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[2003:d8:2f44:3700:be07:9a67:67f7:24e6]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-458953cfe56sm72071135e9.20.2025.07.31.07.54.38 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 31 Jul 2025 07:54:39 -0700 (PDT) Message-ID: <747509a6-8493-46c3-99d4-38b53a8a7504@redhat.com> Date: Thu, 31 Jul 2025 16:54:38 +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 v2 3/5] mm/huge_memory: treat MADV_COLLAPSE as an advise with PR_THP_DISABLE_EXCEPT_ADVISED To: Lorenzo Stoakes , Usama Arif Cc: Andrew Morton , linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, corbet@lwn.net, rppt@kernel.org, surenb@google.com, mhocko@suse.com, hannes@cmpxchg.org, baohua@kernel.org, shakeel.butt@linux.dev, riel@surriel.com, ziy@nvidia.com, laoar.shao@gmail.com, dev.jain@arm.com, baolin.wang@linux.alibaba.com, npache@redhat.com, Liam.Howlett@oracle.com, ryan.roberts@arm.com, vbabka@suse.cz, jannh@google.com, Arnd Bergmann , sj@kernel.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, kernel-team@meta.com References: <20250731122825.2102184-1-usamaarif642@gmail.com> <20250731122825.2102184-4-usamaarif642@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: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 31.07.25 16:38, Lorenzo Stoakes wrote: > Nits on subject: > > - It's >75 chars No big deal. If we cna come up with something shorter, good. > - advise is the verb, advice is the noun. Yeah. > > On Thu, Jul 31, 2025 at 01:27:20PM +0100, Usama Arif wrote: >> From: David Hildenbrand >> >> Let's allow for making MADV_COLLAPSE succeed on areas that neither have >> VM_HUGEPAGE nor VM_NOHUGEPAGE when we have THP disabled >> unless explicitly advised (PR_THP_DISABLE_EXCEPT_ADVISED). > > Hmm, I'm not sure about this. > > So far this prctl() has been the only way to override MADV_COLLAPSE > behaviour, but now we're allowing for this one case to not. This is not an override really. prctl() disallowed MADV_COLLAPSE, but in the new mode we don't want that anymore. > > I suppose the precedent is that MADV_COLLAPSE overrides 'madvise' sysfs > behaviour. > > I suppose what saves us here is 'advised' can be read to mean either > MADV_HUGEPAGE or MADV_COLLAPSE. > > And yes, MADV_COLLAPSE is clearly the user requesting this behaviour. Exactly. > > I think the vagueness here is one that already existed, because one could > perfectly one have expected MADV_COLLAPSE to obey sysfs and require > MADV_HUGEPAGE to have been applied, but of course this is not the case. Yes. > > OK so fine. > > BUT. > > I think the MADV_COLLAPSE man page will need to be updated to mention this. > Yes. > And I REALLY think we should update the THP doc too to mention all these > prctl() modes. > > I'm not sure we cover that right now _at all_ and obviously we should > describe the new flags. > > Usama - can you add a patch to this series to do that? Good point, let's document the interaction with prctl(). > >> >> MADV_COLLAPSE is a clear advise that we want to collapse. > > advise -> advice. > >> >> Note that we still respect the VM_NOHUGEPAGE flag, just like >> MADV_COLLAPSE always does. So consequently, MADV_COLLAPSE is now only >> refused on VM_NOHUGEPAGE with PR_THP_DISABLE_EXCEPT_ADVISED. > > You also need to mention the shmem change you've made I think. Yes. > >> >> Co-developed-by: Usama Arif >> Signed-off-by: Usama Arif >> Signed-off-by: David Hildenbrand >> --- >> include/linux/huge_mm.h | 8 +++++++- >> include/uapi/linux/prctl.h | 2 +- >> mm/huge_memory.c | 5 +++-- >> mm/memory.c | 6 ++++-- >> mm/shmem.c | 2 +- >> 5 files changed, 16 insertions(+), 7 deletions(-) >> >> diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h >> index b0ff54eee81c..aeaf93f8ac2e 100644 >> --- a/include/linux/huge_mm.h >> +++ b/include/linux/huge_mm.h >> @@ -329,7 +329,7 @@ struct thpsize { >> * through madvise or prctl. >> */ >> static inline bool vma_thp_disabled(struct vm_area_struct *vma, >> - vm_flags_t vm_flags) >> + vm_flags_t vm_flags, bool forced_collapse) >> { >> /* Are THPs disabled for this VMA? */ >> if (vm_flags & VM_NOHUGEPAGE) >> @@ -343,6 +343,12 @@ static inline bool vma_thp_disabled(struct vm_area_struct *vma, >> */ >> if (vm_flags & VM_HUGEPAGE) >> return false; >> + /* >> + * Forcing a collapse (e.g., madv_collapse), is a clear advise to > > advise -> advice. > >> + * use THPs. >> + */ >> + if (forced_collapse) >> + return false; >> return test_bit(MMF_DISABLE_THP_EXCEPT_ADVISED, &vma->vm_mm->flags); >> } >> >> diff --git a/include/uapi/linux/prctl.h b/include/uapi/linux/prctl.h >> index 9c1d6e49b8a9..ee4165738779 100644 >> --- a/include/uapi/linux/prctl.h >> +++ b/include/uapi/linux/prctl.h >> @@ -185,7 +185,7 @@ struct prctl_mm_map { >> #define PR_SET_THP_DISABLE 41 >> /* >> * Don't disable THPs when explicitly advised (e.g., MADV_HUGEPAGE / >> - * VM_HUGEPAGE). >> + * VM_HUGEPAGE / MADV_COLLAPSE). > > This is confusing you're mixing VMA flags with MADV ones... maybe just > stick to madvise ones, or add extra context around VM_HUGEPAGE bit? I don't see anything confusing here, really. But if it helps you, we can do (e.g., MADV_HUGEPAGE / VM_HUGEPAGE, MADV_COLLAPSE). (reason VM_HUGEPAGE is spelled out is that there might be code where we set VM_HUGEPAGE implicitly in the kernel) > > Would need to be fixed up in a prior commit obviously. > >> */ >> # define PR_THP_DISABLE_EXCEPT_ADVISED (1 << 1) >> #define PR_GET_THP_DISABLE 42 >> diff --git a/mm/huge_memory.c b/mm/huge_memory.c >> index 85252b468f80..ef5ccb0ec5d5 100644 >> --- a/mm/huge_memory.c >> +++ b/mm/huge_memory.c >> @@ -104,7 +104,8 @@ unsigned long __thp_vma_allowable_orders(struct vm_area_struct *vma, >> { >> const bool smaps = type == TVA_SMAPS; >> const bool in_pf = type == TVA_PAGEFAULT; >> - const bool enforce_sysfs = type != TVA_FORCED_COLLAPSE; >> + const bool forced_collapse = type == TVA_FORCED_COLLAPSE; >> + const bool enforce_sysfs = !forced_collapse; > > Can we just get rid of this enforce_sysfs altogether in patch 2/5 and use > forced_collapse? Let's do that as a separate cleanup on top. I want least churn in that patch. (had the same idea while writing that patch, but I have other things to focus on than cleaning up all this mess) -- Cheers, David / dhildenb