Re: [PATCH] Makefiles: Disable unused-variable warning (was: Re:[PATCH 1/6] memcg: fix unused variable warning)

[Michal Hocko]

On Thu 29-12-11 13:08:50, Kirill A. Shutemov wrote:
> On Thu, Dec 29, 2011 at 11:42:30AM +0100, Michal Hocko wrote:
> > On Tue 27-12-11 20:26:13, Kirill A. Shutemov wrote:
> > > On Tue, Dec 27, 2011 at 02:57:52PM +0100, Michal Hocko wrote:
> > > > On Sat 24-12-11 05:00:14, Kirill A. Shutemov wrote:
> > > > > From: "Kirill A. Shutemov" <kirill@xxxxxxxxxxxxx>
> > > > > 
> > > > > mm/memcontrol.c: In function âmemcg_check_eventsâ:
> > > > > mm/memcontrol.c:784:22: warning: unused variable âdo_numainfoâ [-Wunused-variable]
> > > > > 
> > > > > Signed-off-by: Kirill A. Shutemov <kirill@xxxxxxxxxxxxx>
> > > > > ---
> > > > >  mm/memcontrol.c |    7 ++++---
> > > > >  1 files changed, 4 insertions(+), 3 deletions(-)
> > > > > 
> > > > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> > > > > index d643bd6..a5e92bd 100644
> > > > > --- a/mm/memcontrol.c
> > > > > +++ b/mm/memcontrol.c
> > > > > @@ -781,14 +781,15 @@ static void memcg_check_events(struct mem_cgroup *memcg, struct page *page)
> > > > >  	/* threshold event is triggered in finer grain than soft limit */
> > > > >  	if (unlikely(mem_cgroup_event_ratelimit(memcg,
> > > > >  						MEM_CGROUP_TARGET_THRESH))) {
> > > > > -		bool do_softlimit, do_numainfo;
> > > > > +		bool do_softlimit;
> > > > >  
> > > > > -		do_softlimit = mem_cgroup_event_ratelimit(memcg,
> > > > > -						MEM_CGROUP_TARGET_SOFTLIMIT);
> > > > >  #if MAX_NUMNODES > 1
> > > > > +		bool do_numainfo;
> > > > >  		do_numainfo = mem_cgroup_event_ratelimit(memcg,
> > > > >  						MEM_CGROUP_TARGET_NUMAINFO);
> > > > >  #endif
> > > > > +		do_softlimit = mem_cgroup_event_ratelimit(memcg,
> > > > > +						MEM_CGROUP_TARGET_SOFTLIMIT);
> > > > 
> > > > I don't like this very much. Maybe we should get rid of both do_* and
> > > > do it with flags? But maybe it is not worth the additional code at
> > > > all...
> > > 
> > > Something like this (untested):
> > > ====
> > > From f57e1a2e1aaaa167c75b963d5bf12fcbdd3331b8 Mon Sep 17 00:00:00 2001
> > > From: "Kirill A. Shutemov" <kirill@xxxxxxxxxxxxx>
> > > Date: Tue, 27 Dec 2011 20:17:13 +0200
> > > Subject: [PATCH] memcg: cleanup memcg_check_events()
> > > 
> > > Signed-off-by: Kirill A. Shutemov <kirill@xxxxxxxxxxxxx>
> > 
> > The patch looks correct but I am still not sure this is worth fixing in
> > the code rather than disabling Wunused-variable.
> 
> Does it look better then original code from your POV?
> 
> It's a bit cleaner, I think.

Yes it is less hakish than the previous one which relied on having
#ifdef block before any other code in the block.

