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[2003:cb:c70f:6900:6c56:80f8:c14:6d2a]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3a073c8cc74sm3339530f8f.11.2025.04.25.13.12.50 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 25 Apr 2025 13:12:51 -0700 (PDT) Message-ID: <8fd728cf-bc54-433d-8701-234a67933a97@redhat.com> Date: Fri, 25 Apr 2025 22:12:49 +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 v4 7/7] mm/mm_init: Use for_each_valid_pfn() in init_unavailable_range() To: David Woodhouse , Mike Rapoport Cc: Andrew Morton , "Sauerwein, David" , Anshuman Khandual , Ard Biesheuvel , Catalin Marinas , Marc Zyngier , Mark Rutland , Mike Rapoport , Will Deacon , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Ruihan Li References: <20250423133821.789413-1-dwmw2@infradead.org> <20250423133821.789413-8-dwmw2@infradead.org> <91CA8854-2E86-4AF3-BAD0-8C47833F59D4@infradead.org> 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: <91CA8854-2E86-4AF3-BAD0-8C47833F59D4@infradead.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 25.04.25 21:08, David Woodhouse wrote: > On 25 April 2025 17:17:25 BST, David Hildenbrand wrote: >> On 23.04.25 15:33, David Woodhouse wrote: >>> From: David Woodhouse >>> >>> Currently, memmap_init initializes pfn_hole with 0 instead of >>> ARCH_PFN_OFFSET. Then init_unavailable_range will start iterating each >>> page from the page at address zero to the first available page, but it >>> won't do anything for pages below ARCH_PFN_OFFSET because pfn_valid >>> won't pass. >>> >>> If ARCH_PFN_OFFSET is very large (e.g., something like 2^64-2GiB if the >>> kernel is used as a library and loaded at a very high address), the >>> pointless iteration for pages below ARCH_PFN_OFFSET will take a very >>> long time, and the kernel will look stuck at boot time. >>> >>> Use for_each_valid_pfn() to skip the pointless iterations. >>> >>> Reported-by: Ruihan Li >>> Suggested-by: Mike Rapoport >>> Signed-off-by: David Woodhouse >>> Reviewed-by: Mike Rapoport (Microsoft) >>> Tested-by: Ruihan Li >>> --- >>> mm/mm_init.c | 6 +----- >>> 1 file changed, 1 insertion(+), 5 deletions(-) >>> >>> diff --git a/mm/mm_init.c b/mm/mm_init.c >>> index 41884f2155c4..0d1a4546825c 100644 >>> --- a/mm/mm_init.c >>> +++ b/mm/mm_init.c >>> @@ -845,11 +845,7 @@ static void __init init_unavailable_range(unsigned long spfn, >>> unsigned long pfn; >>> u64 pgcnt = 0; >>> - for (pfn = spfn; pfn < epfn; pfn++) { >>> - if (!pfn_valid(pageblock_start_pfn(pfn))) { >>> - pfn = pageblock_end_pfn(pfn) - 1; >>> - continue; >>> - } >> >> So, if the first pfn in a pageblock is not valid, we skip the whole pageblock ... >> >>> + for_each_valid_pfn(pfn, spfn, epfn) { >>> __init_single_page(pfn_to_page(pfn), pfn, zone, node); >>> __SetPageReserved(pfn_to_page(pfn)); >>> pgcnt++; >> >> but here, we would process further pfns inside such a pageblock? >> > > Is it not the case that either *all*, or *none*, of the PFNs within a given pageblock will be valid? Hmm, good point. I was thinking about sub-sections, but all early sections are fully valid. (Also, at least on x86, the subsection size should match the pageblock size; might not be the case on other architectures, like arm64 with 64K base pages ...) > > I assumed that was *why* it had that skip, as an attempt at the kind of optimisation that for_each_valid_pfn() now gives us? But it's interesting in this code that we didn't optimize for "if the first pfn is valid, all the remaining ones are valid". We would still check each PFN. In any case, trying to figure out why Lorenzo ran into an issue ... if it's nit because of the pageblock, maybe something in for_each_valid_pfn with sparsemem is still shaky. -- Cheers, David / dhildenb