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

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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: Catalin Marinas <catalin.marinas@arm.com>
Suggested-by: Ross Burton <ross.burton@arm.com>
Cc: Ross Burton <ross.burton@arm.com>
Cc: Will Deacon <will@kernel.org>
Reviewed-by: Robin Murphy <robin.murphy@arm.com>
This commit is contained in:
Catalin Marinas 2023-10-05 16:40:30 +01:00
parent 6465e260f4
commit 65033574ad
1 changed files with 10 additions and 1 deletions
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11
arch/arm64/mm/init.c
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@ -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);