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

On Thu 29-12-16 18:26:38, Jaewon Kim wrote:

On 2016e?? 12i?? 29i? 1/4  18:14, Michal Hocko wrote:

quoted

On Thu 29-12-16 11:28:02, Jaewon Kim wrote:

quoted

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

Could you be more specific why this part is useful?

Hi
Without this patch we do not know why CMA allocation failed.

Yes, I understand the first part

Additionally in case of ENOMEM, with bitmap status we can figure out that

The code doesn't seem to check for ENOMEM though

if it is too small CMA region issue or if it is fragmentation issue.

then please describe that in the changelog. If I got it right the above
would tell us that the fragmentation is the problem, right?

quoted

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Signed-off-by: Jaewon Kim <redacted>
---
 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: ");

I guess you want pr_info (or maybe pr_debug) here

quoted

quoted

+		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);

pr_cont

quoted

quoted

+			nr_total += nr;
+			start = bitmap_no + nr;
+		}
+		printk("=>%u pages, total: %lu pages\n", nr_total, cma->count);

pr_cont

quoted

quoted

+		mutex_unlock(&cma->lock);
+	}
+
 	return page;
 }
 
-- 
1.9.1

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-- 
Michal Hocko
SUSE Labs

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