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(p200300d82f0df000eec92b8d4913f32a.dip0.t-ipconnect.de. [2003:d8:2f0d:f000:eec9:2b8d:4913:f32a]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3a4efe5b96fsm18005827f8f.8.2025.06.03.06.03.04 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 03 Jun 2025 06:03:05 -0700 (PDT) Message-ID: <54943dbb-45fe-4b69-a6a8-96381304a268@redhat.com> Date: Tue, 3 Jun 2025 15:03:03 +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 v7] mm: Add CONFIG_PAGE_BLOCK_ORDER to select page block order To: Juan Yescas , Andrew Morton , Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Zi Yan , linux-mm@kvack.org, linux-kernel@vger.kernel.org Cc: tjmercier@google.com, isaacmanjarres@google.com, kaleshsingh@google.com, masahiroy@kernel.org, Minchan Kim References: <20250521215807.1860663-1-jyescas@google.com> 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: <20250521215807.1860663-1-jyescas@google.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 21.05.25 23:57, Juan Yescas wrote: > Problem: On large page size configurations (16KiB, 64KiB), the CMA > alignment requirement (CMA_MIN_ALIGNMENT_BYTES) increases considerably, > and this causes the CMA reservations to be larger than necessary. > This means that system will have less available MIGRATE_UNMOVABLE and > MIGRATE_RECLAIMABLE page blocks since MIGRATE_CMA can't fallback to them. > > The CMA_MIN_ALIGNMENT_BYTES increases because it depends on > MAX_PAGE_ORDER which depends on ARCH_FORCE_MAX_ORDER. The value of > ARCH_FORCE_MAX_ORDER increases on 16k and 64k kernels. > > For example, in ARM, the CMA alignment requirement when: > > - CONFIG_ARCH_FORCE_MAX_ORDER default value is used > - CONFIG_TRANSPARENT_HUGEPAGE is set: > > PAGE_SIZE | MAX_PAGE_ORDER | pageblock_order | CMA_MIN_ALIGNMENT_BYTES > ----------------------------------------------------------------------- > 4KiB | 10 | 9 | 4KiB * (2 ^ 9) = 2MiB > 16Kib | 11 | 11 | 16KiB * (2 ^ 11) = 32MiB > 64KiB | 13 | 13 | 64KiB * (2 ^ 13) = 512MiB > > There are some extreme cases for the CMA alignment requirement when: > > - CONFIG_ARCH_FORCE_MAX_ORDER maximum value is set > - CONFIG_TRANSPARENT_HUGEPAGE is NOT set: > - CONFIG_HUGETLB_PAGE is NOT set > > PAGE_SIZE | MAX_PAGE_ORDER | pageblock_order | CMA_MIN_ALIGNMENT_BYTES > ------------------------------------------------------------------------ > 4KiB | 15 | 15 | 4KiB * (2 ^ 15) = 128MiB > 16Kib | 13 | 13 | 16KiB * (2 ^ 13) = 128MiB > 64KiB | 13 | 13 | 64KiB * (2 ^ 13) = 512MiB > > This affects the CMA reservations for the drivers. If a driver in a > 4KiB kernel needs 4MiB of CMA memory, in a 16KiB kernel, the minimal > reservation has to be 32MiB due to the alignment requirements: > > reserved-memory { > ... > cma_test_reserve: cma_test_reserve { > compatible = "shared-dma-pool"; > size = <0x0 0x400000>; /* 4 MiB */ > ... > }; > }; > > reserved-memory { > ... > cma_test_reserve: cma_test_reserve { > compatible = "shared-dma-pool"; > size = <0x0 0x2000000>; /* 32 MiB */ > ... > }; > }; > > Solution: Add a new config CONFIG_PAGE_BLOCK_ORDER that > allows to set the page block order in all the architectures. > The maximum page block order will be given by > ARCH_FORCE_MAX_ORDER. > > By default, CONFIG_PAGE_BLOCK_ORDER will have the same > value that ARCH_FORCE_MAX_ORDER. This will make sure that > current kernel configurations won't be affected by this > change. It is a opt-in change. > > This patch will allow to have the same CMA alignment > requirements for large page sizes (16KiB, 64KiB) as that > in 4kb kernels by setting a lower pageblock_order. > > Tests: > > - Verified that HugeTLB pages work when pageblock_order is 1, 7, 10 > on 4k and 16k kernels. > > - Verified that Transparent Huge Pages work when pageblock_order > is 1, 7, 10 on 4k and 16k kernels. > > - Verified that dma-buf heaps allocations work when pageblock_order > is 1, 7, 10 on 4k and 16k kernels. > > Benchmarks: > > The benchmarks compare 16kb kernels with pageblock_order 10 and 7. The > reason for the pageblock_order 7 is because