Commit 65033574 authored by Catalin Marinas's avatar Catalin Marinas
Browse files

arm64: swiotlb: Reduce the default size if no ZONE_DMA bouncing needed 



With CONFIG_DMA_BOUNCE_UNALIGNED_KMALLOC enabled, the arm64 kernel still
allocates the default SWIOTLB buffer (64MB) even if ZONE_DMA is disabled
or all the RAM fits into this zone. However, this potentially wastes a
non-negligible amount of memory on platforms with little RAM.

Reduce the SWIOTLB size to 1MB per 1GB of RAM if only needed for
kmalloc() buffer bouncing.

Signed-off-by: default avatarCatalin Marinas <catalin.marinas@arm.com>
Suggested-by: default avatarRoss Burton <ross.burton@arm.com>
Cc: Ross Burton <ross.burton@arm.com>
Cc: Will Deacon <will@kernel.org>
Reviewed-by: default avatarRobin Murphy <robin.murphy@arm.com>
parent 6465e260

arch/arm64/mm/init.c

+10 −1
Original line number Diff line number Diff line
@@ -16,6 +16,7 @@ 
#include <linux/nodemask.h>

#include <linux/initrd.h>

#include <linux/gfp.h>

#include <linux/math.h>

#include <linux/memblock.h>

#include <linux/sort.h>

#include <linux/of.h>
@@ -493,8 +494,16 @@ void __init mem_init(void) 
{

	bool swiotlb = max_pfn > PFN_DOWN(arm64_dma_phys_limit);



	if (IS_ENABLED(CONFIG_DMA_BOUNCE_UNALIGNED_KMALLOC))

	if (IS_ENABLED(CONFIG_DMA_BOUNCE_UNALIGNED_KMALLOC) && !swiotlb) {

		/*

		 * If no bouncing needed for ZONE_DMA, reduce the swiotlb

		 * buffer for kmalloc() bouncing to 1MB per 1GB of RAM.

		 */

		unsigned long size =

			DIV_ROUND_UP(memblock_phys_mem_size(), 1024);

		swiotlb_adjust_size(min(swiotlb_size_or_default(), size));

		swiotlb = true;

	}



	swiotlb_init(swiotlb, SWIOTLB_VERBOSE);