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(p200300d82f34ae00cf93b0dc6bed0abc.dip0.t-ipconnect.de. [2003:d8:2f34:ae00:cf93:b0dc:6bed:abc]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-45870532a4csm53826245e9.7.2025.07.25.06.08.24 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 25 Jul 2025 06:08:25 -0700 (PDT) Message-ID: <0905a63e-420e-484f-a98b-19e85fc851fa@redhat.com> Date: Fri, 25 Jul 2025 15:08:24 +0200 Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH POC] prctl: extend PR_SET_THP_DISABLE to optionally exclude VM_HUGEPAGE To: Usama Arif , linux-kernel@vger.kernel.org Cc: linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-doc@vger.kernel.org, Jonathan Corbet , Andrew Morton , Lorenzo Stoakes , Zi Yan , Baolin Wang , "Liam R. Howlett" , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , SeongJae Park , Jann Horn , Yafang Shao , Matthew Wilcox , Johannes Weiner References: <20250721090942.274650-1-david@redhat.com> <3ec01250-0ff3-4d04-9009-7b85b6058e41@gmail.com> <601e015b-1f61-45e8-9db8-4e0d2bc1505e@redhat.com> <99e25828-641b-490b-baab-35df860760b4@gmail.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/g1oFAmgsLPQFCRvGjuMACgkQTd4Q 9wD/g1o0bxAAqYC7gTyGj5rZwvy1VesF6YoQncH0yI79lvXUYOX+Nngko4v4dTlOQvrd/vhb 02e9FtpA1CxgwdgIPFKIuXvdSyXAp0xXuIuRPQYbgNriQFkaBlHe9mSf8O09J3SCVa/5ezKM OLW/OONSV/Fr2VI1wxAYj3/Rb+U6rpzqIQ3Uh/5Rjmla6pTl7Z9/o1zKlVOX1SxVGSrlXhqt kwdbjdj/csSzoAbUF/duDuhyEl11/xStm/lBMzVuf3ZhV5SSgLAflLBo4l6mR5RolpPv5wad GpYS/hm7HsmEA0PBAPNb5DvZQ7vNaX23FlgylSXyv72UVsObHsu6pT4sfoxvJ5nJxvzGi69U s1uryvlAfS6E+D5ULrV35taTwSpcBAh0/RqRbV0mTc57vvAoXofBDcs3Z30IReFS34QSpjvl Hxbe7itHGuuhEVM1qmq2U72ezOQ7MzADbwCtn+yGeISQqeFn9QMAZVAkXsc9Wp0SW/WQKb76 FkSRalBZcc2vXM0VqhFVzTb6iNqYXqVKyuPKwhBunhTt6XnIfhpRgqveCPNIasSX05VQR6/a OBHZX3seTikp7A1z9iZIsdtJxB88dGkpeMj6qJ5RLzUsPUVPodEcz1B5aTEbYK6428H8MeLq NFPwmknOlDzQNC6RND8Ez7YEhzqvw7263MojcmmPcLelYbfOwU0EVcufkQEQAOfX3n0g0fZz 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+DWgUCaCwtJQUJG8aPFAAKCRBN3hD3AP+DWlDnD/4k2TW+HyOOOePVm23F5HOhNNd7nNv3 Vq2cLcW1DteHUdxMO0X+zqrKDHI5hgnE/E2QH9jyV8mB8l/ndElobciaJcbl1cM43vVzPIWn 01vW62oxUNtEvzLLxGLPTrnMxWdZgxr7ACCWKUnMGE2E8eca0cT2pnIJoQRz242xqe/nYxBB /BAK+dsxHIfcQzl88G83oaO7vb7s/cWMYRKOg+WIgp0MJ8DO2IU5JmUtyJB+V3YzzM4cMic3 bNn8nHjTWw/9+QQ5vg3TXHZ5XMu9mtfw2La3bHJ6AybL0DvEkdGxk6YHqJVEukciLMWDWqQQ RtbBhqcprgUxipNvdn9KwNpGciM+hNtM9kf9gt0fjv79l/FiSw6KbCPX9b636GzgNy0Ev2UV m00EtcpRXXMlEpbP4V947ufWVK2Mz7RFUfU4+ETDd1scMQDHzrXItryHLZWhopPI4Z+ps0rB CQHfSpl+wG4XbJJu1D8/Ww3FsO42TMFrNr2/cmqwuUZ0a0uxrpkNYrsGjkEu7a+9MheyTzcm vyU2knz5/stkTN2LKz5REqOe24oRnypjpAfaoxRYXs+F8wml519InWlwCra49IUSxD1hXPxO WBe5lqcozu9LpNDH/brVSzHCSb7vjNGvvSVESDuoiHK8gNlf0v+epy5WYd7CGAgODPvDShGN g3eXuA== Organization: Red Hat In-Reply-To: <99e25828-641b-490b-baab-35df860760b4@gmail.