[PATCH v3 04/20] mm: move hugetlb specific things in folio to page[3]
From: David Hildenbrand <hidden>
Date: 2025-03-03 16:30:29
Also in:
cgroups, linux-doc, linux-fsdevel, linux-mm, lkml
Subsystem:
hugetlb subsystem, memory management, memory management - core, memory management - page allocator, the rest · Maintainers:
Muchun Song, Oscar Salvador, Andrew Morton, David Hildenbrand, Vlastimil Babka, Linus Torvalds
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 <redacted> --- 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