Hi, This RFC patch series attempts to support large folios for tmpfs. The first patch is based on Daniel's previous patches in [1], mainly using the length in the write and fallocate paths to get a highest order hint for large order allocation. The last patch adds mTHP filter control for tmpfs if mTHP is set for the following reasons: 1. Maintain backward compatibility for the control interface. Tmpfs already has a global 'huge=' mount option and '/sys/kernel/mm/transparent_hugepage/shmem_enabled' interface to control large order allocations. mTHP extends this capability to a per-size basis while maintaining good interface compatibility. 2. For the large order allocation of writable mmap() faults in tmpfs, we need something like the mTHP interfaces to control large orders, as well as ensuring consistent interfaces with shmem. 3. Ryan pointed out that large order allocations based on write length could lead to memory fragmentation issue. Just quoting Ryan's comment [2]: "And it's possible (likely even, in my opinion) that allocating lots of different folio sizes will exacerbate memory fragmentation, leading to more order-0 fallbacks, which would hurt the overall system performance in the long run, vs restricting to a couple of folio sizes." 4. Some hardware preferences, such as for the ARM64 architecture, can better utilize the cont-pte feature to reduce TLB pressure and optimize performance with a 64K size folio. Using mTHP can better leverage these hardware advantages. Any comments and suggestions are appreciated. Thanks. [1] https://lore.kernel.org/all/20240515055719.32577-1-da.gomez@xxxxxxxxxxx/ [2] https://lore.kernel.org/all/e83e1687-3e3c-40d0-bf0e-225871647092@xxxxxxx/ Changes from RFC v1: - Drop patch 1. - Use 'write_end' to calculate the length in shmem_allowable_huge_orders(). - Update shmem_mapping_size_order() per Daniel. Baolin Wang (1): mm: shmem: use mTHP interface to control huge orders for tmpfs Daniel Gomez (1): mm: shmem: add large folio support to the write and fallocate paths mm/memory.c | 4 ++-- mm/shmem.c | 66 +++++++++++++++++++++++++++++++++++++++++++++-------- 2 files changed, 58 insertions(+), 12 deletions(-) -- 2.39.3
