From cbe298d82cf70aa6bb16cfc8ae4db522f39a0034 Mon Sep 17 00:00:00 2001 From: Alistair Popple Date: Fri, 28 Feb 2025 14:31:03 +1100 Subject: fs/dax: remove PAGE_MAPPING_DAX_SHARED mapping flag The page ->mapping pointer can have magic values like PAGE_MAPPING_DAX_SHARED and PAGE_MAPPING_ANON for page owner specific usage. Currently PAGE_MAPPING_DAX_SHARED and PAGE_MAPPING_ANON alias to the same value. This isn't a problem because FS DAX pages are never seen by the anonymous mapping code and vice versa. However a future change will make FS DAX pages more like normal pages, so folio_test_anon() must not return true for a FS DAX page. We could explicitly test for a FS DAX page in folio_test_anon(), etc. however the PAGE_MAPPING_DAX_SHARED flag isn't actually needed. Instead we can use the page->mapping field to implicitly track the first mapping of a page. If page->mapping is non-NULL it implies the page is associated with a single mapping at page->index. If the page is associated with a second mapping clear page->mapping and set page->share to 1. This is possible because a shared mapping implies the file-system implements dax_holder_operations which makes the ->mapping and ->index, which is a union with ->share, unused. The page is considered shared when page->mapping == NULL and page->share > 0 or page->mapping != NULL, implying it is present in at least one address space. This also makes it easier for a future change to detect when a page is first mapped into an address space which requires special handling. Link: https://lkml.kernel.org/r/c22f699202db0acee2f7039eb026e68261ce42d6.1740713401.git-series.apopple@nvidia.com Signed-off-by: Alistair Popple Tested-by: Alison Schofield Cc: Asahi Lina Cc: Bjorn Helgaas Cc: Catalin Marinas Cc: Christoph Hellwig Cc: Chunyan Zhang Cc: Dan Wiliams Cc: "Darrick J. Wong" Cc: Dave Chinner Cc: Dave Hansen Cc: Dave Jiang Cc: David Hildenbrand Cc: Gerald Schaefer Cc: Huacai Chen Cc: Ira Weiny Cc: Jan Kara Cc: Jason Gunthorpe Cc: John Hubbard Cc: linmiaohe Cc: Logan Gunthorpe Cc: Matthew Wilcow (Oracle) Cc: Michael "Camp Drill Sergeant" Ellerman Cc: Nicholas Piggin Cc: Peter Xu Cc: Ted Ts'o Cc: Vishal Verma Cc: WANG Xuerui Cc: Will Deacon Cc: Alexander Gordeev Cc: Balbir Singh Cc: Christian Borntraeger Cc: Heiko Carstens Cc: Jason Gunthorpe Cc: Sven Schnelle Cc: Vasily Gorbik Cc: Vivek Goyal Signed-off-by: Andrew Morton --- include/linux/page-flags.h | 6 ------ 1 file changed, 6 deletions(-) (limited to 'include') diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h index 36d283552f80..cab382bd965e 100644 --- a/include/linux/page-flags.h +++ b/include/linux/page-flags.h @@ -673,12 +673,6 @@ PAGEFLAG_FALSE(VmemmapSelfHosted, vmemmap_self_hosted) #define PAGE_MAPPING_KSM (PAGE_MAPPING_ANON | PAGE_MAPPING_MOVABLE) #define PAGE_MAPPING_FLAGS (PAGE_MAPPING_ANON | PAGE_MAPPING_MOVABLE) -/* - * Different with flags above, this flag is used only for fsdax mode. It - * indicates that this page->mapping is now under reflink case. - */ -#define PAGE_MAPPING_DAX_SHARED ((void *)0x1) - static __always_inline bool folio_mapping_flags(const struct folio *folio) { return ((unsigned long)folio->mapping & PAGE_MAPPING_FLAGS) != 0; -- cgit v1.2.3