Re: perf: Translating mmap2 ids into socket info?

[Peter Zijlstra <peterz@infradead.org>]

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.