linux-kernel - Re: [PATCH v2 1/3] lib/vsprintf: Avoid redundant work with 0 size

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Date:   Sun, 30 Jan 2022 15:57:14 -0500
From:   Waiman Long <longman@...hat.com>
To:     David Rientjes <rientjes@...gle.com>
Cc:     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>,
        linux-kernel@...r.kernel.org, cgroups@...r.kernel.org,
        linux-mm@...ck.org, Ira Weiny <ira.weiny@...el.com>,
        Rafael Aquini <aquini@...hat.com>
Subject: Re: [PATCH v2 1/3] lib/vsprintf: Avoid redundant work with 0 size

On 1/30/22 15:49, David Rientjes wrote:
> On Sat, 29 Jan 2022, Waiman Long wrote:
>
>> 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.
>>
>> Signed-off-by: Waiman Long <longman@...hat.com>
>> ---
>>   lib/vsprintf.c | 8 +++++---
>>   1 file changed, 5 insertions(+), 3 deletions(-)
>>
>> diff --git a/lib/vsprintf.c b/lib/vsprintf.c
>> index 3b8129dd374c..a65df546fb06 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 (!size)
>> +		return 0;
> Nit: any reason this shouldn't be unlikely()?  If the conditional for
> i < size is likely(), this seems assumed already?

Good suggestion. Will make the change in the next version.

Cheers,
Longman