this value makes the min > CMA alignment requirement the same as that in 4kb kernels (2MB). > > - Perform 100K dma-buf heaps (/dev/dma_heap/system) allocations of > SZ_8M, SZ_4M, SZ_2M, SZ_1M, SZ_64, SZ_8, SZ_4. Use simpleperf > (https://developer.android.com/ndk/guides/simpleperf) to measure > the # of instructions and page-faults on 16k kernels. > The benchmark was executed 10 times. The averages are below: > > # instructions | #page-faults > order 10 | order 7 | order 10 | order 7 > -------------------------------------------------------- > 13,891,765,770 | 11,425,777,314 | 220 | 217 > 14,456,293,487 | 12,660,819,302 | 224 | 219 > 13,924,261,018 | 13,243,970,736 | 217 | 221 > 13,910,886,504 | 13,845,519,630 | 217 | 221 > 14,388,071,190 | 13,498,583,098 | 223 | 224 > 13,656,442,167 | 12,915,831,681 | 216 | 218 > 13,300,268,343 | 12,930,484,776 | 222 | 218 > 13,625,470,223 | 14,234,092,777 | 219 | 218 > 13,508,964,965 | 13,432,689,094 | 225 | 219 > 13,368,950,667 | 13,683,587,37 | 219 | 225 > ------------------------------------------------------------------- > 13,803,137,433 | 13,131,974,268 | 220 | 220 Averages > > There were 4.85% #instructions when order was 7, in comparison > with order 10. > > 13,803,137,433 - 13,131,974,268 = -671,163,166 (-4.86%) > > The number of page faults in order 7 and 10 were the same. > > These results didn't show any significant regression when the > pageblock_order is set to 7 on 16kb kernels. > > - Run speedometer 3.1 (https://browserbench.org/Speedometer3.1/) 5 times > on the 16k kernels with pageblock_order 7 and 10. > > order 10 | order 7 | order 7 - order 10 | (order 7 - order 10) % > ------------------------------------------------------------------- > 15.8 | 16.4 | 0.6 | 3.80% > 16.4 | 16.2 | -0.2 | -1.22% > 16.6 | 16.3 | -0.3 | -1.81% > 16.8 | 16.3 | -0.5 | -2.98% > 16.6 | 16.8 | 0.2 | 1.20% > ------------------------------------------------------------------- > 16.44 16.4 -0.04 -0.24% Averages > > The results didn't show any significant regression when the > pageblock_order is set to 7 on 16kb kernels. > > Cc: Andrew Morton > Cc: Vlastimil Babka > Cc: Liam R. Howlett > Cc: Lorenzo Stoakes > Cc: David Hildenbrand > CC: Mike Rapoport > Cc: Zi Yan > Cc: Suren Baghdasaryan > Cc: Minchan Kim > Signed-off-by: Juan Yescas > Acked-by: Zi Yan > --- > Changes in v7: > - Update alignment calculation to 2MiB as per David's > observation. > - Update page block order calculation in mm/mm_init.c for > powerpc when CONFIG_HUGETLB_PAGE_SIZE_VARIABLE is set. > > Changes in v6: > - Applied the change provided by Zi Yan to fix > the Kconfig. The change consists in evaluating > to true or false in the if expression for range: > range 1 if . > > Changes in v5: > - Remove the ranges for CONFIG_PAGE_BLOCK_ORDER. The > ranges with config definitions don't work in Kconfig, > for example (range 1 MY_CONFIG). > - Add PAGE_BLOCK_ORDER_MANUAL config for the > page block order number. The default value was not > defined. > - Fix typos reported by Andrew. > - Test default configs in powerpc. > > Changes in v4: > - Set PAGE_BLOCK_ORDER in incluxe/linux/mmzone.h to > validate that MAX_PAGE_ORDER >= PAGE_BLOCK_ORDER at > compile time. > - This change fixes the warning in: > https://lore.kernel.org/oe-kbuild-all/202505091548.FuKO4b4v-lkp@intel.com/ > > Changes in v3: > - Rename ARCH_FORCE_PAGE_BLOCK_ORDER to PAGE_BLOCK_ORDER > as per Matthew's suggestion. > - Update comments in pageblock-flags.h for pageblock_order > value when THP or HugeTLB are not used. > > Changes in v2: > - Add Zi's Acked-by tag. > - Move ARCH_FORCE_PAGE_BLOCK_ORDER config to mm/Kconfig as > per Zi and Matthew suggestion so it is available to > all the architectures. > - Set ARCH_FORCE_PAGE_BLOCK_ORDER to 10 by default when > ARCH_FORCE_MAX_ORDER is not available. > > include/linux/mmzone.h | 16 ++++++++++++++++ > include/linux/pageblock-flags.h | 8 ++++---- > mm/Kconfig | 34 +++++++++++++++++++++++++++++++++ > mm/mm_init.c | 2 +- > 4 files changed, 55 insertions(+), 5 deletions(-) > > diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h > index 6ccec1bf2896..05610337bbb6 100644 > --- a/include/linux/mmzone.h > +++ b/include/linux/mmzone.h > @@ -37,6 +37,22 @@ > > #define NR_PAGE_ORDERS (MAX_PAGE_ORDER + 1) > > +/* Defines the order for the number of pages that have a migrate type. */ > +#ifndef CONFIG_PAGE_BLOCK_ORDER > +#define PAGE_BLOCK_ORDER MAX_PAGE_ORDER > +#else > +#define PAGE_BLOCK_ORDER CONFIG_PAGE_BLOCK_ORDER > +#endif /* CONFIG_PAGE_BLOCK_ORDER */ > + > +/* > + * The MAX_PAGE_ORDER, which defines the max order of pages to be allocated > + * by the buddy allocator, has to be larger or equal to the PAGE_BLOCK_ORDER, > + * which defines the order for the number of pages that can have a migrate type > + */ > +#if (PAGE_BLOCK_ORDER > MAX_PAGE_ORDER) > +#error MAX_PAGE_ORDER must be >= PAGE_BLOCK_ORDER > +#endif > + > /* > * PAGE_ALLOC_COSTLY_ORDER is the order at which allocations are deemed > * costly to service. That is between allocation orders which should > diff --git a/include/linux/pageblock-flags.h b/include/linux/pageblock-flags.h > index fc6b9c87cb0a..e73a4292ef02 100644 > --- a/include/linux/pageblock-flags.h > +++ b/include/linux/pageblock-flags.h > @@ -41,18 +41,18 @@ extern unsigned int pageblock_order; > * Huge pages are a constant size, but don't exceed the maximum allocation > * granularity. > */ > -#define pageblock_order MIN_T(unsigned int, HUGETLB_PAGE_ORDER, MAX_PAGE_ORDER) > +#define pageblock_order MIN_T(unsigned int, HUGETLB_PAGE_ORDER, PAGE_BLOCK_ORDER) > > #endif /* CONFIG_HUGETLB_PAGE_SIZE_VARIABLE */ > > #elif defined(CONFIG_TRANSPARENT_HUGEPAGE) > > -#define pageblock_order MIN_T(unsigned int, HPAGE_PMD_ORDER, MAX_PAGE_ORDER) > +#define pageblock_order MIN_T(unsigned int, HPAGE_PMD_ORDER, PAGE_BLOCK_ORDER) > > #else /* CONFIG_TRANSPARENT_HUGEPAGE */ > > -/* If huge pages are not used, group by MAX_ORDER_NR_PAGES */ > -#define pageblock_order MAX_PAGE_ORDER > +/* If huge pages are not used, group by PAGE_BLOCK_ORDER */ > +#define pageblock_order PAGE_BLOCK_ORDER > > #endif /* CONFIG_HUGETLB_PAGE */ > > diff --git a/mm/Kconfig b/mm/Kconfig > index e113f713b493..13a5c4f6e6b6 100644 > --- a/mm/Kconfig > +++ b/mm/Kconfig > @@ -989,6 +989,40 @@ config CMA_AREAS > > If unsure, leave the default value "8" in UMA and "20" in NUMA. > > +# > +# Select this config option from the architecture Kconfig, if available, to set > +# the max page order for physically contiguous allocations. > +# > +config ARCH_FORCE_MAX_ORDER > + int > + > +# > +# When ARCH_FORCE_MAX_ORDER is not defined, > +# the default page block order is MAX_PAGE_ORDER (10) as per > +# include/linux/mmzone.h. > +# > +config PAGE_BLOCK_ORDER > + int "Page Block Order" > + range 1 10 if ARCH_FORCE_MAX_ORDER = 0 > + default 10 if ARCH_FORCE_MAX_ORDER = 0 > + range 1 ARCH_FORCE_MAX_ORDER if ARCH_FORCE_MAX_ORDER != 0 > + default ARCH_FORCE_MAX_ORDER if ARCH_FORCE_MAX_ORDER != 0 > + help > + The page block order refers to the power of two number of pages that > + are physically contiguous and can have a migrate type associated to > + them. The maximum size of the page block order is limited by > + ARCH_FORCE_MAX_ORDER. > + > + This config allows overriding the default page block order when the > + page block order is required to be smaller than ARCH_FORCE_MAX_ORDER > + or MAX_PAGE_ORDER. > + > + Reducing pageblock order can negatively impact THP generation > + success rate. If your workloads uses THP heavily, please use this > + option with caution. > + > + Don't change if unsure. The semantics are now very confusing [1]. The default in x86-64 will be 10, so we'll have CONFIG_PAGE_BLOCK_ORDER=10 But then, we'll do this #define pageblock_order MIN_T(unsigned int, HPAGE_PMD_ORDER, PAGE_BLOCK_ORDER) So the actual pageblock order will be different than CONFIG_PAGE_BLOCK_ORDER. Confusing. Either CONFIG_PAGE_BLOCK_ORDER is misnamed (CONFIG_PAGE_BLOCK_ORDER_CEIL ? CONFIG_PAGE_BLOCK_ORDER_LIMIT ?), or the semantics should be changed. [1] https://gitlab.com/cki-project/kernel-ark/-/merge_requests/3928 -- Cheers, David / dhildenb