Re: [RFC 1/1] mm: Add per-task struct tlb counters

[Joe Damato <jdamato@fastly.com>]

On Wed, Sep 14, 2022 at 07:15:07AM -0700, Joe Damato wrote:
> On Wed, Sep 14, 2022 at 12:40:55AM -0700, Dave Hansen wrote:
> > On 9/13/22 18:51, Joe Damato wrote:
> > > TLB shootdowns are tracked globally, but on a busy system it can be
> > > difficult to disambiguate the source of TLB shootdowns.
> > > 
> > > Add two counter fields:
> > > 	- nrtlbflush: number of tlb flush events received
> > > 	- ngtlbflush: number of tlb flush events generated
> > > 
> > > Expose those fields in /proc/[pid]/stat so that they can be analyzed
> > > alongside similar metrics (e.g. min_flt and maj_flt).
> > 
> > On x86 at least, we already have two other ways to count flushes.  You
> > even quoted them with your patch:
> > 
> > >  	count_vm_tlb_event(NR_TLB_REMOTE_FLUSH);
> > > +	current->ngtlbflush++;
> > >  	if (info->end == TLB_FLUSH_ALL)
> > >  		trace_tlb_flush(TLB_REMOTE_SEND_IPI, TLB_FLUSH_ALL);
> > 
> > Granted, the count_vm_tlb...() one is debugging only.  But, did you try
> > to use those other mechanisms?  For instance, could you patch
> > count_vm_tlb_event()? 
> 
> I tried to address this in my cover letter[1]...

Err, I forgot the [1]:
https://lore.kernel.org/linux-mm/1663120270-2673-1-git-send-email-jdamato@fastly.com/