Re: [PATCH v6 04/17] mm/slab: Limit kmalloc() minimum alignment to dma_get_cache_alignment()

[Vlastimil Babka <vbabka@suse.cz>]

On 5/31/23 17:48, Catalin Marinas wrote:
> Do not create kmalloc() caches which are not aligned to
> dma_get_cache_alignment(). There is no functional change since for
> current architectures defining ARCH_DMA_MINALIGN, ARCH_KMALLOC_MINALIGN
> equals ARCH_DMA_MINALIGN (and dma_get_cache_alignment()). On
> architectures without a specific ARCH_DMA_MINALIGN,
> dma_get_cache_alignment() is 1, so no change to the kmalloc() caches.
> 
> If an architecture selects ARCH_HAS_DMA_CACHE_LINE_SIZE (introduced
> previously), the kmalloc() caches will be aligned to a cache line size.

It this part leftover from a previous version?

> Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Christoph Hellwig <hch@lst.de>
> Cc: Robin Murphy <robin.murphy@arm.com>

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

> ---
>  mm/slab_common.c | 24 +++++++++++++++++++++---
>  1 file changed, 21 insertions(+), 3 deletions(-)
> 
> diff --git a/mm/slab_common.c b/mm/slab_common.c
> index 7f069159aee2..7c6475847fdf 100644
> --- a/mm/slab_common.c
> +++ b/mm/slab_common.c
> @@ -17,6 +17,7 @@
>  #include <linux/cpu.h>
>  #include <linux/uaccess.h>
>  #include <linux/seq_file.h>
> +#include <linux/dma-mapping.h>
>  #include <linux/proc_fs.h>
>  #include <linux/debugfs.h>
>  #include <linux/kasan.h>
> @@ -862,9 +863,18 @@ void __init setup_kmalloc_cache_index_table(void)
>  	}
>  }
>  
> +static unsigned int __kmalloc_minalign(void)
> +{
> +	return dma_get_cache_alignment();
> +}
> +
>  void __init
>  new_kmalloc_cache(int idx, enum kmalloc_cache_type type, slab_flags_t flags)
>  {
> +	unsigned int minalign = __kmalloc_minalign();
> +	unsigned int aligned_size = kmalloc_info[idx].size;
> +	int aligned_idx = idx;
> +
>  	if ((KMALLOC_RECLAIM != KMALLOC_NORMAL) && (type == KMALLOC_RECLAIM)) {
>  		flags |= SLAB_RECLAIM_ACCOUNT;
>  	} else if (IS_ENABLED(CONFIG_MEMCG_KMEM) && (type == KMALLOC_CGROUP)) {
> @@ -877,9 +887,17 @@ new_kmalloc_cache(int idx, enum kmalloc_cache_type type, slab_flags_t flags)
>  		flags |= SLAB_CACHE_DMA;
>  	}
>  
> -	kmalloc_caches[type][idx] = create_kmalloc_cache(
> -					kmalloc_info[idx].name[type],
> -					kmalloc_info[idx].size, flags);
> +	if (minalign > ARCH_KMALLOC_MINALIGN) {
> +		aligned_size = ALIGN(aligned_size, minalign);
> +		aligned_idx = __kmalloc_index(aligned_size, false);
> +	}
> +
> +	if (!kmalloc_caches[type][aligned_idx])
> +		kmalloc_caches[type][aligned_idx] = create_kmalloc_cache(
> +					kmalloc_info[aligned_idx].name[type],
> +					aligned_size, flags);
> +	if (idx != aligned_idx)
> +		kmalloc_caches[type][idx] = kmalloc_caches[type][aligned_idx];
>  
>  	/*
>  	 * If CONFIG_MEMCG_KMEM is enabled, disable cache merging for
>