linux-kernel - [PATCH] mm/damon/dbgfs: Optimize target

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Message-Id: <20211021085611.81211-1-xhao@linux.alibaba.com>
Date:   Thu, 21 Oct 2021 16:56:11 +0800
From:   Xin Hao <xhao@...ux.alibaba.com>
To:     sjpark@...zon.de
Cc:     xhao@...ux.alibaba.com, akpm@...ux-foundation.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: [PATCH] mm/damon/dbgfs: Optimize target_ids interface write operation

When writing some pids to target_ids interface, calling scanf()
to get 'id' may be failed. If the value of '*nr_ids' is 0 at this time,
there is no need to return 'ids' here, we just need to release it and
return NULL pointer to improve related code operation efficiency.

Signed-off-by: Xin Hao <xhao@...ux.alibaba.com>
---
 mm/damon/dbgfs.c | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/mm/damon/dbgfs.c b/mm/damon/dbgfs.c
index a02cf6bee8e8..2d77bf579ffb 100644
--- a/mm/damon/dbgfs.c
+++ b/mm/damon/dbgfs.c
@@ -308,21 +308,25 @@ static unsigned long *str_to_target_ids(const char *str, ssize_t len,
 	unsigned long *ids;
 	const int max_nr_ids = 32;
 	unsigned long id;
-	int pos = 0, parsed, ret;
+	int pos = 0, parsed;
 
 	*nr_ids = 0;
 	ids = kmalloc_array(max_nr_ids, sizeof(id), GFP_KERNEL);
 	if (!ids)
 		return NULL;
 	while (*nr_ids < max_nr_ids && pos < len) {
-		ret = sscanf(&str[pos], "%lu%n", &id, &parsed);
-		pos += parsed;
-		if (ret != 1)
+		if (sscanf(&str[pos], "%lu%n", &id, &parsed) != 1)
 			break;
+		pos += parsed;
 		ids[*nr_ids] = id;
 		*nr_ids += 1;
 	}
 
+	if (!*nr_ids) {
+		kfree(ids);
+		return NULL;
+	}
+
 	return ids;
 }
 
-- 
2.31.0