Re: [PATCH v5 00/15] mm, dma, arm64: Reduce ARCH_KMALLOC_MINALIGN to 8

[Jonathan Cameron <Jonathan.Cameron@Huawei.com>]

On Wed, 24 May 2023 18:18:49 +0100
Catalin Marinas <catalin.marinas@arm.com> wrote:

> Hi,
> 
> Another version of the series reducing the kmalloc() minimum alignment
> on arm64 to 8 (from 128). Other architectures can easily opt in by
> defining ARCH_KMALLOC_MINALIGN as 8 and selecting
> DMA_BOUNCE_UNALIGNED_KMALLOC.
> 
> The first 10 patches decouple ARCH_KMALLOC_MINALIGN from
> ARCH_DMA_MINALIGN and, for arm64, limit the kmalloc() caches to those
> aligned to the run-time probed cache_line_size(). On arm64 we gain the
> kmalloc-{64,192} caches.
> 
> The subsequent patches (11 to 15) further reduce the kmalloc() caches to
> kmalloc-{8,16,32,96} if the default swiotlb is present by bouncing small
> buffers in the DMA API.

Hi Catalin,

I think IIO_DMA_MINALIGN needs to switch to ARCH_DMA_MINALIGN as well.

It's used to force static alignement of buffers with larger structures,
to make them suitable for non coherent DMA, similar to your other cases.

Thanks,

Jonathan


> 
> Changes since v4:
> 
> - Following Robin's suggestions, reworked the iommu handling so that the
>   buffer size checks are done in the dev_use_swiotlb() and
>   dev_use_sg_swiotlb() functions (together with dev_is_untrusted()). The
>   sync operations can now check for the SG_DMA_USE_SWIOTLB flag. Since
>   this flag is no longer specific to kmalloc() bouncing (covers
>   dev_is_untrusted() as well), the sg_is_dma_use_swiotlb() and
>   sg_dma_mark_use_swiotlb() functions are always defined if
>   CONFIG_SWIOTLB.
> 
> - Dropped ARCH_WANT_KMALLOC_DMA_BOUNCE, only left the
>   DMA_BOUNCE_UNALIGNED_KMALLOC option, selectable by the arch code. The
>   NEED_SG_DMA_FLAGS is now selected by IOMMU_DMA if SWIOTLB.
> 
> - Rather than adding another config option, allow
>   dma_get_cache_alignment() to be overridden by the arch code
>   (Christoph's suggestion).
> 
> - Added a comment to the dma_kmalloc_needs_bounce() function on the
>   heuristics behind the bouncing.
> 
> - Added acked-by/reviewed-by tags (not adding Ard's tested-by yet as
>   there were some changes).
> 
> The updated patches are also available on this branch:
> 
> git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux devel/kmalloc-minalign
> 
> Thanks.
> 
> Catalin Marinas (14):
>   mm/slab: Decouple ARCH_KMALLOC_MINALIGN from ARCH_DMA_MINALIGN
>   dma: Allow dma_get_cache_alignment() to be overridden by the arch code
>   mm/slab: Simplify create_kmalloc_cache() args and make it static
>   mm/slab: Limit kmalloc() minimum alignment to
>     dma_get_cache_alignment()
>   drivers/base: Use ARCH_DMA_MINALIGN instead of ARCH_KMALLOC_MINALIGN
>   drivers/gpu: Use ARCH_DMA_MINALIGN instead of ARCH_KMALLOC_MINALIGN
>   drivers/usb: Use ARCH_DMA_MINALIGN instead of ARCH_KMALLOC_MINALIGN
>   drivers/spi: Use ARCH_DMA_MINALIGN instead of ARCH_KMALLOC_MINALIGN
>   drivers/md: Use ARCH_DMA_MINALIGN instead of ARCH_KMALLOC_MINALIGN
>   arm64: Allow kmalloc() caches aligned to the smaller cache_line_size()
>   dma-mapping: Force bouncing if the kmalloc() size is not
>     cache-line-aligned
>   iommu/dma: Force bouncing if the size is not cacheline-aligned
>   mm: slab: Reduce the kmalloc() minimum alignment if DMA bouncing
>     possible
>   arm64: Enable ARCH_WANT_KMALLOC_DMA_BOUNCE for arm64
> 
> Robin Murphy (1):
>   scatterlist: Add dedicated config for DMA flags
> 
>  arch/arm64/Kconfig             |  1 +
>  arch/arm64/include/asm/cache.h |  3 ++
>  arch/arm64/mm/init.c           |  7 +++-
>  drivers/base/devres.c          |  6 ++--
>  drivers/gpu/drm/drm_managed.c  |  6 ++--
>  drivers/iommu/Kconfig          |  1 +
>  drivers/iommu/dma-iommu.c      | 50 +++++++++++++++++++++++-----
>  drivers/md/dm-crypt.c          |  2 +-
>  drivers/pci/Kconfig            |  1 +
>  drivers/spi/spidev.c           |  2 +-
>  drivers/usb/core/buffer.c      |  8 ++---
>  include/linux/dma-map-ops.h    | 61 ++++++++++++++++++++++++++++++++++
>  include/linux/dma-mapping.h    |  4 ++-
>  include/linux/scatterlist.h    | 29 +++++++++++++---
>  include/linux/slab.h           | 14 ++++++--
>  kernel/dma/Kconfig             |  7 ++++
>  kernel/dma/direct.h            |  3 +-
>  mm/slab.c                      |  6 +---
>  mm/slab.h                      |  5 ++-
>  mm/slab_common.c               | 46 +++++++++++++++++++------
>  20 files changed, 213 insertions(+), 49 deletions(-)
> 
> 
>