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 <petr.tesarik.ext@huawei.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>

diff --git a/include/linux/swiotlb.h b/include/linux/swiotlb.h
index 6dc4598d22604a336756d6fd2956c19fce6fd97e..44767844e12b123273e8b9510d80dd907fd7b985 100644 (file)
--- 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 9bbc2802a44475eaf9178f1018dc05586aa21f18..e67dafc255f2ca1543fa16b899f982f7611fc45a 100644 (file)
--- 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