linux-kernel - Re: [PATCH 5/5] lockdep: pack subclass/trylock/read/check into a single argument

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Message-ID: <20140121135306.7c01892c@gandalf.local.home>
Date:	Tue, 21 Jan 2014 13:53:06 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Dave Jones <davej@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Alan Stern <stern@...land.harvard.edu>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Ingo Molnar <mingo@...nel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Paul McKenney <paulmck@...ux.vnet.ibm.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 5/5] lockdep: pack subclass/trylock/read/check into a
 single argument

On Tue, 21 Jan 2014 19:43:10 +0100
Oleg Nesterov <oleg@...hat.com> wrote:

> On 01/21, Dave Jones wrote:
> >
> > On Tue, Jan 21, 2014 at 03:10:22PM +0100, Peter Zijlstra wrote:
> >  >
> >  > I tried the below but filed to see my vmlinux shrink, maybe I'm just not
> >  > building the right kernel, or otherwise GCC is stupid.
> >  >
> >  > -extern void lock_acquire(struct lockdep_map *lock, unsigned int subclass,
> >  > -			 int trylock, int read, int check,
> >  > -			 struct lockdep_map *nest_lock, unsigned long ip);
> >  > +struct lockdep_acquire_flags {
> >  > +	unsigned long subclass : 3;
> >  > +	unsigned long trylock  : 1;
> >  > +	unsigned long read     : 2;
> >  > +	unsigned long check    : 1;
> >  > +};
> >
> > As it's only 7 bits here, could we pack them into a char ?
> 
> Do you mean __attribute__((packed)) ?
> 

I think Dave means:

	unsigned char subclass	: 3;
	unsigned char trylock	: 1;
	unsigned char read	: 2;
	unsigned char check	: 1;

-- Steve
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