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[2003:d8:2f1d:ed00:1769:dd7c:7208:eb33]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3b5e8dc201asm17251054f8f.22.2025.07.16.03.16.02 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 16 Jul 2025 03:16:03 -0700 (PDT) Message-ID: Date: Wed, 16 Jul 2025 12:16:02 +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 v3 2/4] mm/util: introduce snapshot_page() To: Luiz Capitulino , willy@infradead.org, akpm@linux-foundation.org Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, shivankg@amd.com, sj@kernel.org, harry.yoo@oracle.com References: <637a03a05cb2e3df88f84ff9e9f9642374ef813a.1752499009.git.luizcap@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/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: <637a03a05cb2e3df88f84ff9e9f9642374ef813a.1752499009.git.luizcap@redhat.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit [...] > > -dump: > - __dump_folio(foliop, &precise, pfn, idx); > + __dump_folio(&ps.folio_snapshot, &ps.page_snapshot, ps.pfn, ps.idx); Nit that can be cleaned up later on top: We should probably call this __dump_page_snapshot() and then just pass ... the page_snapshot. > } > > void dump_page(const struct page *page, const char *reason) > diff --git a/mm/util.c b/mm/util.c > index 0b270c43d7d1..f270bf42465b 100644 > --- a/mm/util.c > +++ b/mm/util.c > @@ -25,6 +25,7 @@ > #include > #include > #include > +#include > > #include > > @@ -1171,3 +1172,81 @@ int compat_vma_mmap_prepare(struct file *file, struct vm_area_struct *vma) > return 0; > } > EXPORT_SYMBOL(compat_vma_mmap_prepare); > + > +static void set_ps_flags(struct page_snapshot *ps, const struct folio *folio, > + const struct page *page) > +{ > + /* > + * Only the first page of a high-order buddy page has PageBuddy() set. > + * So we have to check manually whether this page is part of a high- > + * order buddy page. > + */ > + if (PageBuddy(page)) > + ps->flags |= PAGE_SNAPSHOT_PG_BUDDY; > + else if (page_count(page) == 0 && is_free_buddy_page(page)) > + ps->flags |= PAGE_SNAPSHOT_PG_BUDDY; > + > + if (folio_test_idle(folio)) > + ps->flags |= PAGE_SNAPSHOT_PG_IDLE; > +} > + > +/** > + * snapshot_page() - Create a snapshot of a struct page > + * @ps: Pointer to a struct page_snapshot to store the page snapshot > + * @page: The page to snapshot > + * > + * Create a snapshot of the page and store both its struct page and struct > + * folio representations in @ps. > + * > + * Note that creating a faithful snapshot may fail if the compound Maybe highlight that this is not really expected to happen, ever. > + * state of the page keeps changing (e.g., due to a folio split). In > + * this case, ps->faithful is set to false, and the snapshot assumes There is no ps->faithful. > + * that @page refers to a single page. > + */ > +void snapshot_page(struct page_snapshot *ps, const struct page *page) > +{ > + unsigned long head, nr_pages = 1; > + struct folio *foliop; > + int loops = 5; > + > + ps->pfn = page_to_pfn(page); > + ps->flags = PAGE_SNAPSHOT_FAITHFUL; > + > +again: > + memset(&ps->folio_snapshot, 0, sizeof(struct folio)); > + memcpy(&ps->page_snapshot, page, sizeof(*page)); > + head = ps->page_snapshot.compound_head; > + if ((head & 1) == 0) { > + ps->idx = 0; > + foliop = (struct folio *)&ps->page_snapshot; > + if (!folio_test_large(foliop)) { > + set_ps_flags(ps, page_folio(page), page); > + memcpy(&ps->folio_snapshot, foliop, > + sizeof(struct page)); > + return; > + } > + foliop = (struct folio *)page; > + } else { > + foliop = (struct folio *)(head - 1); > + ps->idx = folio_page_idx(foliop, page); > + } Condition could be cleaned up by reversing both things if (head & 1) { /* Tail page, lookup the actual head. */ foliop = (struct folio *)(head - 1); ps->idx = folio_page_idx(foliop, page); } else ... } But you're just moving that code, so no need to do that now. I think we could improve some of that in the future a bit to make it even more faithful. But for now this should be just fine. Acked-by: David Hildenbrand -- Cheers, David / dhildenb