On Tue 20-11-12 13:49:32, 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?
Now that you've asked about it I started looking around and I cannot see
how mm can ever be NULL. The condition is there since the very beginning
(456f998e memcg: add the pagefault count into memcg stats) but all the
callers are page fault handlers and those shouldn't have mm==NULL.
Or is there anything obvious I am missing?
Ying, the whole thread starts https://lkml.org/lkml/2012/11/19/545 but
the primary question is why we need !mm test for mem_cgroup_count_vm_event
at all.
Thanks!
--
Michal Hocko
SUSE Labs
--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@xxxxxxxxx. For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>