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[2003:cb:c726:6800:7ddf:5fc:2ee5:f08a]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-39eae979663sm1359590f8f.51.2025.04.11.01.42.09 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 11 Apr 2025 01:42:10 -0700 (PDT) Message-ID: <6b532646-041f-4077-b09f-ff6d43aa4a81@redhat.com> Date: Fri, 11 Apr 2025 10:42:09 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH] mm: huge_memory: add folio_mark_accessed() when zapping file THP To: Baolin Wang , Barry Song <21cnbao@gmail.com>, Zi Yan Cc: akpm@linux-foundation.org, willy@infradead.org, ryan.roberts@arm.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <34bab7a60930472377afbfeefe05b980d0512aa4.1744118089.git.baolin.wang@linux.alibaba.com> <5c52b67a-8e7e-4dd7-9127-96944715d883@linux.alibaba.com> <1E123113-7A0B-4D3A-AC7A-01767D7BF2D8@nvidia.com> <247fca57-8280-41a6-85b0-03a32ea08210@linux.alibaba.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: <247fca57-8280-41a6-85b0-03a32ea08210@linux.alibaba.com> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: w-oJLD8BPHIEpVHF4IjITI3wQ9X1gtozzK2XpLmKiqM_1744360931 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-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 6A1FD140006 X-Stat-Signature: hq8tchtbaye93sqfi1k17ih5mfx85x3y X-HE-Tag: 1744360934-359482 X-HE-Meta: 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 Aah/slSU 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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 11.04.25 03:20, Baolin Wang wrote: > > > On 2025/4/11 05:56, Barry Song wrote: >> On Fri, Apr 11, 2025 at 3:13 AM Zi Yan wrote: >>> >>> On 10 Apr 2025, at 6:29, Barry Song wrote: >>> >>>> On Thu, Apr 10, 2025 at 9:05 PM Baolin Wang >>>> wrote: >>>>> >>>>> >>>>> >>>>> On 2025/4/10 16:14, Barry Song wrote: >>>>>> On Wed, Apr 9, 2025 at 1:16 AM Baolin Wang >>>>>> wrote: >>>>>>> >>>>>>> When investigating performance issues during file folio unmap, I noticed some >>>>>>> behavioral differences in handling non-PMD-sized folios and PMD-sized folios. >>>>>>> For non-PMD-sized file folios, it will call folio_mark_accessed() to mark the >>>>>>> folio as having seen activity, but this is not done for PMD-sized folios. >>>>>>> >>>>>>> This might not cause obvious issues, but a potential problem could be that, >>>>>>> it might lead to more frequent refaults of PMD-sized file folios under memory >>>>>>> pressure. Therefore, I am unsure whether the folio_mark_accessed() should be >>>>>>> added for PMD-sized file folios? >>>>>>> >>>>>>> Signed-off-by: Baolin Wang >>>>>>> --- >>>>>>> mm/huge_memory.c | 4 ++++ >>>>>>> 1 file changed, 4 insertions(+) >>>>>>> >>>>>>> diff --git a/mm/huge_memory.c b/mm/huge_memory.c >>>>>>> index 6ac6d468af0d..b3ade7ac5bbf 100644 >>>>>>> --- a/mm/huge_memory.c >>>>>>> +++ b/mm/huge_memory.c >>>>>>> @@ -2262,6 +2262,10 @@ int zap_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma, >>>>>>> zap_deposited_table(tlb->mm, pmd); >>>>>>> add_mm_counter(tlb->mm, mm_counter_file(folio), >>>>>>> -HPAGE_PMD_NR); >>>>>>> + >>>>>>> + if (flush_needed && pmd_young(orig_pmd) && >>>>>>> + likely(vma_has_recency(vma))) >>>>>>> + folio_mark_accessed(folio); >>>>>> >>>>>> Acked-by: Barry Song >>>>> >>>>> Thanks. >>>>> >>>>>> I also came across an interesting observation: on a memory-limited system, >>>>>> demoting unmapped file folios in the LRU—specifically when their mapcount >>>>>> drops from 1 to 0—can actually improve performance. >>>>> >>>>> These file folios are used only once? Can folio_set_dropbehind() be used >>>>> to optimize it, which can avoid the LRU activity movement in >>>>> folio_mark_accessed()? >>>> >>>> For instance, when a process, such as a game, just exits, it can be expected >>>> that it won't be used again in the near future. As a result, demoting >>>> its previously >>>> unmapped file pages can improve performance. >>> >>> Is it possible to mark the dying VMAs either VM_SEQ_READ or VM_RAND_READ >>> so that folio_mark_accessed() will be skipped? Or a new vm_flag? >>> Will it work? >> >> Actually took a more aggressive approach and observed good performance >> improvements on phones. After zap_pte_range() called remove_rmap(), >> the following logic was added: >> >> if (file_folio && !folio_mapped()) >> deactivate_file_folio(); >> >> This helps file folios from exiting processes get reclaimed more quickly >> during the MGLRU's min generation scan while the folios are probably >> in max gen. >> >> I'm not entirely sure if this is universally applicable or worth submitting as >> a patch. > > IMHO, I'm afraid this is not universally applicable. Although these file > folios have been unmapped, it's not certain that they won't be accessed > again. These file folios might be remapped and accessed again soon, or > accessed through read()/write() operations using a file descriptor. > > I agree with Zi's suggestion. Using some kind of madvise() hint to mark > these file folios as those that won't be accessed after being unmapped, > seems can work? Is that similar to MADV_COLD before unmap? -- Cheers, David / dhildenb