Date: Wed, 22 Oct 2014 21:54:35 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Don Zickus <dzickus@redhat.com>, LKML <linux-kernel@vger.kernel.org>,
        eranian@google.com, Andi Kleen <andi@firstfloor.org>, jolsa@redhat.com,
        jmario@redhat.com, rfowles@redhat.com
Subject: Re: perf:  Translating mmap2 ids into socket info?
Message-ID: <20141022195435.GK21513@worktop.programming.kicks-ass.net>
References: <20141022162026.GG135937@redhat.com>
 <20141022164510.GJ21513@worktop.programming.kicks-ass.net>
 <20141022174226.GF4160@kernel.org>
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On Wed, Oct 22, 2014 at 02:42:26PM -0300, Arnaldo Carvalho de Melo wrote:
> Em Wed, Oct 22, 2014 at 06:45:10PM +0200, Peter Zijlstra escreveu:
> > On Wed, Oct 22, 2014 at 12:20:26PM -0400, Don Zickus wrote:
> > > Our cache-to-cache tool noticed the slowdown but we couldn't understand
> > > why because we had falsely assumed the memory was allocated on the local
> > > node but instead it was on the remote node.
>  
> > But in general, you can never say for user memory, since that has the
> > process page table mapping in between, the user virtual address is
> > unrelated to backing (and can change frequently and without
> > notification).
>  
> > Therefore the mmap(2) information is useless for this, it only concerns
> > user memory.
> 
> So what you are saying is that it is difficult to have some sort of
> mechanism that an mmap moved from one node to another, when that
> happens, i.e. a new tracepoint for that?

Node is per page, not per mapping. Every single page in a mmap can have
a different node (assuming enough nodes etc..), and it can change at
relatively high frequency.
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