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

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Date:   Wed, 14 Sep 2022 07:25:24 -0700
From:   Joe Damato <jdamato@...tly.com>
To:     Dave Hansen <dave.hansen@...el.com>
Cc:     x86@...nel.org, linux-mm@...ck.org,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Valentin Schneider <vschneid@...hat.com>,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [RFC 1/1] mm: Add per-task struct tlb counters

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/