> 
> > 
> > > ---
> > >  mm/memcontrol.c |   42 ++++++++++++++++++++++++------------------
> > >  1 files changed, 24 insertions(+), 18 deletions(-)
> > > 
> > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> > > index d643bd6..40c2236 100644
> > > --- a/mm/memcontrol.c
> > > +++ b/mm/memcontrol.c
> > > @@ -108,11 +108,12 @@ enum mem_cgroup_events_index {
> > >   * than using jiffies etc. to handle periodic memcg event.
> > >   */
> > >  enum mem_cgroup_events_target {
> > > -	MEM_CGROUP_TARGET_THRESH,
> > > -	MEM_CGROUP_TARGET_SOFTLIMIT,
> > > -	MEM_CGROUP_TARGET_NUMAINFO,
> > > -	MEM_CGROUP_NTARGETS,
> > > +	MEM_CGROUP_TARGET_THRESH	= BIT(1),
> > > +	MEM_CGROUP_TARGET_SOFTLIMIT	= BIT(2),
> > > +	MEM_CGROUP_TARGET_NUMAINFO	= BIT(3),
> > >  };
> > > +#define MEM_CGROUP_NTARGETS 3
> > > +
> > >  #define THRESHOLDS_EVENTS_TARGET (128)
> > >  #define SOFTLIMIT_EVENTS_TARGET (1024)
> > >  #define NUMAINFO_EVENTS_TARGET	(1024)
> > > @@ -743,7 +744,7 @@ static unsigned long mem_cgroup_nr_lru_pages(struct mem_cgroup *memcg,
> > >  	return total;
> > >  }
> > >  
> > > -static bool mem_cgroup_event_ratelimit(struct mem_cgroup *memcg,
> > > +static int mem_cgroup_event_ratelimit(struct mem_cgroup *memcg,
> > >  				       enum mem_cgroup_events_target target)
> > >  {
> > >  	unsigned long val, next;
> > > @@ -766,9 +767,9 @@ static bool mem_cgroup_event_ratelimit(struct mem_cgroup *memcg,
> > >  			break;
> > >  		}
> > >  		__this_cpu_write(memcg->stat->targets[target], next);
> > > -		return true;
> > > +		return target;
> > >  	}
> > > -	return false;
> > > +	return 0;
> > >  }
> > >  
> > >  /*
> > > @@ -777,29 +778,34 @@ static bool mem_cgroup_event_ratelimit(struct mem_cgroup *memcg,
> > >   */
> > >  static void memcg_check_events(struct mem_cgroup *memcg, struct page *page)
> > >  {
> > > +	int flags;
> > > +
> > >  	preempt_disable();
> > > -	/* threshold event is triggered in finer grain than soft limit */
> > > -	if (unlikely(mem_cgroup_event_ratelimit(memcg,
> > > -						MEM_CGROUP_TARGET_THRESH))) {
> > > -		bool do_softlimit, do_numainfo;
> > > +	flags = mem_cgroup_event_ratelimit(memcg, MEM_CGROUP_TARGET_THRESH);
> > >  
> > > -		do_softlimit = mem_cgroup_event_ratelimit(memcg,
> > > +	/*
> > > +	 * Threshold event is triggered in finer grain than soft limit
> > > +	 * and numainfo
> > > +	 */
> > > +	if (unlikely(flags)) {
> > > +		flags |= mem_cgroup_event_ratelimit(memcg,
> > >  						MEM_CGROUP_TARGET_SOFTLIMIT);
> > >  #if MAX_NUMNODES > 1
> > > -		do_numainfo = mem_cgroup_event_ratelimit(memcg,
> > > +		flags |= mem_cgroup_event_ratelimit(memcg,
> > >  						MEM_CGROUP_TARGET_NUMAINFO);
> > >  #endif
> > > -		preempt_enable();
> > > +	}
> > > +	preempt_enable();
> > >  
> > > +	if (unlikely(flags)) {
> > >  		mem_cgroup_threshold(memcg);
> > > -		if (unlikely(do_softlimit))
> > > +		if (unlikely(flags & MEM_CGROUP_TARGET_SOFTLIMIT))
> > >  			mem_cgroup_update_tree(memcg, page);
> > >  #if MAX_NUMNODES > 1
> > > -		if (unlikely(do_numainfo))
> > > +		if (unlikely(flags & MEM_CGROUP_TARGET_NUMAINFO))
> > >  			atomic_inc(&memcg->numainfo_events);
> > >  #endif
> > > -	} else
> > > -		preempt_enable();
> > > +	}
> > >  }
> > >  
> > >  struct mem_cgroup *mem_cgroup_from_cont(struct cgroup *cont)
> > > -- 
> > > 1.7.7.3
> > 
> > -- 
> > Michal Hocko
> > SUSE Labs
> > SUSE LINUX s.r.o.
> > Lihovarska 1060/12
> > 190 00 Praha 9    
> > Czech Republic
> 
> -- 
>  Kirill A. Shutemov
> --
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-- 
Michal Hocko
SUSE Labs
SUSE LINUX s.r.o.
Lihovarska 1060/12
190 00 Praha 9    
Czech Republic
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