mm: cma: use pr_err_ratelimited for CMA warning

If we did not reserve extra CMA memory, the log buffer can be easily
filled up by CMA failure warning when the devices calling
dmam_alloc_coherent() to alloc DMA memory.  Thus we can use
pr_err_ratelimited() instead to reduce the duplicate CMA warning.

Link: https://lkml.kernel.org/r/ce2251ef49e1727a9a40531d1996660b05462bd2.1615279825.git.baolin.wang@linux.alibaba.comSigned-off-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Acked-by: Minchan Kim <minchan@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/cma.c

@@ -500,7 +500,7 @@ struct page *cma_alloc(struct cma *cma, size_t count, unsigned int align,
 	}
 
 	if (ret && !no_warn) {
-		pr_err("%s: %s: alloc failed, req-size: %zu pages, ret: %d\n",
+		pr_err_ratelimited("%s: %s: alloc failed, req-size: %zu pages, ret: %d\n",
 				   __func__, cma->name, count, ret);
 		cma_debug_show_areas(cma);
 	}