[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.
But we did not know error reason so far. This patch prints the error value.

Additionally if CONFIG_CMA_DEBUG is enabled, this patch shows bitmap status to
know available pages. Actually CMA internally try all available regions because
some regions can be failed because of EBUSY. Bitmap status is useful to know in
detail on both ENONEM and EBUSY;
 ENOMEM: not tried at all because of no available region
         it could be too small total region or could be fragmentation issue
 EBUSY:  tried some region but all failed

This is an ENOMEM example with this patch.
[   13.250961]  [1:   Binder:715_1:  846] cma: cma_alloc: alloc failed, req-size: 256 pages, ret: -12
Avabile pages also will be shown if CONFIG_CMA_DEBUG is enabled
[   13.251052]  [1:   Binder:715_1:  846] cma: number of available pages: 4@572+7@585+7@601+8@632+38@730+166@1114+127@1921=>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..1bcd9db 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)
+        pr_info("%s: alloc failed, req-size: %zu pages, ret: %d\n",
+            __func__, count, ret);
+#ifdef CONFIG_CMA_DEBUG
+    if (ret != 0) {
+        unsigned int nr, nr_total = 0;
+        unsigned long next_set_bit;
+
+        mutex_lock(&cma->lock);
+        pr_info("number of available pages: ");
+        start = 0;
+        for (;;) {
+            bitmap_no = find_next_zero_bit(cma->bitmap, cma->count, start);
+            if (bitmap_no >= cma->count)
+                break;
+            next_set_bit = find_next_bit(cma->bitmap, cma->count, bitmap_no);
+            nr = next_set_bit - bitmap_no;
+            pr_cont("%s%u@%lu", nr_total ? "+" : "", nr, bitmap_no);
+            nr_total += nr;
+            start = bitmap_no + nr;
+        }
+        pr_cont("=>%u pages, total: %lu pages\n", nr_total, cma->count);
+        mutex_unlock(&cma->lock);
+    }
+#endif
+
     return page;
 }
 
-- 
1.9.1