte)) { > + pte = pte_mkwrite(pte, vma); Even with FAULT_FLAG_WRITE we must respect uffd-wp and *not* do a pte_mkwrite(pte). So we have to catch and handle that earlier (I could have sworn we handle that somehow). Note that the existing pte = pte_mkuffd_wp(pte); Will fix that up because it does an implicit pte_wrprotect(). So maybe what would work is if ((vma->vm_flags & VM_WRITE) && !userfaultfd_pte_wp(vma, pte) && !vma_soft_dirty_enabled(vma)) { pte = pte_mkwrite(pte); /* Only set the PTE dirty on write fault. */ if (vmf->flags & FAULT_FLAG_WRITE) { pte = pte_mkdirty(pte); vmf->flags &= ~FAULT_FLAG_WRITE; } } -- Cheers, David / dhildenb