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Fri, 5 Dec 2025 14:43:57 -0500 (EST) From: Kiryl Shutsemau To: Andrew Morton , Muchun Song Cc: David Hildenbrand , Oscar Salvador , Mike Rapoport , Vlastimil Babka , Lorenzo Stoakes , Matthew Wilcox , Zi Yan , Baoquan He , Michal Hocko , Johannes Weiner , Jonathan Corbet , Usama Arif , kernel-team@meta.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, Kiryl Shutsemau Subject: [PATCH 02/11] mm: Rename the 'compound_head' field in the 'struct page' to 'compound_info' Date: Fri, 5 Dec 2025 19:43:38 +0000 Message-ID: <20251205194351.1646318-3-kas@kernel.org> X-Mailer: git-send-email 2.51.2 In-Reply-To: <20251205194351.1646318-1-kas@kernel.org> References: <20251205194351.1646318-1-kas@kernel.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Queue-Id: DC3778000D X-Stat-Signature: db37xrmmh995bf7qxn4wgbuxudprugca X-Rspam-User: X-Rspamd-Server: rspam02 X-HE-Tag: 1764963839-993982 X-HE-Meta: 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 4H03RCdW EQuq/hGLACbrf45q9DoCDyA0vnQQ5V0p1IZkWZRIxafoFzS4R6LCRA4YDMCNyVwySBiuOaWFrYRIVQf3oW1urjlwpnHVLHhh2AGJ6cl7erDEsOpSCnFuGYPcrB77anrKBM1yGbCb1A7oZ0A1bg4U5g3PFDSSFkqpd8Ect69+P1Pok3jtX5uobGuvRGA+IVoSn2I9bnLJaq6AR5D9DbU/WJrzZwGI037HTcCVb2QeNwgosNNPIjmM03Q4GFXg4O521gjITK/O1w2uqGMQHk0iEHCnYS+tc0i6oJjsNLE55lcWefbXHP2jX5oDBCg== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: The 'compound_head' field in the 'struct page' encodes whether the page is a tail and where to locate the head page. Bit 0 is set if the page is a tail, and the remaining bits in the field point to the head page. As preparation for changing how the field encodes information about the head page, rename the field to 'compound_info'. Signed-off-by: Kiryl Shutsemau --- .../admin-guide/kdump/vmcoreinfo.rst | 2 +- Documentation/mm/vmemmap_dedup.rst | 6 +++--- include/linux/mm_types.h | 20 +++++++++---------- include/linux/page-flags.h | 18 ++++++++--------- include/linux/types.h | 2 +- kernel/vmcore_info.c | 2 +- mm/page_alloc.c | 2 +- mm/slab.h | 2 +- mm/util.c | 2 +- 9 files changed, 28 insertions(+), 28 deletions(-) diff --git a/Documentation/admin-guide/kdump/vmcoreinfo.rst b/Documentation/admin-guide/kdump/vmcoreinfo.rst index 404a15f6782c..7663c610fe90 100644 --- a/Documentation/admin-guide/kdump/vmcoreinfo.rst +++ b/Documentation/admin-guide/kdump/vmcoreinfo.rst @@ -141,7 +141,7 @@ nodemask_t The size of a nodemask_t type. Used to compute the number of online nodes. -(page, flags|_refcount|mapping|lru|_mapcount|private|compound_order|compound_head) +(page, flags|_refcount|mapping|lru|_mapcount|private|compound_order|compound_info) ---------------------------------------------------------------------------------- User-space tools compute their values based on the offset of these diff --git a/Documentation/mm/vmemmap_dedup.rst b/Documentation/mm/vmemmap_dedup.rst index b4a55b6569fa..1863d88d2dcb 100644 --- a/Documentation/mm/vmemmap_dedup.rst +++ b/Documentation/mm/vmemmap_dedup.rst @@ -24,7 +24,7 @@ For each base page, there is a corresponding ``struct page``. Within the HugeTLB subsystem, only the first 4 ``struct page`` are used to contain unique information about a HugeTLB page. ``__NR_USED_SUBPAGE`` provides this upper limit. The only 'useful' information in the remaining ``struct page`` -is the compound_head field, and this field is the same for all tail pages. +is the compound_info field, and this field is the same for all tail pages. By removing redundant ``struct page`` for HugeTLB pages, memory can be returned to the buddy allocator for other uses. @@ -124,10 +124,10 @@ Here is how things look before optimization:: | | +-----------+ -The value of page->compound_head is the same for all tail pages. The first +The value of page->compound_info is the same for all tail pages. The first page of ``struct page`` (page 0) associated with the HugeTLB page contains the 4 ``struct page`` necessary to describe the HugeTLB. The only use of the remaining -pages of ``struct page`` (page 1 to page 7) is to point to page->compound_head. +pages of ``struct page`` (page 1 to page 7) is to point to page->compound_info. Therefore, we can remap pages 