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(p200300d82f187500202eb0f176d6f9af.dip0.t-ipconnect.de. [2003:d8:2f18:7500:202e:b0f1:76d6:f9af]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-453823b913esm191229535e9.33.2025.07.01.05.41.04 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 01 Jul 2025 05:41:06 -0700 (PDT) Message-ID: Date: Tue, 1 Jul 2025 14:41:03 +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 v1 19/29] mm: stop storing migration_ops in page->mapping To: Lorenzo Stoakes Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-doc@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, virtualization@lists.linux.dev, linux-fsdevel@vger.kernel.org, Andrew Morton , Jonathan Corbet , Madhavan Srinivasan , Michael Ellerman , Nicholas Piggin , Christophe Leroy , Jerrin Shaji George , Arnd Bergmann , Greg Kroah-Hartman , "Michael S. Tsirkin" , Jason Wang , Xuan Zhuo , =?UTF-8?Q?Eugenio_P=C3=A9rez?= , Alexander Viro , Christian Brauner , Jan Kara , Zi Yan , Matthew Brost , Joshua Hahn , Rakie Kim , Byungchul Park , Gregory Price , Ying Huang , Alistair Popple , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , "Matthew Wilcox (Oracle)" , Minchan Kim , Sergey Senozhatsky , Brendan Jackman , Johannes Weiner , Jason Gunthorpe , John Hubbard , Peter Xu , Xu Xin , Chengming Zhou , Miaohe Lin , Naoya Horiguchi , Oscar Salvador , Rik van Riel , Harry Yoo , Qi Zheng , Shakeel Butt References: <20250630130011.330477-1-david@redhat.com> <20250630130011.330477-20-david@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 01.07.25 14:12, Lorenzo Stoakes wrote: > On Mon, Jun 30, 2025 at 03:00:00PM +0200, David Hildenbrand wrote: >> ... instead, look them up statically based on the page type. Maybe in the >> future we want a registration interface? At least for now, it can be >> easily handled using the two page types that actually support page >> migration. >> >> The remaining usage of page->mapping is to flag such pages as actually >> being movable (having movable_ops), which we will change next. >> >> Reviewed-by: Zi Yan >> Signed-off-by: David Hildenbrand > > See comment below, this feels iffy in the long run but ok as an interim measure. > > So: > > Reviewed-by: Lorenzo Stoakes > >> --- >> include/linux/balloon_compaction.h | 2 +- >> include/linux/migrate.h | 14 ++------------ >> include/linux/zsmalloc.h | 2 ++ >> mm/balloon_compaction.c | 1 - >> mm/compaction.c | 5 ++--- >> mm/migrate.c | 23 +++++++++++++++++++++++ >> mm/zpdesc.h | 5 ++--- >> mm/zsmalloc.c | 8 +++----- >> 8 files changed, 35 insertions(+), 25 deletions(-) >> >> diff --git a/include/linux/balloon_compaction.h b/include/linux/balloon_compaction.h >> index 9bce8e9f5018c..a8a1706cc56f3 100644 >> --- a/include/linux/balloon_compaction.h >> +++ b/include/linux/balloon_compaction.h >> @@ -92,7 +92,7 @@ static inline void balloon_page_insert(struct balloon_dev_info *balloon, >> struct page *page) >> { >> __SetPageOffline(page); >> - __SetPageMovable(page, &balloon_mops); >> + __SetPageMovable(page); >> set_page_private(page, (unsigned long)balloon); >> list_add(&page->lru, &balloon->pages); >> } >> diff --git a/include/linux/migrate.h b/include/linux/migrate.h >> index e04035f70e36f..6aece3f3c8be8 100644 >> --- a/include/linux/migrate.h >> +++ b/include/linux/migrate.h >> @@ -104,23 +104,13 @@ static inline int migrate_huge_page_move_mapping(struct address_space *mapping, >> #endif /* CONFIG_MIGRATION */ >> >> #ifdef CONFIG_COMPACTION >> -void __SetPageMovable(struct page *page, const struct movable_operations *ops); >> +void __SetPageMovable(struct page *page); >> #else >> -static inline void __SetPageMovable(struct page *page, >> - const struct movable_operations *ops) >> +static inline void __SetPageMovable(struct page *page) >> { >> } >> #endif >> >> -static inline >> -const struct movable_operations *page_movable_ops(struct page *page) >> -{ >> - VM_WARN_ON_ONCE_PAGE(!page_has_movable_ops(page), page); >> - >> - return (const struct movable_operations *) >> - ((unsigned long)page->mapping - PAGE_MAPPING_MOVABLE); >> -} >> - >> #ifdef CONFIG_NUMA_BALANCING >> int migrate_misplaced_folio_prepare(struct folio *folio, >> struct vm_area_struct *vma, int node); >> diff --git a/include/linux/zsmalloc.h b/include/linux/zsmalloc.h >> index 13e9cc5490f71..f3ccff2d966cd 100644 >> --- a/include/linux/zsmalloc.h >> +++ b/include/linux/zsmalloc.h >> @@ -46,4 +46,6 @@ void zs_obj_read_end(struct zs_pool *pool, unsigned long handle, >> void zs_obj_write(struct zs_pool *pool, unsigned long handle, >> void *handle_mem, size_t mem_len); >> >> +extern const struct movable_operations zsmalloc_mops; >> + >> #endif >> diff --git a/mm/balloon_compaction.c b/mm/balloon_compaction.c >> index e4f1a122d786b..2a4a649805c11 100644 >> --- a/mm/balloon_compaction.c >> +++ b/mm/balloon_compaction.c >> @@ -253,6 +253,5 @@ const struct movable_operations balloon_mops = { >> .isolate_page = balloon_page_isolate, >> .putback_page = balloon_page_putback, >> }; >> -EXPORT_SYMBOL_GPL(balloon_mops); >> >> #endif /* CONFIG_BALLOON_COMPACTION */ >> diff --git a/mm/compaction.c b/mm/compaction.c >> index 41fd6a1fe9a33..348eb754cb227 100644 >> --- a/mm/compaction.c >> +++ b/mm/compaction.c >> @@ -114,11 +114,10 @@ static unsigned long release_free_list(struct list_head *freepages) >> } >> >> #ifdef CONFIG_COMPACTION >> -void __SetPageMovable(struct page *page, const struct movable_operations *mops) >> +void __SetPageMovable(struct page *page) >> { >> VM_BUG_ON_PAGE(!PageLocked(page), page); >> - VM_BUG_ON_PAGE((unsigned long)mops & PAGE_MAPPING_MOVABLE, page); >> - page->mapping = (void *)((unsigned long)mops | PAGE_MAPPING_MOVABLE); >> + page->mapping = (void *)(PAGE_MAPPING_MOVABLE); >> } >> EXPORT_SYMBOL(__SetPageMovable); >> >> diff --git a/mm/migrate.c b/mm/migrate.c >> index 15d3c1031530c..c6c9998014ec8 100644 >> --- a/mm/migrate.c >> +++ b/mm/migrate.c >> @@ -43,6 +43,8 @@ >> #include >> #include >> #include >> +#include >> +#include >> >> #include >> >> @@ -51,6 +53,27 @@ >> #include "internal.h" >> #include "swap.h" >> >> +static const struct movable_operations *page_movable_ops(struct page *page) >> +{ >> + VM_WARN_ON_ONCE_PAGE(!page_has_movable_ops(page), page); >> + >> + /* >> + * If we enable page migration for a page of a certain type by marking >> + * it as movable, the page type must be sticky until the page gets freed >> + * back to the buddy. >> + */ > > Ah now this makes more sense... > >> +#ifdef CONFIG_BALLOON_COMPACTION >> + if (PageOffline(page)) >> + /* Only balloon compaction sets PageOffline pages movable. */ >> + return &balloon_mops; > > So it's certain that if we try to invoke movable ops, and it's the balloon > compaction case, the page will be offline? Yes. The page must be marked as having movable_ops by the user. The next patch reworks that as well. A PageOffline page without movable_ops will never end up here (page_has_movable_ops() == false). > >> +#endif /* CONFIG_BALLOON_COMPACTION */ >> +#if defined(CONFIG_ZSMALLOC) && defined(CONFIG_COMPACTION) >> + if (PageZsmalloc(page)) > > And same question only for ZS malloc. Same thing. > >> + return &zsmalloc_mops; >> +#endif /* defined(CONFIG_ZSMALLOC) && defined(CONFIG_COMPACTION) */ >> + return NULL; >> +} > > This is kind of sketchy as it's baking in assumptions implicitly, so I hope we > can find an improved way of doing this later, even if it's about providing > e.g. is_ballon_movable_ops_page() and is_zsmalloc_movable_ops_page() predicates > that abstract this code + placing them in the relevant code so it's at least > obvious to people working on this stuff that this needs to be considered. > > But ok as a means of getting away from having to have the hook object encoded. Yeah, not sure yet how to clean that up in the future. As I stated somewhere, maybe we just want a registration interface to handle a specific page type. But for handling the two known in-tree users, this should get us going. Thanks! -- Cheers, David / dhildenb