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generic: 6.6: backport arm64 swiotlb default size reduction 

Kernel 6.6 added dynamic SWIOTLB allocation, but with it also started
allocating 64MB of the SWIOTLB bounce buffer by default which is quite a
lot of memory on most OpenWrt devices.

Luckily in kernel 6.7 arm64 received an optimization that reduces that
default size to 1MB per 1GB of RAM if certain criteria was met.

So in order to reclaim back 63MB of RAM which brought some ipq807x devices
close to OOM under load lets backport the upstream commit.

Signed-off-by: Robert Marko <robimarko@gmail.com>
This commit is contained in:
Robert Marko 2024-04-06 23:08:03 +02:00
parent 1ea6ddacc2
commit 153c9f3482
1 changed files with 51 additions and 0 deletions
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51
target/linux/generic/backport-6.6/300-v6.7-arm64-swiotlb-Reduce-the-default-size-if-no-ZONE_DMA.patch Normal file
View File

@ -0,0 +1,51 @@
From 65033574ade97afccba074d837fd269903a83a9a Mon Sep 17 00:00:00 2001
From: Catalin Marinas <catalin.marinas@arm.com>
Date: Thu, 5 Oct 2023 16:40:30 +0100
Subject: [PATCH] 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: 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>
---
arch/arm64/mm/init.c | 11 ++++++++++-
1 file changed, 10 insertions(+), 1 deletion(-)
--- a/arch/arm64/mm/init.c
+++ b/arch/arm64/mm/init.c
@@ -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);