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Subject[PATCH 1/1] swiotlb: dump used and total slots when swiotlb buffer is full
So far the kernel only prints the requested size if swiotlb buffer if full.
It is not possible to know whether it is simply an out of buffer, or it is
because swiotlb cannot allocate buffer with the requested size due to

As 'io_tlb_used' is available since commit 71602fe6d4e9 ("swiotlb: add
debugfs to track swiotlb buffer usage"), both 'io_tlb_used' and
'io_tlb_nslabs' are printed when swiotlb buffer is full.

Signed-off-by: Dongli Zhang <>
kernel/dma/swiotlb.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c
index 53012db..3f43b37 100644
--- a/kernel/dma/swiotlb.c
+++ b/kernel/dma/swiotlb.c
@@ -540,7 +540,8 @@ phys_addr_t swiotlb_tbl_map_single(struct device *hwdev,
spin_unlock_irqrestore(&io_tlb_lock, flags);
if (!(attrs & DMA_ATTR_NO_WARN) && printk_ratelimit())
- dev_warn(hwdev, "swiotlb buffer is full (sz: %zd bytes)\n", size);
+ dev_warn(hwdev, "swiotlb buffer is full (sz: %zd bytes), total %lu, used %lu\n",
+ size, io_tlb_nslabs, io_tlb_used);
io_tlb_used += nslots;
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