On Fri, Jun 09, 2023 at 02:32:57PM +0200, Vlastimil Babka wrote:

On 5/31/23 17:48, Catalin Marinas wrote:

quoted

diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h
index 0ee20b764000..3288a1339271 100644
--- a/include/linux/dma-mapping.h
+++ b/include/linux/dma-mapping.h

@@ -545,7 +545,7 @@ static inline int dma_set_min_align_mask(struct device *dev,
 
 static inline int dma_get_cache_alignment(void)
 {
-#ifdef ARCH_DMA_MINALIGN
+#ifdef ARCH_HAS_DMA_MINALIGN
 	return ARCH_DMA_MINALIGN;
 #endif
 	return 1;

diff --git a/include/linux/slab.h b/include/linux/slab.h
index 6b3e155b70bf..50dcf9cfbf62 100644
--- a/include/linux/slab.h
+++ b/include/linux/slab.h

@@ -235,12 +235,20 @@ void kmem_dump_obj(void *object);
  * alignment larger than the alignment of a 64-bit integer.
  * Setting ARCH_DMA_MINALIGN in arch headers allows that.
  */
-#if defined(ARCH_DMA_MINALIGN) && ARCH_DMA_MINALIGN > 8
+#ifdef ARCH_DMA_MINALIGN
+#define ARCH_HAS_DMA_MINALIGN
+#if ARCH_DMA_MINALIGN > 8 && !defined(ARCH_KMALLOC_MINALIGN)
 #define ARCH_KMALLOC_MINALIGN ARCH_DMA_MINALIGN
-#define KMALLOC_MIN_SIZE ARCH_DMA_MINALIGN
-#define KMALLOC_SHIFT_LOW ilog2(ARCH_DMA_MINALIGN)
+#endif
 #else
+#define ARCH_DMA_MINALIGN __alignof__(unsigned long long)
+#endif

It seems weird to make slab.h responsible for this part, especially for
#define ARCH_HAS_DMA_MINALIGN, which dma-mapping.h consumes. Maybe it would
be difficult to do differently due to some dependency hell, but minimally I
don't see dma-mapping.h including slab.h so the result is
include-order-dependent? Maybe it's included transitively, but then it's
fragile and would be better to do explicitly?

True, there's a risk that it doesn't get included with some future
header refactoring.

What about moving ARCH_DMA_MINALIGN to linux/cache.h? Alternatively, I
could create a new linux/dma-minalign.h file but I feel since this is
about caches, having it in cache.h makes more sense. asm/cache.h is also
where most archs define the constant (apart from mips, sh, microblaze).

-- 
Catalin

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