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[2003:d8:2f1b:b800:6fdb:1af2:4fbd:1fdf]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3a4f00a017esm20388061f8f.89.2025.06.04.01.12.01 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 04 Jun 2025 01:12:02 -0700 (PDT) Message-ID: <5023a912-1ee9-4082-8656-56e004623367@redhat.com> Date: Wed, 4 Jun 2025 10:12:00 +0200 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 v2] gup: optimize longterm pin_user_pages() for large folio To: lizhe.67@bytedance.com, akpm@linux-foundation.org, jgg@ziepe.ca, jhubbard@nvidia.com, peterx@redhat.com Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, dev.jain@arm.com, muchun.song@linux.dev References: <20250604031536.9053-1-lizhe.67@bytedance.com> From: David Hildenbrand Content-Language: en-US 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: <20250604031536.9053-1-lizhe.67@bytedance.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 04.06.25 05:15, lizhe.67@bytedance.com wrote: > From: Li Zhe > > In the current implementation of the longterm pin_user_pages() function, > we invoke the collect_longterm_unpinnable_folios() function. This function > iterates through the list to check whether each folio belongs to the > "longterm_unpinnabled" category. The folios in this list essentially > correspond to a contiguous region of user-space addresses, with each folio > representing a physical address in increments of PAGESIZE. If this > user-space address range is mapped with large folio, we can optimize the > performance of function pin_user_pages() by reducing the frequency of > memory accesses using READ_ONCE. This patch leverages this approach to > achieve performance improvements. > > The performance test results obtained through the gup_test tool from the > kernel source tree are as follows. We achieve an improvement of over 70% > for large folio with pagesize=2M. For normal page, we have only observed > a very slight degradation in performance. > > Without this patch: > > [root@localhost ~] ./gup_test -HL -m 8192 -n 512 > TAP version 13 > 1..1 > # PIN_LONGTERM_BENCHMARK: Time: get:13623 put:10799 us# > ok 1 ioctl status 0 > # Totals: pass:1 fail:0 xfail:0 xpass:0 skip:0 error:0 > [root@localhost ~]# ./gup_test -LT -m 8192 -n 512 > TAP version 13 > 1..1 > # PIN_LONGTERM_BENCHMARK: Time: get:129733 put:31753 us# > ok 1 ioctl status 0 > # Totals: pass:1 fail:0 xfail:0 xpass:0 skip:0 error:0 > > With this patch: > > [root@localhost ~] ./gup_test -HL -m 8192 -n 512 > TAP version 13 > 1..1 > # PIN_LONGTERM_BENCHMARK: Time: get:4075 put:10792 us# > ok 1 ioctl status 0 > # Totals: pass:1 fail:0 xfail:0 xpass:0 skip:0 error:0 > [root@localhost ~]# ./gup_test -LT -m 8192 -n 512 > TAP version 13 > 1..1 > # PIN_LONGTERM_BENCHMARK: Time: get:130727 put:31763 us# > ok 1 ioctl status 0 > # Totals: pass:1 fail:0 xfail:0 xpass:0 skip:0 error:0 > > Signed-off-by: Li Zhe > --- > Changelogs: > > v1->v2: > - Modify some unreliable code. > - Update performance test data. > > v1 patch: https://lore.kernel.org/all/20250530092351.32709-1-lizhe.67@bytedance.com/ > > mm/gup.c | 37 +++++++++++++++++++++++++++++-------- > 1 file changed, 29 insertions(+), 8 deletions(-) > > diff --git a/mm/gup.c b/mm/gup.c > index 84461d384ae2..57fd324473a1 100644 > --- a/mm/gup.c > +++ b/mm/gup.c > @@ -2317,6 +2317,31 @@ static void pofs_unpin(struct pages_or_folios *pofs) > unpin_user_pages(pofs->pages, pofs->nr_entries); > } > > +static struct folio *pofs_next_folio(struct folio *folio, > + struct pages_or_folios *pofs, long *index_ptr) > +{ > + long i = *index_ptr + 1; > + > + if (!pofs->has_folios) { && folio_test_large(folio) To avoid all that for small folios. > + unsigned long start_pfn = folio_pfn(folio);> + unsigned long end_pfn = start_pfn + folio_nr_pages(folio); I guess both could be const > +> + for (; i < pofs->nr_entries; i++) { > + unsigned long pfn = page_to_pfn(pofs->pages[i]); > + > + /* Is this page part of this folio? */ > + if ((pfn < start_pfn) || (pfn >= end_pfn)) No need for the inner () > + break; > + } > + } > + > + if (unlikely(i == pofs->nr_entries)) > + return NULL; > + *index_ptr = i;> + > + return pofs_get_folio(pofs, i); We're now doing two "pofs->has_folios" checks. Maybe the compiler is smart enough to figure that out. > +} > + > /*> * Returns the number of collected folios. Return value is always >= 0. > */ > @@ -2324,16 +2349,12 @@ static void collect_longterm_unpinnable_folios( > struct list_head *movable_folio_list, > struct pages_or_folios *pofs) > { > - struct folio *prev_folio = NULL; > bool drain_allow = true; > - unsigned long i; > - > - for (i = 0; i < pofs->nr_entries; i++) { > - struct folio *folio = pofs_get_folio(pofs, i); > + long i = 0; > + struct folio *folio; Please keep the reverse christmas tree where we have it. Why the change from "unsigned long" -> "long" ? > > - if (folio == prev_folio) > - continue; > - prev_folio = folio; > + for (folio = pofs_get_folio(pofs, 0); folio; > + folio = pofs_next_folio(folio, pofs, &i)) { Please indent as for (folio = pofs_get_folio(pofs, 0); folio; folio = pofs_next_folio(folio, pofs, &i)) { But the usage of "0" and "&i" is a bit suboptimal. for (folio = pofs_get_folio(pofs, i); folio; folio = pofs_next_folio(folio, pofs, &i)) { Might be better. -- Cheers, David / dhildenb