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(p200300d82f1a37002982b5f7a04e4cb4.dip0.t-ipconnect.de. [2003:d8:2f1a:3700:2982:b5f7:a04e:4cb4]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3a568b09148sm1547927f8f.58.2025.06.13.00.44.12 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 13 Jun 2025 00:44:13 -0700 (PDT) Message-ID: <51520205-07f5-45c2-b3e3-cf58a95d9fe6@redhat.com> Date: Fri, 13 Jun 2025 09:44:12 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 2/3] mm/huge_memory: don't mark refcounted folios special in vmf_insert_folio_pmd() To: Lorenzo Stoakes Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, nvdimm@lists.linux.dev, linux-cxl@vger.kernel.org, Andrew Morton , Alistair Popple , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Zi Yan , Baolin Wang , Nico Pache , Ryan Roberts , Dev Jain , Dan Williams , Oscar Salvador References: <20250611120654.545963-1-david@redhat.com> <20250611120654.545963-3-david@redhat.com> <434c6cfd-ba83-4d3c-8bde-736fcb8e9d91@lucifer.local> 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: <434c6cfd-ba83-4d3c-8bde-736fcb8e9d91@lucifer.local> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: DA8msjIG7Vm_vOr86oAMYB-znZPZ8OIBuGlxzlAoGWM_1749800655 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 298DC140003 X-Stat-Signature: jta8ydbjj996xs7w3n8htnupukpepxad X-Rspam-User: X-HE-Tag: 1749800657-173535 X-HE-Meta: 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 9UjI9lWS Gu0RGLGepJRmkJkVTcnZJp1pmYDreYbLvsR3SuBIXqZoRVD3ZtDBLVtcsEzqreh184M6BTWkV5OSxOXo+sUj0SyqP19nV5inswqrT624PRF8Ki4okBb30aVWJo+3RpZv6Z4+6 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 12.06.25 18:10, Lorenzo Stoakes wrote: > On Wed, Jun 11, 2025 at 02:06:53PM +0200, David Hildenbrand wrote: >> Marking PMDs that map a "normal" refcounted folios as special is >> against our rules documented for vm_normal_page(). >> >> Fortunately, there are not that many pmd_special() check that can be >> mislead, and most vm_normal_page_pmd()/vm_normal_folio_pmd() users that >> would get this wrong right now are rather harmless: e.g., none so far >> bases decisions whether to grab a folio reference on that decision. >> >> Well, and GUP-fast will fallback to GUP-slow. All in all, so far no big >> implications as it seems. >> >> Getting this right will get more important as we use >> folio_normal_page_pmd() in more places. >> >> Fix it by teaching insert_pfn_pmd() to properly handle folios and >> pfns -- moving refcount/mapcount/etc handling in there, renaming it to >> insert_pmd(), and distinguishing between both cases using a new simple >> "struct folio_or_pfn" structure. >> >> Use folio_mk_pmd() to create a pmd for a folio cleanly. >> >> Fixes: 6c88f72691f8 ("mm/huge_memory: add vmf_insert_folio_pmd()") >> Signed-off-by: David Hildenbrand > > Looks good to me, checked that the logic remains the same. Some micro > nits/thoughts below. So: > > Reviewed-by: Lorenzo Stoakes Thanks! > >> --- >> mm/huge_memory.c | 58 ++++++++++++++++++++++++++++++++---------------- >> 1 file changed, 39 insertions(+), 19 deletions(-) >> >> diff --git a/mm/huge_memory.c b/mm/huge_memory.c >> index 49b98082c5401..7e3e9028873e5 100644 >> --- a/mm/huge_memory.c >> +++ b/mm/huge_memory.c >> @@ -1372,9 +1372,17 @@ vm_fault_t do_huge_pmd_anonymous_page(struct vm_fault *vmf) >> return __do_huge_pmd_anonymous_page(vmf); >> } >> >> -static int insert_pfn_pmd(struct vm_area_struct *vma, unsigned long addr, >> - pmd_t *pmd, pfn_t pfn, pgprot_t prot, bool write, >> - pgtable_t pgtable) >> +struct folio_or_pfn { >> + union { >> + struct folio *folio; >> + pfn_t pfn; >> + }; >> + bool is_folio; >> +}; > > Interesting... I guess a memdesc world will make this easy... maybe? :) > > But this is a neat way of passing this. > > Another mega nit is mayyybe we could have a macro for making these like: > > > #define DECLARE_FOP_PFN(name_, pfn_) \ > struct folio_or_pfn name_ { \ > .pfn = pfn_, \ > .is_folio = false, \ > } > > #define DECLARE_FOP_FOLIO(name_, folio_) \ > struct folio_or_pfn name_ { \ > .folio = folio_, \ > .is_folio = true, \ > } > > But yeah maybe overkill for this small usage in this file. Yeah. I suspect at some point we will convert this into a folio+idx ("page") or "pfn" approach, at which point we could also use this for ordinary insert_pfn(). (hopefully, then we can also do pfn_t -> unsigned long) So let's defer adding that for now. > >> + >> +static int insert_pmd(struct vm_area_struct *vma, unsigned long addr, >> + pmd_t *pmd, struct folio_or_pfn fop, pgprot_t prot, >> + bool write, pgtable_t pgtable) >> { >> struct mm_struct *mm = vma->vm_mm; >> pmd_t entry; >> @@ -1382,8 +1390,11 @@ static int insert_pfn_pmd(struct vm_area_struct *vma, unsigned long addr, >> lockdep_assert_held(pmd_lockptr(mm, pmd)); >> >> if (!pmd_none(*pmd)) { >> + const unsigned long pfn = fop.is_folio ? folio_pfn(fop.folio) : >> + pfn_t_to_pfn(fop.pfn); >> + >> if (write) { >> - if (pmd_pfn(*pmd) != pfn_t_to_pfn(pfn)) { >> + if (pmd_pfn(*pmd) != pfn) { >> WARN_ON_ONCE(!is_huge_zero_pmd(*pmd)); >> return -EEXIST; >> } >> @@ -1396,11 +1407,19 @@ static int insert_pfn_pmd(struct vm_area_struct *vma, unsigned long addr, >> return -EEXIST; >> } >> >> - entry = pmd_mkhuge(pfn_t_pmd(pfn, prot)); >> - if (pfn_t_devmap(pfn)) >> - entry = pmd_mkdevmap(entry); >> - else >> - entry = pmd_mkspecial(entry); >> + if (fop.is_folio) { >> + entry = folio_mk_pmd(fop.folio, vma->vm_page_prot); >> + >> + folio_get(fop.folio); >> + folio_add_file_rmap_pmd(fop.folio, &fop.folio->page, vma); >> + add_mm_counter(mm, mm_counter_file(fop.folio), HPAGE_PMD_NR); >> + } else { >> + entry = pmd_mkhuge(pfn_t_pmd(fop.pfn, prot)); > > Mega micro annoying nit - in above branch you have a newline after entry =, here > you don't. Maybe should add here also? Well, it's combining all the "entry" setup in one block. But I don't particularly care, so I'll just do it :) -- Cheers, David / dhildenb