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[2003:d8:2f19:9c00:568:7df7:e1:293d]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-451f82871a4sm42742905e9.0.2025.06.06.10.37.39 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 06 Jun 2025 10:37:40 -0700 (PDT) Message-ID: <4c1d5033-0c90-4672-84a1-15978ced245d@redhat.com> Date: Fri, 6 Jun 2025 19:37:39 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC] mm: khugepaged: use largest enabled hugepage order for min_free_kbytes To: Usama Arif , Andrew Morton , linux-mm@kvack.org Cc: hannes@cmpxchg.org, shakeel.butt@linux.dev, riel@surriel.com, ziy@nvidia.com, baolin.wang@linux.alibaba.com, lorenzo.stoakes@oracle.com, Liam.Howlett@oracle.com, npache@redhat.com, ryan.roberts@arm.com, dev.jain@arm.com, hughd@google.com, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, kernel-team@meta.com References: <20250606143700.3256414-1-usamaarif642@gmail.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: <20250606143700.3256414-1-usamaarif642@gmail.com> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: pxPvlaqWPbiDINnq4r0suYsLVYxuddztzXHArvZ9g24_1749231461 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 83BD8120004 X-Stat-Signature: q7kyqp1pwzegiwnuihijuroopdupjr1d X-Rspam-User: X-HE-Tag: 1749231464-24012 X-HE-Meta: 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 DLWpCkx6 hsJblh5IOoQ6/HD3DaXYFtI4fwztQIxu3f9a6ny+rKALuDI0JhLOfBZNXGQX6yYKtlZ8O9cu4pELR5ji2KOC7omRlwTNJFRkeIGSmei6jiohLA3VAAerxr9S4tJ7FW5XdbdGxAaYXCkUDDB24YOqV3XQro+r91DIbNDiHpEb9etb256Cj61Z/VLTca+Vygmpj+gsLUgkusiebvgr/r6mxejRFg2b/e5Nj2+pxr8DbOatGsbgxaD3MoRdXuvhyM4ARAuX3OHGpmlqc+1AdR3d2gFW29dKd+FJ6TzqOWHVMXzb0m1r357YPk9ioAtg0+AXng27EABfez3xWVIi5ejZyrZu+k3OazIUpdavfH4gs5DLgbrnPYj86rBwdHUlGV0TojS/SGUSyqLiBp9N77eK/0M+6V42/BpaztDE6DNc1p4pcus1rjA4gJxyQAA5NicwI+N3VNeEhUa8ch+YNYKjILHyl6SU5JkFBuP6V 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 06.06.25 16:37, Usama Arif wrote: > On arm64 machines with 64K PAGE_SIZE, the min_free_kbytes and hence the > watermarks are evaluated to extremely high values, for e.g. a server with > 480G of memory, only 2M mTHP hugepage size set to madvise, with the rest > of the sizes set to never, the min, low and high watermarks evaluate to > 11.2G, 14G and 16.8G respectively. > In contrast for 4K PAGE_SIZE of the same machine, with only 2M THP hugepage > size set to madvise, the min, low and high watermarks evaluate to 86M, 566M > and 1G respectively. > This is because set_recommended_min_free_kbytes is designed for PMD > hugepages (pageblock_order = min(HPAGE_PMD_ORDER, PAGE_BLOCK_ORDER)). > Such high watermark values can cause performance and latency issues in > memory bound applications on arm servers that use 64K PAGE_SIZE, eventhough > most of them would never actually use a 512M PMD THP. > > Instead of using HPAGE_PMD_ORDER for pageblock_order use the highest large > folio order enabled in set_recommended_min_free_kbytes. > With this patch, when only 2M THP hugepage size is set to madvise for the > same machine with 64K page size, with the rest of the sizes set to never, > the min, low and high watermarks evaluate to 2.08G, 2.6G and 3.1G > respectively. When 512M THP hugepage size is set to madvise for the same > machine with 64K page size, the min, low and high watermarks evaluate to > 11.2G, 14G and 16.8G respectively, the same as without this patch. > > An alternative solution would be to change PAGE_BLOCK_ORDER by changing > ARCH_FORCE_MAX_ORDER to a lower value for ARM64_64K_PAGES. However, this > is not dynamic with hugepage size, will need different kernel builds for > different hugepage sizes and most users won't know that this needs to be > done as it can be difficult to detmermine that the performance and latency > issues are coming from the high watermark values. > > All watermark numbers are for zones of nodes that had the highest number > of pages, i.e. the value for min size for 4K is obtained using: > cat /proc/zoneinfo | grep -i min | awk '{print $2}' | sort -n | tail -n 1 | awk '{print $1 * 4096 / 1024 / 1024}'; > and for 64K using: > cat /proc/zoneinfo | grep -i min | awk '{print $2}' | sort -n | tail -n 1 | awk '{print $1 * 65536 / 1024 / 1024}'; > > An arbirtary min of 128 pages is used for when no hugepage sizes are set > enabled. > > Signed-off-by: Usama Arif > --- > include/linux/huge_mm.h | 25 +++++++++++++++++++++++++ > mm/khugepaged.c | 32 ++++++++++++++++++++++++++++---- > mm/shmem.c | 29 +++++------------------------ > 3 files changed, 58 insertions(+), 28 deletions(-) > > diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h > index 2f190c90192d..fb4e51ef0acb 100644 > --- a/include/linux/huge_mm.h > +++ b/include/linux/huge_mm.h > @@ -170,6 +170,25 @@ static inline void count_mthp_stat(int order, enum mthp_stat_item item) > } > #endif > > +/* > + * Definitions for "huge tmpfs": tmpfs mounted with the huge= option > + * > + * SHMEM_HUGE_NEVER: > + * disables huge pages for the mount; > + * SHMEM_HUGE_ALWAYS: > + * enables huge pages for the mount; > + * SHMEM_HUGE_WITHIN_SIZE: > + * only allocate huge pages if the page will be fully within i_size, > + * also respect madvise() hints; > + * SHMEM_HUGE_ADVISE: > + * only allocate huge pages if requested with madvise(); > + */ > + > + #define SHMEM_HUGE_NEVER 0 > + #define SHMEM_HUGE_ALWAYS 1 > + #define SHMEM_HUGE_WITHIN_SIZE 2 > + #define SHMEM_HUGE_ADVISE 3 > + > #ifdef CONFIG_TRANSPARENT_HUGEPAGE > > extern unsigned long transparent_hugepage_flags; > @@ -177,6 +196,12 @@ extern unsigned long huge_anon_orders_always; > extern unsigned long huge_anon_orders_madvise; > extern unsigned long huge_anon_orders_inherit; > > +extern int shmem_huge __read_mostly; > +extern unsigned long huge_shmem_orders_always; > +extern unsigned long huge_shmem_orders_madvise; > +extern unsigned long huge_shmem_orders_inherit; > +extern unsigned long huge_shmem_orders_within_size; Do really all of these have to be exported? > + > static inline bool hugepage_global_enabled(void) > { > return transparent_hugepage_flags & > diff --git a/mm/khugepaged.c b/mm/khugepaged.c > index 15203ea7d007..e64cba74eb2a 100644 > --- a/mm/khugepaged.c > +++ b/mm/khugepaged.c > @@ -2607,6 +2607,26 @@ static int khugepaged(void *none) > return 0; > } > > +static int thp_highest_allowable_order(void) Did you mean "largest" ? > +{ > + unsigned long orders = READ_ONCE(huge_anon_orders_always) > + | READ_ONCE(huge_anon_orders_madvise) > + | READ_ONCE(huge_shmem_orders_always) > + | READ_ONCE(huge_shmem_orders_madvise) > + | READ_ONCE(huge_shmem_orders_within_size); > + if (hugepage_global_enabled()) > + orders |= READ_ONCE(huge_anon_orders_inherit); > + if (shmem_huge != SHMEM_HUGE_NEVER) > + orders |= READ_ONCE(huge_shmem_orders_inherit); > + > + return orders == 0 ? 0 : fls(orders) - 1; > +} But how does this interact with large folios / THPs in the page cache? > + > +static unsigned long min_thp_pageblock_nr_pages(void) Reading the function name, I have no idea what this function is supposed to do. -- Cheers, David / dhildenb