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 25.07.25 00:27, Usama Arif wrote: > >> Hi! >> >>> >>> Over here, with MMF_DISABLE_THP_EXCEPT_ADVISED, MADV_HUGEPAGE will succeed as vm_flags has >>> VM_HUGEPAGE set, but MADV_COLLAPSE will fail to give a hugepage (as VM_HUGEPAGE is not set >>> and MMF_DISABLE_THP_EXCEPT_ADVISED is set) which I feel might not be the right behaviour >>> as MADV_COLLAPSE is "advise" and the prctl flag is PR_THP_DISABLE_EXCEPT_ADVISED? >> >> THPs are disabled for these regions, so it's at least consistent with the "disable all", but ... >> >>> >>> This will be checked in multiple places in madvise_collapse: thp_vma_allowable_order, >>> hugepage_vma_revalidate which calls thp_vma_allowable_order and hpage_collapse_scan_pmd >>> which also ends up calling hugepage_vma_revalidate. >>>> A hacky way would be to save and overwrite vma->vm_flags with VM_HUGEPAGE at the start of madvise_collapse >>> if VM_NOHUGEPAGE is not set, and reset vma->vm_flags to its original value at the end of madvise_collapse >>> (Not something I am recommending, just throwing it out there). >> >> Gah. >> >>> >>> Another possibility is to pass the fact that you are in madvise_collapse to these functions >>> as an argument, this might look ugly, although maybe not as ugly as hugepage_vma_revalidate >>> already has collapse control arg, so just need to take care of thp_vma_allowable_orders. >> >> Likely this. >> >>> >>> Any preference or better suggestions? >> >> What you are asking for is not MMF_DISABLE_THP_EXCEPT_ADVISED as I planned it, but MMF_DISABLE_THP_EXCEPT_ADVISED_OR_MADV_COLLAPSE. >> >> Now, one could consider MADV_COLLAPSE an "advise". (I am not opposed to that change) >> > > lol yeah I always think of MADV_COLLAPSE as an extreme version of MADV_HUGE (more of a demand > than an advice :)), eventhough its not persistant. > Which is why I think might be unexpected if MADV_HUGE gives hugepages but MADV_COLLAPSE doesn't > (But could just be my opinion). > >> Indeed, the right way might be telling vma_thp_disabled() whether we are in collapse. >> >> Can you try implementing that on top of my patch to see how it looks? >> > > My reasoning is that a process that is running with system policy always but with > PR_THP_DISABLE_EXCEPT_ADVISED gets THPs in exactly the same behaviour as a process that is running > with system policy madvise. This will help us achieve (3) that you mentioned in the > commit message: > (3) Switch from THP=madvise to THP=always, but keep the old behavior > (THP only when advised) for selected workloads. > > > I have written quite a few selftests now for prctl SET_THP_DISABLE, both with and without > PR_THP_DISABLE_EXCEPT_ADVISED set incorporating your feedback on it. I have all of them passing > with the below diff. The diff is slightly ugly, but very simple and hopefully acceptable. If it > looks good, I can send a series with everything. Probably make the below diff as a separate patch > on top of this patch as its mostly adding an extra arg to functions and would keep the review easier? Yes, we should do it as a separate patch, makes our life easier, because that requires more work. We require a cleanup first, the boolean parameter for __thp_vma_allowable_orders() is no good. I just pushed something untested to my branch (slightly adjusted patch#1 + 2 more patches), can you have a look at that? (untested ... :) ) -- Cheers, David / dhildenb