Hi, On arm64 ARCH_DMA_MINALIGN (and therefore ARCH_KMALLOC_MINALIGN) is 128. While the majority of arm64 SoCs have a 64-byte cache line size (or rather CWG - cache writeback granule), we chose a less than optimal value in order to support all SoCs in a single kernel image. The aim of this series is to allow smaller default ARCH_KMALLOC_MINALIGN with kmalloc() caches configured at boot time to be safe when an SoC has a larger DMA alignment requirement. The first patch decouples ARCH_KMALLOC_MINALIGN from ARCH_DMA_MINALIGN with the aim to only use the latter in DMA-specific compile-time annotations. ARCH_KMALLOC_MINALIGN becomes the minimum (static) guaranteed kmalloc() alignment but not necessarily safe for non-coherent DMA. Patches 2-7 change some drivers/ code to use ARCH_DMA_MINALIGN instead of ARCH_KMALLOC_MINALIGN. Patch 8 introduces the dynamic arch_kmalloc_minalign() and the slab code changes to set the corresponding minimum alignment on the newly created kmalloc() caches. Patch 10 defines arch_kmalloc_minalign() for arm64 returning cache_line_size() together with reducing ARCH_KMALLOC_MINALIGN to 64. ARCH_DMA_MINALIGN remains 128 on arm64. I don't have access to it but there's the Fujitsu A64FX with a CWG of 256 (the arm64 cache_line_size() returns 256). This series will bump the smallest kmalloc cache to kmalloc-256. The platform is known to be fully cache coherent (or so I think) and we decided long ago not to bump ARCH_DMA_MINALIGN to 256. If problematic, we could make the dynamic kmalloc() alignment on arm64 min(ARCH_DMA_MINALIGN, cache_line_size()). This series is beneficial to arm64 even if it's only reducing the kmalloc() minimum alignment to 64. While it would be nice to reduce this further to 8 (or 16) on SoCs known to be fully DMA coherent, detecting this is via arch_setup_dma_ops() is problematic, especially with late probed devices. I'd leave it for an additional RFC series on top of this (there are ideas like bounce buffering for non-coherent devices if the SoC was deemed coherent). Thanks. Catalin Marinas (10): mm/slab: Decouple ARCH_KMALLOC_MINALIGN from ARCH_DMA_MINALIGN drivers/base: Use ARCH_DMA_MINALIGN instead of ARCH_KMALLOC_MINALIGN drivers/gpu: Use ARCH_DMA_MINALIGN instead of ARCH_KMALLOC_MINALIGN drivers/md: Use ARCH_DMA_MINALIGN instead of ARCH_KMALLOC_MINALIGN drivers/spi: Use ARCH_DMA_MINALIGN instead of ARCH_KMALLOC_MINALIGN drivers/usb: Use ARCH_DMA_MINALIGN instead of ARCH_KMALLOC_MINALIGN crypto: Use ARCH_DMA_MINALIGN instead of ARCH_KMALLOC_MINALIGN mm/slab: Allow dynamic kmalloc() minimum alignment mm/slab: Simplify create_kmalloc_cache() args and make it static arm64: Enable dynamic kmalloc() minimum alignment arch/arm64/include/asm/cache.h | 1 + arch/arm64/kernel/cacheinfo.c | 7 ++++++ drivers/base/devres.c | 4 ++-- drivers/gpu/drm/drm_managed.c | 4 ++-- drivers/md/dm-crypt.c | 2 +- drivers/spi/spidev.c | 2 +- drivers/usb/core/buffer.c | 8 +++---- drivers/usb/misc/usbtest.c | 2 +- include/linux/crypto.h | 2 +- include/linux/slab.h | 25 ++++++++++++++++----- mm/slab.c | 6 +---- mm/slab.h | 5 ++--- mm/slab_common.c | 40 ++++++++++++++++++++++------------ 13 files changed, 69 insertions(+), 39 deletions(-)
