[PATCH v6 16/17] mm: slab: Reduce the kmalloc() minimum alignment if DMA bouncing possible

[Vlastimil Babka]

On 5/31/23 17:48, Catalin Marinas wrote:
> If an architecture opted in to DMA bouncing of unaligned kmalloc()
> buffers (ARCH_WANT_KMALLOC_DMA_BOUNCE), reduce the minimum kmalloc()
> cache alignment below cache-line size to ARCH_KMALLOC_MINALIGN.
> 
> Signed-off-by: Catalin Marinas <catalin.marinas at arm.com>

Reviewed-by: Vlastimil Babka <vbabka at suse.cz>

Nit below:

> Cc: Andrew Morton <akpm at linux-foundation.org>
> Cc: Christoph Hellwig <hch at lst.de>
> Cc: Robin Murphy <robin.murphy at arm.com>
> ---
>  mm/slab_common.c | 10 ++++++++++
>  1 file changed, 10 insertions(+)
> 
> diff --git a/mm/slab_common.c b/mm/slab_common.c
> index 7c6475847fdf..fe46459a8b77 100644
> --- a/mm/slab_common.c
> +++ b/mm/slab_common.c
> @@ -18,6 +18,7 @@
>  #include <linux/uaccess.h>
>  #include <linux/seq_file.h>
>  #include <linux/dma-mapping.h>
> +#include <linux/swiotlb.h>
>  #include <linux/proc_fs.h>
>  #include <linux/debugfs.h>
>  #include <linux/kasan.h>
> @@ -863,10 +864,19 @@ void __init setup_kmalloc_cache_index_table(void)
>  	}
>  }
>  
> +#ifdef CONFIG_DMA_BOUNCE_UNALIGNED_KMALLOC
> +static unsigned int __kmalloc_minalign(void)
> +{
> +	if (io_tlb_default_mem.nslabs)
> +		return ARCH_KMALLOC_MINALIGN;
> +	return dma_get_cache_alignment();
> +}
> +#else
>  static unsigned int __kmalloc_minalign(void)
>  {
>  	return dma_get_cache_alignment();
>  }
> +#endif

Should be enough to put the #ifdef around the two lines into a single
implementation of the function?

>  void __init
>  new_kmalloc_cache(int idx, enum kmalloc_cache_type type, slab_flags_t flags)
>