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[2003:cb:c708:e100:4f41:ff29:a59f:8c7a]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-38a8e37e36asm5199428f8f.5.2025.01.10.11.32.52 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 10 Jan 2025 11:32:54 -0800 (PST) Message-ID: <542e2241-33ff-4ebd-9ee7-d95413d2ad1e@redhat.com> Date: Fri, 10 Jan 2025 20:32:52 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v1 6/6] mm/hugetlb: use folio->lru int demote_free_hugetlb_folios() To: Matthew Wilcox Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, Andrew Morton , Muchun Song References: <20250110182149.746551-1-david@redhat.com> <20250110182149.746551-7-david@redhat.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: X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: SNV2xm-yp4nREkXoHmperRAmKN9Wjm0TcZDnGmc4gEc_1736537576 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: E59AD1C001A X-Rspamd-Server: rspam12 X-Stat-Signature: 691y7okxnzijfrmxiumho1ne64ocz8a9 X-Rspam-User: X-HE-Tag: 1736537580-627425 X-HE-Meta: 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 1DcfzY1J 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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 10.01.25 19:59, Matthew Wilcox wrote: > On Fri, Jan 10, 2025 at 07:21:49PM +0100, David Hildenbrand wrote: >> We are demoting hugetlb folios to smaller hugetlb folios; let's avoid >> messing with pages where avoidable. >> >> Signed-off-by: David Hildenbrand > > Good stuff. I have questions. > >> +++ b/mm/hugetlb.c >> @@ -3822,13 +3822,15 @@ static long demote_free_hugetlb_folios(struct hstate *src, struct hstate *dst, >> >> for (i = 0; i < pages_per_huge_page(src); i += pages_per_huge_page(dst)) { >> struct page *page = folio_page(folio, i); >> + struct folio *new_folio; > > I'm usually very against casting from page to folio, but I think it > might be the better option in this case ... > >> page->mapping = NULL; > > because then we could do new_folio->mapping = NULL. > > We're going to have to do serious changes to this function anyway to > convert from Ottawa to the New York interpretation, so the cast doesn't > give me the feeling of danger that it would elsewhere. Hm, that makes me wonder if we should do it even more similar like our other split function (__split_huge_page_tail)? diff --git a/mm/hugetlb.c b/mm/hugetlb.c index 60617eecb99dd..23fe5654f632c 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -3821,14 +3821,18 @@ static long demote_free_hugetlb_folios(struct hstate *src, struct hstate *dst, pgalloc_tag_split(folio, huge_page_order(src), huge_page_order(dst)); for (i = 0; i < pages_per_huge_page(src); i += pages_per_huge_page(dst)) { struct page *page = folio_page(folio, i); + /* Careful: see __split_huge_page_tail() */ + struct folio *new_folio = (struct folio *)page; - page->mapping = NULL; clear_compound_head(page); prep_compound_page(page, dst->order); - init_new_hugetlb_folio(dst, page_folio(page)); - list_add(&page->lru, &dst_list); + new_folio->mapping = NULL; + init_new_hugetlb_folio(dst, new_folio); + list_add(&new_folio->lru, &dst_list); } } I was even wondering if we should be using nth_page() instead of folio_page() -- similar to __split_huge_page_tail. If we'd add sanity checking in current code to folio_page() to verify that i falls inside the folio, the current code would blow up as we modify the folio using prep_compound_page(). -- Cheers, David / dhildenb