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Message-ID: <53f74ef1-e097-ea2a-84ef-2d34367e60eb@redhat.com>
Date:   Sun, 30 Jan 2022 15:57:14 -0500
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Subject: Re: [PATCH v2 1/3] lib/vsprintf: Avoid redundant work with 0 size
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To:     David Rientjes <rientjes@google.com>
Cc:     Johannes Weiner <hannes@cmpxchg.org>,
        Michal Hocko <mhocko@kernel.org>,
        Vladimir Davydov <vdavydov.dev@gmail.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Petr Mladek <pmladek@suse.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Sergey Senozhatsky <senozhatsky@chromium.org>,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        Rasmus Villemoes <linux@rasmusvillemoes.dk>,
        linux-kernel@vger.kernel.org, cgroups@vger.kernel.org,
        linux-mm@kvack.org, Ira Weiny <ira.weiny@intel.com>,
        Rafael Aquini <aquini@redhat.com>
References: <20220129205315.478628-1-longman@redhat.com>
 <20220129205315.478628-2-longman@redhat.com>
 <d99b3c4b-7b6e-529-6e4b-b91b65c92d81@google.com>
From:   Waiman Long <longman@redhat.com>
In-Reply-To: <d99b3c4b-7b6e-529-6e4b-b91b65c92d81@google.com>
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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@redhat.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