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(p200300cbc74bca004ca2ff2c9092f070.dip0.t-ipconnect.de. [2003:cb:c74b:ca00:4ca2:ff2c:9092:f070]) by smtp.gmail.com with ESMTPSA id n4-20020a5d6b84000000b0033634aef014sm1326595wrx.104.2023.12.12.08.35.23 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 12 Dec 2023 08:35:24 -0800 (PST) Message-ID: Date: Tue, 12 Dec 2023 17:35:23 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v9 04/10] mm: thp: Support allocation of anonymous multi-size THP To: Ryan Roberts , Andrew Morton , Matthew Wilcox , Yin Fengwei , Yu Zhao , Catalin Marinas , Anshuman Khandual , Yang Shi , "Huang, Ying" , Zi Yan , Luis Chamberlain , Itaru Kitayama , "Kirill A. Shutemov" , John Hubbard , David Rientjes , Vlastimil Babka , Hugh Dickins , Kefeng Wang , Barry Song <21cnbao@gmail.com>, Alistair Popple Cc: linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org References: <20231207161211.2374093-1-ryan.roberts@arm.com> <20231207161211.2374093-5-ryan.roberts@arm.com> <2bebcf33-e8b7-468d-86cc-31d6eb355b66@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-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspamd-Queue-Id: 1BA8440039 X-Rspam-User: X-Stat-Signature: z1pyeyxg7imb7rpzw9gdh7d7cn7e5syw X-Rspamd-Server: rspam03 X-HE-Tag: 1702398928-648220 X-HE-Meta: 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 YNqK+JZ6 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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 12.12.23 16:38, Ryan Roberts wrote: > On 12/12/2023 15:02, David Hildenbrand wrote: >> On 07.12.23 17:12, Ryan Roberts wrote: >>> Introduce the logic to allow THP to be configured (through the new sysfs >>> interface we just added) to allocate large folios to back anonymous >>> memory, which are larger than the base page size but smaller than >>> PMD-size. We call this new THP extension "multi-size THP" (mTHP). >>> >>> mTHP continues to be PTE-mapped, but in many cases can still provide >>> similar benefits to traditional PMD-sized THP: Page faults are >>> significantly reduced (by a factor of e.g. 4, 8, 16, etc. depending on >>> the configured order), but latency spikes are much less prominent >>> because the size of each page isn't as huge as the PMD-sized variant and >>> there is less memory to clear in each page fault. The number of per-page >>> operations (e.g. ref counting, rmap management, lru list management) are >>> also significantly reduced since those ops now become per-folio. >> >> I'll note that with always-pte-mapped-thp it will be much easier to support >> incremental page clearing (e.g., zero only parts of the folio and map the >> remainder in a pro-non-like fashion whereby we'll zero on the next page fault). >> With a PMD-sized thp, you have to eventually place/rip out page tables to >> achieve that. > > But then you lose the benefits of reduced number of page faults; reducing page > faults gives a big speed up for workloads with lots of short lived processes > like compiling. Well, you can do interesting things like "allocate order-5", but zero in order-3 chunks. You get less page faults and pay for alloc/rmap only once. But yes, all has pros and cons. [...] >> >>> >>> Some architectures also employ TLB compression mechanisms to squeeze >>> more entries in when a set of PTEs are virtually and physically >>> contiguous and approporiately aligned. In this case, TLB misses will >>> occur less often. >>> >>> The new behaviour is disabled by default, but can be enabled at runtime >>> by writing to /sys/kernel/mm/transparent_hugepage/hugepage-XXkb/enabled >>> (see documentation in previous commit). The long term aim is to change >>> the default to include suitable lower orders, but there are