On Thu, Apr 11, 2024 at 10:57:31AM +1000, Alistair Popple wrote: > The devmap PTE special bit was used to detect mappings of FS DAX > pages. This tracking was required to ensure the generic mm did not > manipulate the page reference counts as FS DAX implemented it's own > reference counting scheme. > > Now that FS DAX pages have their references counted the same way as > normal pages this tracking is no longer needed and can be > removed. > > Almost all existing uses of pmd_devmap() are paired with a check of > pmd_trans_huge(). As pmd_trans_huge() now returns true for FS DAX pages > dropping the check in these cases doesn't change anything. > > However care needs to be taken because pmd_trans_huge() also checks that > a page is not an FS DAX page. This is dealt with either by checking > !vma_is_dax() or relying on the fact that the page pointer was obtained > from a page list. This is possible because zone device pages cannot > appear in any page list due to sharing page->lru with page->pgmap. > > Signed-off-by: Alistair Popple <apopple@xxxxxxxxxx> > --- > Documentation/mm/arch_pgtable_helpers.rst | 6 +- > arch/arm64/include/asm/pgtable.h | 24 +--- > arch/powerpc/include/asm/book3s/64/pgtable.h | 42 +------ > arch/powerpc/mm/book3s64/hash_pgtable.c | 3 +- > arch/powerpc/mm/book3s64/pgtable.c | 8 +- > arch/powerpc/mm/book3s64/radix_pgtable.c | 5 +- > arch/powerpc/mm/pgtable.c | 2 +- > arch/x86/include/asm/pgtable.h | 31 +---- > fs/dax.c | 5 +- > fs/userfaultfd.c | 2 +- > include/linux/huge_mm.h | 10 +- > include/linux/mm.h | 7 +- > include/linux/pgtable.h | 17 +-- > mm/debug_vm_pgtable.c | 51 +------- > mm/gup.c | 151 +-------------------- > mm/hmm.c | 5 +- > mm/huge_memory.c | 100 +------------- > mm/khugepaged.c | 2 +- > mm/mapping_dirty_helpers.c | 4 +- > mm/memory.c | 25 +--- > mm/migrate_device.c | 2 +- > mm/mprotect.c | 2 +- > mm/mremap.c | 5 +- > mm/page_vma_mapped.c | 5 +- > mm/pgtable-generic.c | 7 +- > mm/vmscan.c | 5 +- > 26 files changed, 48 insertions(+), 478 deletions(-) This is great I suggest splitting it up into two parts, remove the functional code in the core mm calling these functions testing and setting pXX_devmap (and maybe this needs several patches for clarity) and then remove all the remaining dead code once all the callers are gone. Jason