1 to 7 to page 0. Only 1 page of ``struct page`` will be used for each HugeTLB page. This will allow us to free the remaining 7 pages to the buddy allocator. diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h index 90e5790c318f..a94683272869 100644 --- a/include/linux/mm_types.h +++ b/include/linux/mm_types.h @@ -125,14 +125,14 @@ struct page { atomic_long_t pp_ref_count; }; struct { /* Tail pages of compound page */ - unsigned long compound_head; /* Bit zero is set */ + unsigned long compound_info; /* Bit zero is set */ }; struct { /* ZONE_DEVICE pages */ /* - * The first word is used for compound_head or folio + * The first word is used for compound_info or folio * pgmap */ - void *_unused_pgmap_compound_head; + void *_unused_pgmap_compound_info; void *zone_device_data; /* * ZONE_DEVICE private pages are counted as being @@ -383,7 +383,7 @@ struct folio { /* private: avoid cluttering the output */ /* For the Unevictable "LRU list" slot */ struct { - /* Avoid compound_head */ + /* Avoid compound_info */ void *__filler; /* public: */ unsigned int mlock_count; @@ -484,7 +484,7 @@ struct folio { FOLIO_MATCH(flags, flags); FOLIO_MATCH(lru, lru); FOLIO_MATCH(mapping, mapping); -FOLIO_MATCH(compound_head, lru); +FOLIO_MATCH(compound_info, lru); FOLIO_MATCH(__folio_index, index); FOLIO_MATCH(private, private); FOLIO_MATCH(_mapcount, _mapcount); @@ -503,7 +503,7 @@ FOLIO_MATCH(_last_cpupid, _last_cpupid); static_assert(offsetof(struct folio, fl) == \ offsetof(struct page, pg) + sizeof(struct page)) FOLIO_MATCH(flags, _flags_1); -FOLIO_MATCH(compound_head, _head_1); +FOLIO_MATCH(compound_info, _head_1); FOLIO_MATCH(_mapcount, _mapcount_1); FOLIO_MATCH(_refcount, _refcount_1); #undef FOLIO_MATCH @@ -511,13 +511,13 @@ FOLIO_MATCH(_refcount, _refcount_1); static_assert(offsetof(struct folio, fl) == \ offsetof(struct page, pg) + 2 * sizeof(struct page)) FOLIO_MATCH(flags, _flags_2); -FOLIO_MATCH(compound_head, _head_2); +FOLIO_MATCH(compound_info, _head_2); #undef FOLIO_MATCH #define FOLIO_MATCH(pg, fl) \ static_assert(offsetof(struct folio, fl) == \ offsetof(struct page, pg) + 3 * sizeof(struct page)) FOLIO_MATCH(flags, _flags_3); -FOLIO_MATCH(compound_head, _head_3); +FOLIO_MATCH(compound_info, _head_3); #undef FOLIO_MATCH /** @@ -583,8 +583,8 @@ struct ptdesc { #define TABLE_MATCH(pg, pt) \ static_assert(offsetof(struct page, pg) == offsetof(struct ptdesc, pt)) TABLE_MATCH(flags, pt_flags); -TABLE_MATCH(compound_head, pt_list); -TABLE_MATCH(compound_head, _pt_pad_1); +TABLE_MATCH(compound_info, pt_list); +TABLE_MATCH(compound_info, _pt_pad_1); TABLE_MATCH(mapping, __page_mapping); TABLE_MATCH(__folio_index, pt_index); TABLE_MATCH(rcu_head, pt_rcu_head); diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h index 2c1153dd7e0e..446f89c01a4c 100644 --- a/include/linux/page-flags.h +++ b/include/linux/page-flags.h @@ -213,7 +213,7 @@ static __always_inline const struct page *page_fixed_fake_head(const struct page /* * Only addresses aligned with PAGE_SIZE of struct page may be fake head * struct page. The alignment check aims to avoid access the fields ( - * e.g. compound_head) of the @page[1]. It can avoid touch a (possibly) + * e.g. compound_info) of the @page[1]. It can avoid touch a (possibly) * cold cacheline in some cases. */ if (IS_ALIGNED((unsigned long)page, PAGE_SIZE) && @@ -223,7 +223,7 @@ static __always_inline const struct page *page_fixed_fake_head(const struct page * because the @page is a compound page composed with at least * two contiguous pages. */ - unsigned long head = READ_ONCE(page[1].compound_head); + unsigned long head = READ_ONCE(page[1].compound_info); if (likely(head & 1)) return (const struct page *)(head - 1); @@ -281,7 +281,7 @@ static __always_inline int page_is_fake_head(const struct page *page) static __always_inline unsigned long _compound_head(const struct page *page) { - unsigned long head = READ_ONCE(page->compound_head); + unsigned long head = READ_ONCE(page->compound_info); if (unlikely(head & 1)) return head - 1; @@ -320,13 +320,13 @@ static __always_inline unsigned long _compound_head(const struct page *page) static __always_inline int PageTail(const struct page *page) { - return READ_ONCE(page->compound_head) & 1 || page_is_fake_head(page); + return READ_ONCE(page->compound_info) & 1 || page_is_fake_head(page); } static __always_inline int PageCompound(const struct page *page) { return test_bit(PG_head, &page->flags.f) || - READ_ONCE(page->compound_head) & 1; + READ_ONCE(page->compound_info) & 1; } #define PAGE_POISON_PATTERN -1l @@ -348,7 +348,7 @@ static const unsigned long *const_folio_flags(const struct folio *folio, { const struct page *page = &folio->page; - VM_BUG_ON_PGFLAGS(page->compound_head & 1, page); + VM_BUG_ON_PGFLAGS(page->compound_info & 1, page); VM_BUG_ON_PGFLAGS(n > 0 && !test_bit(PG_head, &page->flags.f), page); return &page[n].flags.f; } @@ -357,7 +357,7 @@ static unsigned long *folio_flags(struct folio *folio, unsigned n) { struct page *page = &folio->page; - VM_BUG_ON_PGFLAGS(page->compound_head & 1, page); + VM_BUG_ON_PGFLAGS(page->compound_info & 1, page); VM_BUG_ON_PGFLAGS(n > 0 && !test_bit(PG_head, &page->flags.f), page); return &page[n].flags.f; } @@ -869,12 +869,12 @@ static __always_inline void set_compound_head(struct page *page, struct page *head, unsigned int order) { - WRITE_ONCE(page->compound_head, (unsigned long)head + 1); + WRITE_ONCE(page->compound_info, (unsigned long)head + 1); } static __always_inline void clear_compound_head(struct page *page) { - WRITE_ONCE(page->compound_head, 0); + WRITE_ONCE(page->compound_info, 0); } #ifdef CONFIG_TRANSPARENT_HUGEPAGE diff --git a/include/linux/types.h b/include/linux/types.h index 6dfdb8e8e4c3..3a65f0ef4a73 100644 --- a/include/linux/types.h +++ b/include/linux/types.h @@ -234,7 +234,7 @@ struct ustat { * * This guarantee is important for few reasons: * - future call_rcu_lazy() will make use of lower bits in the pointer; - * - the structure shares storage space in struct page with @compound_head, + * - the structure shares storage space in struct page with @compound_info, * which encode PageTail() in bit 0. The guarantee is needed to avoid * false-positive PageTail(). */ diff --git a/kernel/vmcore_info.c b/kernel/vmcore_info.c index e066d31d08f8..782bc2050a40 100644 --- a/kernel/vmcore_info.c +++ b/kernel/vmcore_info.c @@ -175,7 +175,7 @@ static int __init crash_save_vmcoreinfo_init(void) VMCOREINFO_OFFSET(page, lru); VMCOREINFO_OFFSET(page, _mapcount); VMCOREINFO_OFFSET(page, private); - VMCOREINFO_OFFSET(page, compound_head); + VMCOREINFO_OFFSET(page, compound_info); VMCOREINFO_OFFSET(pglist_data, node_zones); VMCOREINFO_OFFSET(pglist_data, nr_zones); #ifdef CONFIG_FLATMEM diff --git a/mm/page_alloc.c b/mm/page_alloc.c index fe77c00c99df..cecd6d89ff60 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -704,7 +704,7 @@ static inline bool pcp_allowed_order(unsigned int order) * The first PAGE_SIZE page is called the "head page" and have PG_head set. * * The remaining PAGE_SIZE pages are called "tail pages". PageTail() is encoded - * in bit 0 of page->compound_head. The rest of bits is pointer to head page. + * in bit 0 of page->compound_info. The rest of bits is pointer to head page. * * The first tail page's ->compound_order holds the order of allocation. * This usage means that zero-order pages may not be compound. diff --git a/mm/slab.h b/mm/slab.h index 078daecc7cf5..b471877af296 100644 --- a/mm/slab.h +++ b/mm/slab.h @@ -104,7 +104,7 @@ struct slab { #define SLAB_MATCH(pg, sl) \ static_assert(offsetof(struct page, pg) == offsetof(struct slab, sl)) SLAB_MATCH(flags, flags); -SLAB_MATCH(compound_head, slab_cache); /* Ensure bit 0 is clear */ +SLAB_MATCH(compound_info, slab_cache); /* Ensure bit 0 is clear */ SLAB_MATCH(_refcount, __page_refcount); #ifdef CONFIG_MEMCG SLAB_MATCH(memcg_data, obj_exts); diff --git a/mm/util.c b/mm/util.c index 8989d5767528..cbf93cf3223a 100644 --- a/mm/util.c +++ b/mm/util.c @@ -1244,7 +1244,7 @@ void snapshot_page(struct page_snapshot *ps, const struct page *page) again: memset(&ps->folio_snapshot, 0, sizeof(struct folio)); memcpy(&ps->page_snapshot, page, sizeof(*page)); - head = ps->page_snapshot.compound_head; + head = ps->page_snapshot.compound_info; if ((head & 1) == 0) { ps->idx = 0; foliop = (struct folio *)&ps->page_snapshot; -- 2.51.2