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[2003:d8:2f02:2900:f54f:bad7:c5f4:9404]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-43f206332d9sm207208725e9.13.2025.04.15.04.59.01 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 15 Apr 2025 04:59:01 -0700 (PDT) Message-ID: <1d6d7842-1700-40d2-9d5b-e044fbc242de@redhat.com> Date: Tue, 15 Apr 2025 13:59:00 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mempolicy: Optimize queue_folios_pte_range by PTE batching To: Dev Jain , akpm@linux-foundation.org Cc: ryan.roberts@arm.com, willy@infradead.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, hughd@google.com, vishal.moola@gmail.com, yang@os.amperecomputing.com, ziy@nvidia.com References: <20250411081301.8533-1-dev.jain@arm.com> <09c77ab5-65fc-4bca-a7e5-2b11bba9330d@redhat.com> <9ed4c113-37eb-4e3d-98a1-f46f786aaea9@arm.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: <9ed4c113-37eb-4e3d-98a1-f46f786aaea9@arm.com> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: kZqkiQoml7HzYzphi3RnOij6gWgGCRtxMeD8TKhSsuU_1744718343 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-Queue-Id: 2692720002 X-Rspamd-Server: rspam04 X-Stat-Signature: 9itjo8cb7k43d1umxq6qbjjnmptzrzst X-HE-Tag: 1744718345-525768 X-HE-Meta: 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 DY49odtF 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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 15.04.25 13:47, Dev Jain wrote: > > > On 15/04/25 3:47 pm, David Hildenbrand wrote: >> On 11.04.25 10:13, Dev Jain wrote: >>> After the check for queue_folio_required(), the code only cares about the >>> folio in the for loop, i.e the PTEs are redundant. Therefore, optimize >>> this >>> loop by skipping over a PTE batch mapping the same folio. >>> >>> Signed-off-by: Dev Jain >>> --- >>> Unfortunately I have only build tested this since my test environment is >>> broken. >>> >>>   mm/mempolicy.c | 12 +++++++++++- >>>   1 file changed, 11 insertions(+), 1 deletion(-) >>> >>> diff --git a/mm/mempolicy.c b/mm/mempolicy.c >>> index b28a1e6ae096..b019524da8a2 100644 >>> --- a/mm/mempolicy.c >>> +++ b/mm/mempolicy.c >>> @@ -573,6 +573,9 @@ static int queue_folios_pte_range(pmd_t *pmd, >>> unsigned long addr, >>>       pte_t *pte, *mapped_pte; >>>       pte_t ptent; >>>       spinlock_t *ptl; >>> +    int max_nr; >>> +    const fpb_t fpb_flags = FPB_IGNORE_DIRTY | FPB_IGNORE_SOFT_DIRTY; >>> +    int nr = 1; >> >> Try sticking to reverse xmas tree, please. (not completely the case >> here, but fpb_flags can easily be moved all he way to the top) > > I thought that the initializations were to be kept at the bottom. Not that I am aware of. > Asking for future patches, should I put all declarations in reverse-xmas > fashion (even those which I don't intend to touch w.r.t the patch > logic), or do I do that for only my additions? We try to stay as close to reverse-xmas tree as possible. It's not always possible (e.g., dependent assignments), but fpb_flags in this case here can easily go all the way to the top. ... > >> >> >       ptl = pmd_trans_huge_lock(pmd, vma);>       if (ptl) { >>> @@ -586,7 +589,8 @@ static int queue_folios_pte_range(pmd_t *pmd, >>> unsigned long addr, >>>           walk->action = ACTION_AGAIN; >>>           return 0; >>>       } >> > -    for (; addr != end; pte++, addr += PAGE_SIZE) {> +    for (; >> addr != end; pte += nr, addr += nr * PAGE_SIZE) { >>> +        nr = 1; >>>           ptent = ptep_get(pte); >>>           if (pte_none(ptent)) >>>               continue; >>> @@ -607,6 +611,11 @@ static int queue_folios_pte_range(pmd_t *pmd, >>> unsigned long addr, >>>           if (!queue_folio_required(folio, qp)) >>>               continue; >>>           if (folio_test_large(folio)) { >>> +            max_nr = (end - addr) >> PAGE_SHIFT; >>> +            if (max_nr != 1) >>> +                nr = folio_pte_batch(folio, addr, pte, ptent, >>> +                             max_nr, fpb_flags, >>> +                             NULL, NULL, NULL); >> >> We should probably do that immediately after we verified that >> vm_normal_folio() have us something reasonable. > > But shouldn't we keep the small folio case separate to avoid the > overhead of folio_pte_batch()? Yes, just do something like if (folio_test_large(folio) && end - addr > 1) nr = folio_pte_batch(folio, addr, pte, ptent, end - addr, max_nr, fpb_flags, ...); before the folio_test_reserved(). Then you'd also skip the all ptes if !queue_folio_required. > >> >>>               /* >>>                * A large folio can only be isolated from LRU once, >>>                * but may be mapped by many PTEs (and Copy-On-Write may >>> @@ -633,6 +642,7 @@ static int queue_folios_pte_range(pmd_t *pmd, >>> unsigned long addr, >>>               qp->nr_failed++; >>>               if (strictly_unmovable(flags)) >>>                   break; >>> +            qp->nr_failed += nr - 1; >> >> Can't we do qp->nr_failed += nr; above? > > I did not dive deep into the significance of nr_failed, but I did that > to keep the code, before and after the change, equivalent: And I question exactly that. If we hit strictly_unmovable(flags), we end up returning "-EIO" from queue_folios_pte_range(). And staring at queue_pages_range(), we ignore nr_failed if walk_page_range() returned an error. So looks like we can just add everything in one shot, independent of strictly_unmovable()? -- Cheers, David / dhildenb