[PATCH v4 14/15] mm: slab: Reduce the kmalloc() minimum alignment if DMA bouncing possible

[Catalin Marinas]

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>
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 | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/mm/slab_common.c b/mm/slab_common.c
index 7c6475847fdf..84e5a5e435d6 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>
@@ -865,7 +866,13 @@ void __init setup_kmalloc_cache_index_table(void)
 
 static unsigned int __kmalloc_minalign(void)
 {
-	return dma_get_cache_alignment();
+	int cache_align = dma_get_cache_alignment();
+
+	if (!IS_ENABLED(CONFIG_DMA_BOUNCE_UNALIGNED_KMALLOC) ||
+	    io_tlb_default_mem.nslabs == 0)
+		return cache_align;
+
+	return ARCH_KMALLOC_MINALIGN;
 }
 
 void __init