some risks >>> around internal fragmentation that need to be better understood first. >>> >>> Tested-by: Kefeng Wang >>> Tested-by: John Hubbard >>> Signed-off-by: Ryan Roberts >>> --- >>>   include/linux/huge_mm.h |   6 ++- >>>   mm/memory.c             | 111 ++++++++++++++++++++++++++++++++++++---- >>>   2 files changed, 106 insertions(+), 11 deletions(-) >>> >>> diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h >>> index 609c153bae57..fa7a38a30fc6 100644 >>> --- a/include/linux/huge_mm.h >>> +++ b/include/linux/huge_mm.h >>> @@ -68,9 +68,11 @@ extern struct kobj_attribute shmem_enabled_attr; >>>   #define HPAGE_PMD_NR (1<> >> [...] >> >>> + >>> +#ifdef CONFIG_TRANSPARENT_HUGEPAGE >>> +static struct folio *alloc_anon_folio(struct vm_fault *vmf) >>> +{ >>> +    struct vm_area_struct *vma = vmf->vma; >>> +    unsigned long orders; >>> +    struct folio *folio; >>> +    unsigned long addr; >>> +    pte_t *pte; >>> +    gfp_t gfp; >>> +    int order; >>> + >>> +    /* >>> +     * If uffd is active for the vma we need per-page fault fidelity to >>> +     * maintain the uffd semantics. >>> +     */ >>> +    if (unlikely(userfaultfd_armed(vma))) >>> +        goto fallback; >>> + >>> +    /* >>> +     * Get a list of all the (large) orders below PMD_ORDER that are enabled >>> +     * for this vma. Then filter out the orders that can't be allocated over >>> +     * the faulting address and still be fully contained in the vma. >>> +     */ >>> +    orders = thp_vma_allowable_orders(vma, vma->vm_flags, false, true, true, >>> +                      BIT(PMD_ORDER) - 1); >>> +    orders = thp_vma_suitable_orders(vma, vmf->address, orders); >>> + >>> +    if (!orders) >>> +        goto fallback; >>> + >>> +    pte = pte_offset_map(vmf->pmd, vmf->address & PMD_MASK); >>> +    if (!pte) >>> +        return ERR_PTR(-EAGAIN); >>> + >>> +    /* >>> +     * Find the highest order where the aligned range is completely >>> +     * pte_none(). Note that all remaining orders will be completely >>> +     * pte_none(). >>> +     */ >>> +    order = highest_order(orders); >>> +    while (orders) { >>> +        addr = ALIGN_DOWN(vmf->address, PAGE_SIZE << order); >>> +        if (pte_range_none(pte + pte_index(addr), 1 << order)) >>> +            break; >>> +        order = next_order(&orders, order); >>> +    } >>> + >>> +    pte_unmap(pte); >>> + >>> +    /* Try allocating the highest of the remaining orders. */ >>> +    gfp = vma_thp_gfp_mask(vma); >>> +    while (orders) { >>> +        addr = ALIGN_DOWN(vmf->address, PAGE_SIZE << order); >>> +        folio = vma_alloc_folio(gfp, order, vma, addr, true); >>> +        if (folio) { >>> +            clear_huge_page(&folio->page, vmf->address, 1 << order); >>> +            return folio; >>> +        } >>> +        order = next_order(&orders, order); >>> +    } >>> + >>> +fallback: >>> +    return vma_alloc_zeroed_movable_folio(vma, vmf->address); >>> +} >>> +#else >>> +#define alloc_anon_folio(vmf) \ >>> +        vma_alloc_zeroed_movable_folio((vmf)->vma, (vmf)->address) >>> +#endif >> >> A neater alternative might be >> >> static struct folio *alloc_anon_folio(struct vm_fault *vmf) >> { >> #ifdef CONFIG_TRANSPARENT_HUGEPAGE >>     /* magic */ >> fallback: >> #endif >>     return vma_alloc_zeroed_movable_folio((vmf)->vma, (vmf)->address): >> } > > I guess beauty lies in the eye of the beholder... I don't find it much neater > personally :). But happy to make the change if you insist; what's the process > now that its in mm-unstable? Just send a patch to Andrew for squashing? That way it is clear that the fallback for thp is just what !thp does. But either is fine for me; no need to change if you disagree. -- Cheers, David / dhildenb