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SubjectRe: [PATCH 5/5] lockdep: pack subclass/trylock/read/check into a single argument
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)) ?

Suprizingly it helps a bit. Still "size vmlinux" is worse than with
bitmasks.

But I agreed that the code looks simpler with bitfields, so perhaps
this patch is better.

Oleg.



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