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(p200300cbc7442200bad795bde25e0a9e.dip0.t-ipconnect.de. [2003:cb:c744:2200:bad7:95bd:e25e:a9e]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4266f7361b5sm10565245e9.29.2024.07.08.13.21.10 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 08 Jul 2024 13:21:11 -0700 (PDT) Message-ID: <75d6c45d-deea-464d-b0fd-b36e5d73b898@redhat.com> Date: Mon, 8 Jul 2024 22:21:09 +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 v21 1/4] mm: add VM_DROPPABLE for designating always lazily freeable mappings To: "Jason A. Donenfeld" Cc: Linus Torvalds , linux-kernel@vger.kernel.org, patches@lists.linux.dev, tglx@linutronix.de, linux-crypto@vger.kernel.org, linux-api@vger.kernel.org, x86@kernel.org, Greg Kroah-Hartman , Adhemerval Zanella Netto , Carlos O'Donell , Florian Weimer , Arnd Bergmann , Jann Horn , Christian Brauner , David Hildenbrand , linux-mm@kvack.org References: <20240707002658.1917440-1-Jason@zx2c4.com> <20240707002658.1917440-2-Jason@zx2c4.com> <1583c837-a4d5-4a8a-9c1d-2c64548cd199@redhat.com> <6705c6c8-8b6a-4d03-ae0f-aa83442ec0ab@redhat.com> <7439da2e-4a60-4643-9804-17e99ce6e312@redhat.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: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 08.07.24 16:40, Jason A. Donenfeld wrote: > Hi David, Linus, > > Below is what I understand the suggestions about the UX to be. The full > commit is in https://git.zx2c4.com/linux-rng/log/ but here's the part > we've been discussing. I've held off on David's suggestion changing > "DROPPABLE" to "VOLATILE" to give Linus some time to wake up on the west > coast and voice his preference for "DROPPABLE". But the rest is in > place. > > Jason > > diff --git a/include/uapi/linux/mman.h b/include/uapi/linux/mman.h > index a246e11988d5..e89d00528f2f 100644 > --- a/include/uapi/linux/mman.h > +++ b/include/uapi/linux/mman.h > @@ -17,6 +17,7 @@ > #define MAP_SHARED 0x01 /* Share changes */ > #define MAP_PRIVATE 0x02 /* Changes are private */ > #define MAP_SHARED_VALIDATE 0x03 /* share + validate extension flags */ > +#define MAP_DROPPABLE 0x08 /* Zero memory under memory pressure. */ > > /* > * Huge page size encoding when MAP_HUGETLB is specified, and a huge page > diff --git a/mm/madvise.c b/mm/madvise.c > index a77893462b92..cba5bc652fc4 100644 > --- a/mm/madvise.c > +++ b/mm/madvise.c > @@ -1068,13 +1068,16 @@ static int madvise_vma_behavior(struct vm_area_struct *vma, > new_flags |= VM_WIPEONFORK; > break; > case MADV_KEEPONFORK: > + if (vma->vm_flags & VM_DROPPABLE) > + return -EINVAL; > new_flags &= ~VM_WIPEONFORK; > break; > case MADV_DONTDUMP: > new_flags |= VM_DONTDUMP; > break; > case MADV_DODUMP: > - if (!is_vm_hugetlb_page(vma) && new_flags & VM_SPECIAL) > + if ((!is_vm_hugetlb_page(vma) && new_flags & VM_SPECIAL) || > + (vma->vm_flags & VM_DROPPABLE)) > return -EINVAL; > new_flags &= ~VM_DONTDUMP; > break; > diff --git a/mm/mlock.c b/mm/mlock.c > index 30b51cdea89d..b87b3d8cc9cc 100644 > --- a/mm/mlock.c > +++ b/mm/mlock.c > @@ -485,7 +485,7 @@ static int mlock_fixup(struct vma_iterator *vmi, struct vm_area_struct *vma, > > if (newflags == oldflags || (oldflags & VM_SPECIAL) || > is_vm_hugetlb_page(vma) || vma == get_gate_vma(current->mm) || > - vma_is_dax(vma) || vma_is_secretmem(vma)) > + vma_is_dax(vma) || vma_is_secretmem(vma) || (oldflags & VM_DROPPABLE)) > /* don't set VM_LOCKED or VM_LOCKONFAULT and don't count */ > goto out; > > diff --git a/mm/mmap.c b/mm/mmap.c > index 83b4682ec85c..b3d38179dd42 100644 > --- a/mm/mmap.c > +++ b/mm/mmap.c > @@ -1369,6 +1369,34 @@ unsigned long do_mmap(struct file *file, unsigned long addr, > pgoff = 0; > vm_flags |= VM_SHARED | VM_MAYSHARE; > break; > + case MAP_DROPPABLE: > + /* > + * A locked or stack area makes no sense to be droppable. > + * > + * Also, since droppable pages can just go away at any time > + * it makes no sense to copy them on fork or dump them. > + * > + * And don't attempt to combine with hugetlb for now. > + */ > + if (flags & (MAP_LOCKED | MAP_HUGETLB)) > + return -EINVAL; > + if (vm_flags & (VM_GROWSDOWN | VM_GROWSUP)) > + return -EINVAL; > + > + vm_flags |= VM_DROPPABLE; > + > + /* > + * If the pages can be dropped, then it doesn't make > + * sense to reserve them. > + */ > + vm_flags |= VM_NORESERVE; That is certainly interesting. Nothing that we might not be able to reclaim these pages reliably in all cases: for example when long-term pinning them. In some environments (OVERCOMMIT_NEVER) MAP_NORESERE would never be effective. I wonder if we want to stick to the same behavior here ... but in theory I agree that we can set this here unconditionally, it's just the corner case of "there are ways to prohibit reclaim" that makes me wonder. BTW, I was just trying to understand how MADV_FREE + MAP_DROPPABLE would behave without any swap space around. Did you experiment with that? I'm reading can_reclaim_anon_pages(), and I'm wondering how good/reliable that works when there is no swap configured. Also, the comment in get_scan_count(): "If we have no swap space, do not bother scanning anon folios." makes me wonder if some work in that area is needed. -- Cheers, David / dhildenb