[PATCH] mm: cma: print allocation failure reason and bitmap status

[Jaewon Kim]

There are many reasons of CMA allocation failure such as EBUSY, ENOMEM, EINTR.
This patch prints the error value and bitmap status to know available pages
regarding fragmentation.

This is an ENOMEM example with this patch.
[   11.616321]  [2:   Binder:711_1:  740] cma: cma_alloc: alloc failed, req-size: 256 pages, ret: -12
[   11.616365]  [2:   Binder:711_1:  740] number of available pages: 4+7+7+8+38+166+127=>357 pages, total: 2048 pages

Signed-off-by: Jaewon Kim <jaewon31.kim@xxxxxxxxxxx>
---
 mm/cma.c | 29 ++++++++++++++++++++++++++++-
 1 file changed, 28 insertions(+), 1 deletion(-)

diff --git a/mm/cma.c b/mm/cma.c
index c960459..535aa39 100644
--- a/mm/cma.c
+++ b/mm/cma.c
@@ -369,7 +369,7 @@ struct page *cma_alloc(struct cma *cma, size_t count, unsigned int align)
 	unsigned long start = 0;
 	unsigned long bitmap_maxno, bitmap_no, bitmap_count;
 	struct page *page = NULL;
-	int ret;
+	int ret = -ENOMEM;
 
 	if (!cma || !cma->count)
 		return NULL;
@@ -427,6 +427,33 @@ struct page *cma_alloc(struct cma *cma, size_t count, unsigned int align)
 	trace_cma_alloc(pfn, page, count, align);
 
 	pr_debug("%s(): returned %p\n", __func__, page);
+
+	if (ret != 0) {
+		unsigned int nr, nr_total = 0;
+		unsigned long next_set_bit;
+
+		pr_info("%s: alloc failed, req-size: %zu pages, ret: %d\n",
+			__func__, count, ret);
+		mutex_lock(&cma->lock);
+		printk("number of available pages: ");
+		start = 0;
+		for (;;) {
+			bitmap_no = find_next_zero_bit(cma->bitmap, cma->count, start);
+			next_set_bit = find_next_bit(cma->bitmap, cma->count, bitmap_no);
+			nr = next_set_bit - bitmap_no;
+			if (bitmap_no >= cma->count)
+				break;
+			if (nr_total == 0)
+				printk("%u", nr);
+			else
+				printk("+%u", nr);
+			nr_total += nr;
+			start = bitmap_no + nr;
+		}
+		printk("=>%u pages, total: %lu pages\n", nr_total, cma->count);
+		mutex_unlock(&cma->lock);
+	}
+
 	return page;
 }
 
-- 
1.9.1