Re: [RFC PATCH] Add /proc/<pid>/numa_vamaps for numa node information

[Prakash Sangappa]

On 5/4/18 7:57 AM, Christopher Lameter wrote:
> On Thu, 3 May 2018, prakash.sangappa wrote:
>
> > > > exact numa node from where the pages have been allocated.
> > > Cant you write a small script that scans the information in numa_maps and
> > > then displays the total pages per NUMA node and then a list of which
> > > ranges have how many pages on a particular node?
> > Don't think we can determine which numa node a given user process
> > address range has pages from, based on the existing 'numa_maps' file.
> Well the information is contained in numa_maps I thought. What is missing?

Currently 'numa_maps' gives a list of numa nodes, memory is allocated per
VMA.
Ex. we get something like from numa_maps.

04000Â N0=1,N2=2 kernelpagesize_KB=4

First is the start address of a VMA. This VMA could be much larger then 
3 4k pages.
It does not say which address in the VMA has the pages mapped.

> > > > reading this file will not be restricted(i.e requiring CAP_SYS_ADMIN).
> > > So a prime motivator here is security restricted access to numa_maps?
> > No it is the opposite. A regular user should be able to determine
> > numa node information.
> That used to be the case until changes were made to the permissions for
> reading numa_maps.