Some functions which take a struct page as an argument operate on PAGE_SIZE bytes. Others operate on the entire compound page if passed either a head or tail page. Others operate on the compound page if passed a head page, but PAGE_SIZE bytes if passed a tail page. Yet others either BUG or do the wrong thing if passed a tail page. This patch series starts to resolve this ambiguity by introducing a new type, the struct folio. A function which takes a struct folio argument declares that it will operate on the entire page. In return, the caller guarantees that the pointer it is passing does not point to a tail page. This allows us to do less work. Now we have a type that is guaranteed not to be a tail page, we can avoid calling compound_head(). That saves us hundreds of bytes of text and even manages to reduce the amount of data in the kernel image somehow. The focus for this patch series is on introducing infrastructure. The big correctness proof that exists in this patch series is to make it clear that one cannot wait (for the page lock or writeback) on a tail page. I don't believe there were any places which could miss a wakeup due to this, but it's hard to prove that without struct folio. Now the compiler proves it for us. v3: - Rebase on next-20210127. Two major sources of conflict, the generic_file_buffered_read refactoring (in akpm tree) and the fscache work (in dhowells tree). Not sure how this patch series can get merged with these two sources of conflict? v2: - Pare patch series back to just infrastructure and the page waiting parts. Matthew Wilcox (Oracle) (25): mm: Introduce struct folio mm: Add folio_pgdat mm/vmstat: Add folio stat wrappers mm/debug: Add VM_BUG_ON_FOLIO and VM_WARN_ON_ONCE_FOLIO mm: Add put_folio mm: Add get_folio mm: Create FolioFlags mm: Handle per-folio private data mm: Add folio_index, folio_page and folio_contains mm/util: Add folio_mapping and folio_file_mapping mm/memcg: Add folio_memcg, lock_folio_memcg and unlock_folio_memcg mm/memcg: Add mem_cgroup_folio_lruvec mm: Add unlock_folio mm: Add lock_folio mm: Add lock_folio_killable mm: Convert lock_page_async to lock_folio_async mm/filemap: Convert end_page_writeback to end_folio_writeback mm: Convert wait_on_page_bit to wait_on_folio_bit mm: Add wait_for_stable_folio and wait_on_folio_writeback mm: Add wait_on_folio_locked & wait_on_folio_locked_killable mm: Convert lock_page_or_retry to lock_folio_or_retry mm/filemap: Convert wake_up_page_bit to wake_up_folio_bit mm: Convert test_clear_page_writeback to test_clear_folio_writeback mm/filemap: Convert page wait queues to be folios cachefiles: Switch to wait_page_key fs/afs/write.c | 31 +++--- fs/cachefiles/rdwr.c | 13 ++- fs/io_uring.c | 2 +- include/linux/memcontrol.h | 22 ++++ include/linux/mm.h | 88 ++++++++++++---- include/linux/mm_types.h | 33 ++++++ include/linux/mmdebug.h | 20 ++++ include/linux/netfs.h | 5 + include/linux/page-flags.h | 106 +++++++++++++++---- include/linux/pagemap.h | 201 ++++++++++++++++++++++++----------- include/linux/vmstat.h | 60 +++++++++++ mm/filemap.c | 207 ++++++++++++++++++------------------- mm/memcontrol.c | 36 ++++--- mm/memory.c | 10 +- mm/page-writeback.c | 48 ++++----- mm/swapfile.c | 6 +- mm/util.c | 20 ++-- 17 files changed, 621 insertions(+), 287 deletions(-) -- 2.29.2
