linux-kernel - [PATCH v3 1/4] lib/vsprintf: Avoid redundant work with 0 size

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Message-Id: <20220131192308.608837-2-longman@redhat.com>
Date:   Mon, 31 Jan 2022 14:23:05 -0500
From:   Waiman Long <longman@...hat.com>
To:     Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...nel.org>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Petr Mladek <pmladek@...e.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Sergey Senozhatsky <senozhatsky@...omium.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>
Cc:     linux-kernel@...r.kernel.org, cgroups@...r.kernel.org,
        linux-mm@...ck.org, Ira Weiny <ira.weiny@...el.com>,
        Mike Rapoport <rppt@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Roman Gushchin <guro@...com>,
        Rafael Aquini <aquini@...hat.com>,
        Waiman Long <longman@...hat.com>
Subject: [PATCH v3 1/4] lib/vsprintf: Avoid redundant work with 0 size

For *scnprintf(), vsnprintf() is always called even if the input size is
0. That is a waste of time, so just return 0 in this case.

Note that vsnprintf() will never return -1 to indicate an error. So
skipping the call to vsnprintf() when size is 0 will have no functional
impact at all.

Signed-off-by: Waiman Long <longman@...hat.com>
Acked-by: David Rientjes <rientjes@...gle.com>
Reviewed-by: Sergey Senozhatsky <senozhatsky@...omium.org>
Acked-by: Roman Gushchin <guro@...com>
---
 lib/vsprintf.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index 3b8129dd374c..d419154b47bb 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -2895,13 +2895,15 @@ int vscnprintf(char *buf, size_t size, const char *fmt, va_list args)
 {
 	int i;
 
+	if (unlikely(!size))
+		return 0;
+
 	i = vsnprintf(buf, size, fmt, args);
 
 	if (likely(i < size))
 		return i;
-	if (size != 0)
-		return size - 1;
-	return 0;
+
+	return size - 1;
 }
 EXPORT_SYMBOL(vscnprintf);
 
-- 
2.27.0