linux-kernel - Re: [PATCH] proc: much faster /proc/vmstat

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Sun, 7 Aug 2016 02:35:13 +0100
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Alexey Dobriyan <adobriyan@...il.com>
Cc:	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] proc: much faster /proc/vmstat

On Sat, Aug 06, 2016 at 03:54:56PM +0300, Alexey Dobriyan wrote:

[sprintf sucks, let's convert numbers manually]

> --- a/mm/vmstat.c
> +++ b/mm/vmstat.c
> @@ -1592,7 +1592,10 @@ static int vmstat_show(struct seq_file *m, void *arg)
>  {
>  	unsigned long *l = arg;
>  	unsigned long off = l - (unsigned long *)m->private;
> -	seq_printf(m, "%s %lu\n", vmstat_text[off], *l);
> +
> +	seq_puts(m, vmstat_text[off]);
> +	seq_put_decimal_ull(m, ' ', *l);
> +	seq_putc(m, '\n');
>  	return 0;
>  }

If that manages to be a hotspot, we really should
	* educate the wankers responsible for the userland code in question,
until they repent and cease committing such abominations.
	* look into fixing vsnprintf().  

Seriously, what the hell is vsnprintf() doing that takes so much time?  It's
not as if it was a complex format anyway.  WTF is going on there?  Where is
it spending that much time?