Re: [patch] mm, memcg: avoid unnecessary function call when memcgis disabled

[Kamezawa Hiroyuki]

(2012/11/21 6:49), Andrew Morton wrote:
> On Mon, 19 Nov 2012 17:44:34 -0800 (PST)
> David Rientjes <rientjes@xxxxxxxxxx> wrote:
>
> > While profiling numa/core v16 with cgroup_disable=memory on the command
> > line, I noticed mem_cgroup_count_vm_event() still showed up as high as
> > 0.60% in perftop.
> >
> > This occurs because the function is called extremely often even when memcg
> > is disabled.
> >
> > To fix this, inline the check for mem_cgroup_disabled() so we avoid the
> > unnecessary function call if memcg is disabled.
> >
> > ...
> >
> > diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> > --- a/include/linux/memcontrol.h
> > +++ b/include/linux/memcontrol.h
> > @@ -181,7 +181,14 @@ unsigned long mem_cgroup_soft_limit_reclaim(struct zone *zone, int order,
> >   						gfp_t gfp_mask,
> >   						unsigned long *total_scanned);
> >
> > -void mem_cgroup_count_vm_event(struct mm_struct *mm, enum vm_event_item idx);
> > +void __mem_cgroup_count_vm_event(struct mm_struct *mm, enum vm_event_item idx);
> > +static inline void mem_cgroup_count_vm_event(struct mm_struct *mm,
> > +					     enum vm_event_item idx)
> > +{
> > +	if (mem_cgroup_disabled() || !mm)
> > +		return;
> > +	__mem_cgroup_count_vm_event(mm, idx);
> > +}
>
> Does the !mm case occur frequently enough to justify inlining it, or
> should that test remain out-of-line?
I think this should be out-of-line.

Thanks,
-Kame

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