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[2003:cb:c707:4d00:6ac5:30d:1611:918f]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-43d830f5b41sm204350705e9.27.2025.04.01.06.04.43 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 01 Apr 2025 06:04:44 -0700 (PDT) Message-ID: Date: Tue, 1 Apr 2025 15:04:40 +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 2/2] mm: mincore: use folio_pte_batch() to batch process large folios To: Ryan Roberts , Baolin Wang , akpm@linux-foundation.org, hughd@google.com Cc: willy@infradead.org, 21cnbao@gmail.com, ziy@nvidia.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <7ad05bc9299de5d954fb21a2da57f46dd6ec59d0.1742960003.git.baolin.wang@linux.alibaba.com> <54886038-3707-4ea0-bd84-00a8f4a19a6a@arm.com> <145ec273-7223-45b8-a7f6-4e593a3cc8ee@arm.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: <145ec273-7223-45b8-a7f6-4e593a3cc8ee@arm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 01.04.25 12:45, Ryan Roberts wrote: > On 30/03/2025 15:57, Baolin Wang wrote: >> >> >> On 2025/3/27 22:08, Ryan Roberts wrote: >>> On 25/03/2025 23:38, Baolin Wang wrote: >>>> When I tested the mincore() syscall, I observed that it takes longer with >>>> 64K mTHP enabled on my Arm64 server. The reason is the mincore_pte_range() >>>> still checks each PTE individually, even when the PTEs are contiguous, >>>> which is not efficient. >>>> >>>> Thus we can use folio_pte_batch() to get the batch number of the present >>>> contiguous PTEs, which can improve the performance. I tested the mincore() >>>> syscall with 1G anonymous memory populated with 64K mTHP, and observed an >>>> obvious performance improvement: >>>> >>>> w/o patch        w/ patch        changes >>>> 6022us            1115us            +81% >>>> >>>> Moreover, I also tested mincore() with disabling mTHP/THP, and did not >>>> see any obvious regression. >>>> >>>> Signed-off-by: Baolin Wang >>>> --- >>>>   mm/mincore.c | 27 ++++++++++++++++++++++----- >>>>   1 file changed, 22 insertions(+), 5 deletions(-) >>>> >>>> diff --git a/mm/mincore.c b/mm/mincore.c >>>> index 832f29f46767..88be180b5550 100644 >>>> --- a/mm/mincore.c >>>> +++ b/mm/mincore.c >>>> @@ -21,6 +21,7 @@ >>>>     #include >>>>   #include "swap.h" >>>> +#include "internal.h" >>>>     static int mincore_hugetlb(pte_t *pte, unsigned long hmask, unsigned long >>>> addr, >>>>               unsigned long end, struct mm_walk *walk) >>>> @@ -105,6 +106,7 @@ static int mincore_pte_range(pmd_t *pmd, unsigned long >>>> addr, unsigned long end, >>>>       pte_t *ptep; >>>>       unsigned char *vec = walk->private; >>>>       int nr = (end - addr) >> PAGE_SHIFT; >>>> +    int step, i; >>>>         ptl = pmd_trans_huge_lock(pmd, vma); >>>>       if (ptl) { >>>> @@ -118,16 +120,31 @@ static int mincore_pte_range(pmd_t *pmd, unsigned long >>>> addr, unsigned long end, >>>>           walk->action = ACTION_AGAIN; >>>>           return 0; >>>>       } >>>> -    for (; addr != end; ptep++, addr += PAGE_SIZE) { >>>> +    for (; addr != end; ptep += step, addr += step * PAGE_SIZE) { >>>>           pte_t pte = ptep_get(ptep); >>>>   +        step = 1; >>>>           /* We need to do cache lookup too for pte markers */ >>>>           if (pte_none_mostly(pte)) >>>>               __mincore_unmapped_range(addr, addr + PAGE_SIZE, >>>>                            vma, vec); >>>> -        else if (pte_present(pte)) >>>> -            *vec = 1; >>>> -        else { /* pte is a swap entry */ >>>> +        else if (pte_present(pte)) { >>>> +            if (pte_batch_hint(ptep, pte) > 1) { >>>> +                struct folio *folio = vm_normal_folio(vma, addr, pte); >>>> + >>>> +                if (folio && folio_test_large(folio)) { >>>> +                    const fpb_t fpb_flags = FPB_IGNORE_DIRTY | >>>> +                                FPB_IGNORE_SOFT_DIRTY; >>>> +                    int max_nr = (end - addr) / PAGE_SIZE; >>>> + >>>> +                    step = folio_pte_batch(folio, addr, ptep, pte, >>>> +                            max_nr, fpb_flags, NULL, NULL, NULL); >>>> +                } >>>> +            } >>> >>> You could simplify to the following, I think, to avoid needing to grab the folio >>> and call folio_pte_batch(): >>> >>>             else if (pte_present(pte)) { >>>                 int max_nr = (end - addr) / PAGE_SIZE; >>>                 step = min(pte_batch_hint(ptep, pte), max_nr); >>>             } ... >>> >>> I expect the regression you are seeing here is all due to calling ptep_get() for >>> every pte in the contpte batch, which will cause 16 memory reads per pte (to >>> gather the access/dirty bits). For small folios its just 1 read per pte. >> >> Right. >> >>> pte_batch_hint() will skip forward in blocks of 16 so you now end up with the >>> same number as for the small folio case. You don't need all the fancy extras >>> that folio_pte_batch() gives you here. >> >> Sounds reasonable. Your suggestion looks simple, but my method can batch the >> whole large folio (such as large folios containing more than 16 contiguous PTEs) >> at once. > > Sure but folio_pte_batch() just implements that with another loop that calls > pte_batch_hint(), so it all amounts to the same thing. In fact there are some > extra checks in folio_pte_batch() that you don't need so it might be a bit slower. I don't enjoy open-coding the batching, especially if only cont-pte users will benefit from it. But I also don't enjoy the open-coded pte_batch_hint() :) But we really don't need the folio here, so I assume the short variant you (Ryan) suggest is alright to just avoid the ptep_get(). As Oscar says, these details might soon be hidden inside a new page table walker API (even though it will likely end up using folio_pte_batch() internally, TBD). -- Cheers, David / dhildenb