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[2003:cb:c71b:2c00:7bfb:29fe:9e6f:2e65]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4350159f6a4sm12209525e9.21.2024.12.09.13.35.25 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 09 Dec 2024 13:35:26 -0800 (PST) Message-ID: Date: Mon, 9 Dec 2024 22:35:25 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v1 1/2] mm/page_alloc: conditionally split > pageblock_order pages in free_one_page() and move_freepages_block_isolate() To: Zi Yan , Vlastimil Babka Cc: linux-kernel@vger.kernel.org, Johannes Weiner , linux-mm@kvack.org, Andrew Morton , Yu Zhao References: <20241206095951.98007-1-david@redhat.com> <20241206095951.98007-2-david@redhat.com> <37B7A92E-B58F-442D-8501-B07A507F0451@nvidia.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: <37B7A92E-B58F-442D-8501-B07A507F0451@nvidia.com> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: wT5G_9NqeVUa8y9uwhOfmdZ9dNj4xvHRvOoZAriOeEQ_1733780128 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Stat-Signature: nyseopa8hkmrgi99wfjc9dh4o9qhxh4x X-Rspamd-Queue-Id: 9A71B180015 X-Rspam-User: X-Rspamd-Server: rspam01 X-HE-Tag: 1733780128-840428 X-HE-Meta: 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 iWtDcWRz 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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 09.12.24 20:23, Zi Yan wrote: > On 9 Dec 2024, at 14:01, Vlastimil Babka wrote: > >> On 12/6/24 10:59, David Hildenbrand wrote: >>> Let's special-case for the common scenarios that: >>> >>> (a) We are freeing pages <= pageblock_order >>> (b) We are freeing a page <= MAX_PAGE_ORDER and all pageblocks match >>> (especially, no mixture of isolated and non-isolated pageblocks) >> >> Well in many of those cases we could also just adjust the pageblocks... But >> perhaps they indeed shouldn't differ in the first place, unless there's an >> isolation attempt. >> >>> When we encounter a > MAX_PAGE_ORDER page, it can only come from >>> alloc_contig_range(), and we can process MAX_PAGE_ORDER chunks. >>> >>> When we encounter a >pageblock_order <= MAX_PAGE_ORDER page, >>> check whether all pageblocks match, and if so (common case), don't >>> split them up just for the buddy to merge them back. >>> >>> This makes sure that when we free MAX_PAGE_ORDER chunks to the buddy, >>> for example during system startups, memory onlining, or when isolating >>> consecutive pageblocks via alloc_contig_range()/memory offlining, that >>> we don't unnecessarily split up what we'll immediately merge again, >>> because the migratetypes match. >>> >>> Rename split_large_buddy() to __free_one_page_maybe_split(), to make it >>> clearer what's happening, and handle in it only natural buddy orders, >>> not the alloc_contig_range(__GFP_COMP) special case: handle that in >>> free_one_page() only. >>> >>> Signed-off-by: David Hildenbrand >> >> Acked-by: Vlastimil Babka > >> Hm but noticed something: >> >>> +static void __free_one_page_maybe_split(struct zone *zone, struct page *page, >>> + unsigned long pfn, int order, fpi_t fpi_flags) >>> +{ >>> + const unsigned long end_pfn = pfn + (1 << order); >>> + int mt = get_pfnblock_migratetype(page, pfn); >>> + >>> + VM_WARN_ON_ONCE(order > MAX_PAGE_ORDER); >>> VM_WARN_ON_ONCE(!IS_ALIGNED(pfn, 1 << order)); >>> /* Caller removed page from freelist, buddy info cleared! */ >>> VM_WARN_ON_ONCE(PageBuddy(page)); >>> >>> - if (order > pageblock_order) >>> - order = pageblock_order; >>> - >>> - while (pfn != end) { >>> - int mt = get_pfnblock_migratetype(page, pfn); >>> + /* >>> + * With CONFIG_MEMORY_ISOLATION, we might be freeing MAX_ORDER_NR_PAGES >>> + * pages that cover pageblocks with different migratetypes; for example >>> + * only some migratetypes might be MIGRATE_ISOLATE. In that (unlikely) >>> + * case, fallback to freeing individual pageblocks so they get put >>> + * onto the right lists. >>> + */ >>> + if (!IS_ENABLED(CONFIG_MEMORY_ISOLATION) || >>> + likely(order <= pageblock_order) || >>> + pfnblock_migratetype_equal(pfn + pageblock_nr_pages, end_pfn, mt)) { >>> + __free_one_page(page, pfn, zone, order, mt, fpi_flags); >>> + return; >>> + } >>> >>> - __free_one_page(page, pfn, zone, order, mt, fpi); >>> - pfn += 1 << order; >>> + while (pfn != end_pfn) { >>> + mt = get_pfnblock_migratetype(page, pfn); >>> + __free_one_page(page, pfn, zone, pageblock_order, mt, fpi_flags); >>> + pfn += pageblock_nr_pages; >>> page = pfn_to_page(pfn); >> >> This predates your patch, but seems potentially dangerous to attempt >> pfn_to_page(end_pfn) with SPARSEMEM and no vmemmap and the end_pfn perhaps >> being just outside of the valid range? Should we change that? >> >> But seems this code was initially introduced as part of Johannes' >> migratetype hygiene series. > > It starts as split_free_page() from commit b2c9e2fbba32 ("mm: make > alloc_contig_range work at pageblock granularity”), but harmless since > it is only used to split a buddy page. Then commit fd919a85cd55 ("mm: > page_isolation: prepare for hygienic freelists") refactored it, which > should be fine, since it is still used for the same purpose in page > isolation. Then commit e98337d11bbd ("mm/contig_alloc: support __GFP_COMP") > used it for gigantic hugetlb. > > For SPARSEMEM && !SPARSEMEM_VMEMMAP, PFNs are contiguous, vmemmap might not > be. The code above using pfn in the loop might be fine. And since order > is provided, unless the caller is providing a falsely large order, pfn > should be valid. Or am I missing anything? I think the question is, what happens when we call pfn_to_page() on a PFN that falls into a memory section that is either offline, doesn't have a memmap, or does not exist. With CONFIG_SPARSEMEM, we do a struct mem_section *__sec = __pfn_to_section(__pfn) __section_mem_map_addr(__sec) + __pfn; __pfn_to_section() can return NULL, in which case __section_mem_map_addr() would dereference NULL. I assume it ould happen in corner cases, if we'd exceed NR_SECTION_ROOTS. (IOW, large memory, and we free a page that is at the very end of physical memory). Likely, we should do the pfn_to_page() before the __free_one_page() call. -- Cheers, David / dhildenb