On Wed, 21 Nov 2012, Michal Hocko wrote: > 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. Here's a guess: as Ying's 456f998e patch started out in akpm's tree, shmem.c was calling mem_cgroup_count_vm_event(current->mm, PGMAJFAULT). Then I insisted that was inconsistent with how we usually account when one task touches another's address space, and rearranged it to work on vma->vm_mm instead. Done the original way, if the touching task were a kernel daemon (KSM's ksmd comes to my mind), then the current->mm could well have been NULL. I agree with you that it looks redundant now. Hugh -- 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>