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[2003:cb:c74b:d000:3a9:de5c:9ae6:ccb3]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-38246b7db13sm6799690f8f.91.2024.11.19.08.52.06 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 19 Nov 2024 08:52:07 -0800 (PST) Message-ID: Date: Tue, 19 Nov 2024 17:52:06 +0100 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 mm-unstable v2 1/3] mm/contig_alloc: support __GFP_COMP From: David Hildenbrand To: Zi Yan Cc: Yu Zhao , Andrew Morton , Muchun Song , "Matthew Wilcox (Oracle)" , linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20240814035451.773331-1-yuzhao@google.com> <20240814035451.773331-2-yuzhao@google.com> <402ff3e5-4fca-4452-97ba-5b1ec4a6eeb1@redhat.com> <00721702-78FF-4690-8EAA-31C367FA9FC0@nvidia.com> <1a77f16b-d637-40b4-bf47-a8236729a0ca@redhat.com> <57A6BDB9-119B-4C1F-8715-2584046A5EA8@nvidia.com> <833078e4-3661-451a-bc11-3cb60a302946@redhat.com> 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: <833078e4-3661-451a-bc11-3cb60a302946@redhat.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 19.11.24 17:49, David Hildenbrand wrote: > On 19.11.24 17:41, Zi Yan wrote: >> On 19 Nov 2024, at 11:31, David Hildenbrand wrote: >> >>> On 19.11.24 17:12, Zi Yan wrote: >>>> On 19 Nov 2024, at 10:29, David Hildenbrand wrote: >>>> >>>>>> +/* Split a multi-block free page into its individual pageblocks. */ >>>>>> +static void split_large_buddy(struct zone *zone, struct page *page, >>>>>> + unsigned long pfn, int order, fpi_t fpi) >>>>>> +{ >>>>>> + unsigned long end = pfn + (1 << 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); >>>>>> + >>>>>> + __free_one_page(page, pfn, zone, order, mt, fpi); >>>>>> + pfn += 1 << order; >>>>>> + page = pfn_to_page(pfn); >>>>>> + } >>>>>> +} >>>>> >>>>> Hi, >>>>> >>>>> stumbling over this while digging through the code .... >>>>> >>>>>> + >>>>>> static void free_one_page(struct zone *zone, struct page *page, >>>>>> unsigned long pfn, unsigned int order, >>>>>> fpi_t fpi_flags) >>>>>> { >>>>>> unsigned long flags; >>>>>> - int migratetype; >>>>>> spin_lock_irqsave(&zone->lock, flags); >>>>>> - migratetype = get_pfnblock_migratetype(page, pfn); >>>>>> - __free_one_page(page, pfn, zone, order, migratetype, fpi_flags); >>>>> >>>>> This change is rather undesired: >>>>> >>>>> via __free_pages_core()->__free_pages_ok() we can easily end up here with order=MAX_PAGE_ORDER. >>>> >>>> Do you have a concrete example? PMD THP on x86_64 is pageblock_order. >>>> We do not have PMD level mTHP yet. Any other possible source? >>>> >>>>> >>>>> What your new code will do is split this perfectly reasonable MAX_PAGE_ORDER chunk via split_large_buddy() into pageblock-sized chunks, and let the buddy merging logic undo our unnecessary splitting. >>>>> >>>>> Is there a way to avoid this and just process the whole MAX_PAGE_ORDER chunk like we used to? >>>> >>>> Probably split_large_buddy() can check the migratetypes of the to-be-freed >>>> page, if order > pageblock_order. If all migratetypes are the same, the page >>>> can be freed at MAX_PAGE_ORDER, otherwise pageblock_order. >>> >>> Thinking about this: why do we care about the migratetype? >>> >>> We only have to fallback to pageblocks if any pageblock is "MIGRATE_ISOLATE" (and maybe MIGRATE_CMA), but not all. Otherwise, we can just ignore the migratetype (or rather overwrite it) >> >> There are VM_WARN_ONCEs around *_free_list() operations to make sure >> page migratetype matches the migratetype of the list it is on. Ignoring >> migratetype would trigger these WARNs. Overwriting it would work but >> free page migratetype accounting needs to be taken care of. >> >> An implicit reason is that __free_one_page() does not support >MAX_PAGE_ORDER >> and gigantic hugetlb folios are freed via free_one_page(), where >> split_large_buddy() is used to work around the limitation. > > Yes, I saw that change. But that can be easily identified cased by > unlikely(order > MAX_PAGE_ORDER) to handle that rare case in a special way. > > > > For the two memory init cases you mentioned in the other email, > maybe a new >> fpi flag to make free_one_page() use __free_one_page() for them, >> since migratetypes should be the same across MAX_PAGE_ORDER range there, right? > > In the context of alloc_frozen_range()/free_frozen_range() I want to > free MAX_PAGE_ORDER chunks when possible, and not have some odd logic in > the freeing path undo some of that effort. Adding a pointer to that discussion: https://lkml.kernel.org/r/ZzZdnuZBf-xgiwD2@casper.infradead.org -- Cheers, David / dhildenb