Messages in this thread |  | | Date | Wed, 22 Oct 2014 21:54:35 +0200 | From | Peter Zijlstra <> | Subject | Re: perf: Translating mmap2 ids into socket info? |
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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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