From 8b0977ecc8b30a30966e76fcb64cef5041626b02 Mon Sep 17 00:00:00 2001 From: Michael Kelley Date: Thu, 13 Apr 2023 10:57:37 -0700 Subject: swiotlb: track and report io_tlb_used high water marks in debugfs swiotlb currently reports the total number of slabs and the instantaneous in-use slabs in debugfs. But with increased usage of swiotlb for all I/O in Confidential Computing (coco) VMs, it has become difficult to know how much memory to allocate for swiotlb bounce buffers, either via the automatic algorithm in the kernel or by specifying a value on the kernel boot line. The current automatic algorithm generously allocates swiotlb bounce buffer memory, and may be wasting significant memory in many use cases. To support better understanding of swiotlb usage, add tracking of the the high water mark for usage of the default swiotlb bounce buffer memory pool and any reserved memory pools. Report these high water marks in debugfs along with the other swiotlb pool metrics. Allow the high water marks to be reset to zero at runtime by writing to them. Signed-off-by: Michael Kelley Signed-off-by: Christoph Hellwig --- include/linux/swiotlb.h | 7 +++++++ 1 file changed, 7 insertions(+) (limited to 'include/linux/swiotlb.h') diff --git a/include/linux/swiotlb.h b/include/linux/swiotlb.h index bcef10e20ea4..6dc4598d2260 100644 --- a/include/linux/swiotlb.h +++ b/include/linux/swiotlb.h @@ -87,6 +87,11 @@ dma_addr_t swiotlb_map(struct device *dev, phys_addr_t phys, * @for_alloc: %true if the pool is used for memory allocation * @nareas: The area number in the pool. * @area_nslabs: The slot number in the area. + * @total_used: The total number of slots in the pool that are currently used + * across all areas. Used only for calculating used_hiwater in + * debugfs. + * @used_hiwater: The high water mark for total_used. Used only for reporting + * in debugfs. */ struct io_tlb_mem { phys_addr_t start; @@ -102,6 +107,8 @@ struct io_tlb_mem { unsigned int area_nslabs; struct io_tlb_area *areas; struct io_tlb_slot *slots; + atomic_long_t total_used; + atomic_long_t used_hiwater; }; extern struct io_tlb_mem io_tlb_default_mem; -- cgit From ec274aff21b6a94c7973384ca80a503c1bc3b173 Mon Sep 17 00:00:00 2001 From: Petr Tesarik Date: Thu, 20 Apr 2023 11:58:58 +0200 Subject: swiotlb: Omit total_used and used_hiwater if !CONFIG_DEBUG_FS The tracking of used_hiwater adds an atomic operation to the hot path. This is acceptable only when debugging the kernel. To make sure that the fields can never be used by mistake, do not even include them in struct io_tlb_mem if CONFIG_DEBUG_FS is not set. The build fails after doing that. To fix it, it is necessary to remove all code specific to debugfs and instead provide a stub implementation of swiotlb_create_debugfs_files(). As a bonus, this change allows to remove one __maybe_unused attribute. Signed-off-by: Petr Tesarik Signed-off-by: Christoph Hellwig --- include/linux/swiotlb.h | 2 ++ kernel/dma/swiotlb.c | 15 ++++++++++++--- 2 files changed, 14 insertions(+), 3 deletions(-) (limited to 'include/linux/swiotlb.h') diff --git a/include/linux/swiotlb.h b/include/linux/swiotlb.h index 6dc4598d2260..44767844e12b 100644 --- a/include/linux/swiotlb.h +++ b/include/linux/swiotlb.h @@ -107,8 +107,10 @@ struct io_tlb_mem { unsigned int area_nslabs; struct io_tlb_area *areas; struct io_tlb_slot *slots; +#ifdef CONFIG_DEBUG_FS atomic_long_t total_used; atomic_long_t used_hiwater; +#endif }; extern struct io_tlb_mem io_tlb_default_mem; diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c index 9bbc2802a444..e67dafc255f2 100644 --- a/kernel/dma/swiotlb.c +++ b/kernel/dma/swiotlb.c @@ -966,6 +966,8 @@ bool is_swiotlb_active(struct device *dev) } EXPORT_SYMBOL_GPL(is_swiotlb_active); +#ifdef CONFIG_DEBUG_FS + static int io_tlb_used_get(void *data, u64 *val) { struct io_tlb_mem *mem = data; @@ -1015,15 +1017,22 @@ static void swiotlb_create_debugfs_files(struct io_tlb_mem *mem, &fops_io_tlb_hiwater); } -static int __init __maybe_unused swiotlb_create_default_debugfs(void) +static int __init swiotlb_create_default_debugfs(void) { swiotlb_create_debugfs_files(&io_tlb_default_mem, "swiotlb"); return 0; } -#ifdef CONFIG_DEBUG_FS late_initcall(swiotlb_create_default_debugfs); -#endif + +#else /* !CONFIG_DEBUG_FS */ + +static inline void swiotlb_create_debugfs_files(struct io_tlb_mem *mem, + const char *dirname) +{ +} + +#endif /* CONFIG_DEBUG_FS */ #ifdef CONFIG_DMA_RESTRICTED_POOL -- cgit