dma-mapping: warn when coherent pool is depleted

When a DMA coherent pool is depleted, allocation failures may or may not get reported in the kernel log depending on the allocator. The admin does have a workaround, however, by using coherent_pool= on the kernel command line. Provide some guidance on the failure and a recommended minimum size for the pools (double the size). Signed-off-by: David Rientjes <[email protected]> Tested-by: Guenter Roeck <[email protected]> Signed-off-by: Christoph Hellwig <[email protected]>
josf · Jun 29, 2020 · 71cdec4 · 71cdec4
1 parent 9ebcfad
commit 71cdec4
Showing 1 changed file with 5 additions and 1 deletion.
diff --git a/kernel/dma/pool.c b/kernel/dma/pool.c
@@ -239,12 +239,16 @@ void *dma_alloc_from_pool(struct device *dev, size_t size,
 	}
 
 	val = gen_pool_alloc(pool, size);
-	if (val) {
+	if (likely(val)) {
 		phys_addr_t phys = gen_pool_virt_to_phys(pool, val);
 
 		*ret_page = pfn_to_page(__phys_to_pfn(phys));
 		ptr = (void *)val;
 		memset(ptr, 0, size);
+	} else {
+		WARN_ONCE(1, "DMA coherent pool depleted, increase size "
+			     "(recommended min coherent_pool=%zuK)\n",
+			  gen_pool_size(pool) >> 9);
 	}
 	if (gen_pool_avail(pool) < atomic_pool_size)
 		schedule_work(&atomic_pool_work);