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[2003:cb:c734:9600:af27:4326:a216:2bfb]) by smtp.gmail.com with UTF8SMTPSA id ffacd0b85a97d-390e47a7b88sm14820945f8f.40.2025.03.03.08.30.24 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 03 Mar 2025 08:30:25 -0800 (PST) From: David Hildenbrand To: linux-kernel@vger.kernel.org Cc: linux-doc@vger.kernel.org, cgroups@vger.kernel.org, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-api@vger.kernel.org, David Hildenbrand , Andrew Morton , "Matthew Wilcox (Oracle)" , Tejun Heo , Zefan Li , Johannes Weiner , =?UTF-8?q?Michal=20Koutn=C3=BD?= , Jonathan Corbet , Andy Lutomirski , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , Muchun Song , "Liam R. Howlett" , Lorenzo Stoakes , Vlastimil Babka , Jann Horn Subject: [PATCH v3 04/20] mm: move hugetlb specific things in folio to page[3] Date: Mon, 3 Mar 2025 17:29:57 +0100 Message-ID: <20250303163014.1128035-5-david@redhat.com> X-Mailer: git-send-email 2.48.1 In-Reply-To: <20250303163014.1128035-1-david@redhat.com> References: <20250303163014.1128035-1-david@redhat.com> Precedence: bulk X-Mailing-List: linux-api@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Let's just move the hugetlb specific stuff to a separate page, and stop letting it overlay other fields for now. This frees up some space in page[2], which we will use on 32bit to free up some space in page[1]. While we could move these things to page[3] instead, it's cleaner to just move the hugetlb specific things out of the way and pack the core-folio stuff as tight as possible. ... and we can minimize the work required in dump_folio. We can now avoid re-initializing &folio->_deferred_list in hugetlb code. Hopefully dynamically allocating "strut folio" in the future will further clean this up. Signed-off-by: David Hildenbrand --- include/linux/mm_types.h | 27 +++++++++++++++++---------- mm/hugetlb.c | 1 - mm/page_alloc.c | 5 +++++ 3 files changed, 22 insertions(+), 11 deletions(-) diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h index e81be20bbabc6..1d9c68c551d42 100644 --- a/include/linux/mm_types.h +++ b/include/linux/mm_types.h @@ -405,20 +405,23 @@ struct folio { unsigned long _flags_2; unsigned long _head_2; /* public: */ - void *_hugetlb_subpool; - void *_hugetlb_cgroup; - void *_hugetlb_cgroup_rsvd; - void *_hugetlb_hwpoison; + struct list_head _deferred_list; /* private: the union with struct page is transitional */ }; + struct page __page_2; + }; + union { struct { - unsigned long _flags_2a; - unsigned long _head_2a; + unsigned long _flags_3; + unsigned long _head_3; /* public: */ - struct list_head _deferred_list; + void *_hugetlb_subpool; + void *_hugetlb_cgroup; + void *_hugetlb_cgroup_rsvd; + void *_hugetlb_hwpoison; /* private: the union with struct page is transitional */ }; - struct page __page_2; + struct page __page_3; }; }; @@ -455,8 +458,12 @@ FOLIO_MATCH(_refcount, _refcount_1); offsetof(struct page, pg) + 2 * sizeof(struct page)) FOLIO_MATCH(flags, _flags_2); FOLIO_MATCH(compound_head, _head_2); -FOLIO_MATCH(flags, _flags_2a); -FOLIO_MATCH(compound_head, _head_2a); +#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); #undef FOLIO_MATCH /** diff --git a/mm/hugetlb.c b/mm/hugetlb.c index 70a012af4a8d2..c15723c8d5e7f 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -1634,7 +1634,6 @@ static void __update_and_free_hugetlb_folio(struct hstate *h, folio_ref_unfreeze(folio, 1); - INIT_LIST_HEAD(&folio->_deferred_list); hugetlb_free_folio(folio); } diff --git a/mm/page_alloc.c b/mm/page_alloc.c index ae0f2a2e87369..2fc03cb13e49d 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -975,6 +975,11 @@ static int free_tail_page_prepare(struct page *head_page, struct page *page) goto out; } break; + case 3: + /* the third tail page: hugetlb specifics overlap ->mappings */ + if (IS_ENABLED(CONFIG_HUGETLB_PAGE)) + break; + fallthrough; default: if (page->mapping != TAIL_MAPPING) { bad_page(page, "corrupted mapping in tail page"); -- 2.48.1