Re: perf: Translating mmap2 ids into socket info?

[Arnaldo Carvalho de Melo <acme@kernel.org>]

Em Wed, Oct 22, 2014 at 02:42:26PM -0300, Arnaldo Carvalho de Melo escreveu:
> 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?

Humm, so, after reading a bit more, I see that we can figure out which
ranges are in which NUMA nodes (like shown in dmesg), and we have the
phys addr, so is this just a matter of perf tooling complement the
information the kernel provides on mmap2 (and the hardware provides on
those events)?

- Arnaldo