linux-kernel - Re: [PATCH v10 1/4] cgroups: use bitmask to filter for_each

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Message-ID: <20150422154212.GE3007@worktop.Skamania.guest>
Date:	Wed, 22 Apr 2015 17:42:12 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Tejun Heo <tj@...nel.org>
Cc:	Aleksa Sarai <cyphar@...har.com>, lizefan@...wei.com,
	mingo@...hat.com, richard@....at, fweisbec@...il.com,
	linux-kernel@...r.kernel.org, cgroups@...r.kernel.org
Subject: Re: [PATCH v10 1/4] cgroups: use bitmask to filter for_each_subsys

On Wed, Apr 22, 2015 at 11:25:51AM -0400, Tejun Heo wrote:
> Hello, Aleksa.
> 
> On Sun, Apr 19, 2015 at 10:22:31PM +1000, Aleksa Sarai wrote:
> > -static int need_forkexit_callback __read_mostly;
> > +static int need_fork_callback __read_mostly;
> > +static int need_exit_callback __read_mostly;
> 
> These are bitmasks now, right?  Let's make them unsigned int.

If, as per the below you want to use the bitmap ops; it needs be
unsigned long.

> >  static struct cftype cgroup_dfl_base_files[];
> > +#define for_each_subsys_which(ss_mask, ss, ssid) \
> > +	for_each_subsys((ss), (ssid)) \
> > +		if ((ss_mask) & (1 << (ssid)))
> 
> Maybe using for_each_set_bit() is better?
> 
> #define for_each_subsys_which(ss_mask, ss, ssid)		\
> 	for_each_set_bit(ssid, &(ss_mask), CGROUP_SUBSYS_COUNT)	\
> 		if ((ss) = group_subsys[ssid] && false)		\
> 			;					\
> 		else

Clever that ;-)
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