linux-kernel - Re: [RFC PATCH] Add /proc/<pid>/numa

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Message-ID: <20180510074254.GE32366@dhcp22.suse.cz>
Date:   Thu, 10 May 2018 09:42:54 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Prakash Sangappa <prakash.sangappa@...cle.com>
Cc:     Christopher Lameter <cl@...ux.com>, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, linux-api@...r.kernel.org,
        akpm@...ux-foundation.org, kirill.shutemov@...ux.intel.com,
        n-horiguchi@...jp.nec.com, drepper@...il.com, rientjes@...gle.com
Subject: Re: [RFC PATCH] Add /proc/<pid>/numa_vamaps for numa node information

On Fri 04-05-18 09:18:11, Prakash Sangappa wrote:
> 
> 
> On 5/4/18 4:12 AM, Michal Hocko wrote:
> > On Thu 03-05-18 15:39:49, prakash.sangappa wrote:
> > > 
> > > On 05/03/2018 11:03 AM, Christopher Lameter wrote:
> > > > On Tue, 1 May 2018, Prakash Sangappa wrote:
> > > > 
> > > > > For analysis purpose it is useful to have numa node information
> > > > > corresponding mapped address ranges of the process. Currently
> > > > > /proc/<pid>/numa_maps provides list of numa nodes from where pages are
> > > > > allocated per VMA of the process. This is not useful if an user needs to
> > > > > determine which numa node the mapped pages are allocated from for a
> > > > > particular address range. It would have helped if the numa node information
> > > > > presented in /proc/<pid>/numa_maps was broken down by VA ranges showing the
> > > > > 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.
> > yes we have. See move_pages...
> 
> Sure using move_pages, not based on just 'numa_maps'.
> 
> > > > > 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.
> > Well, that breaks the layout randomization, doesn't it?
> 
> Exposing numa node information itself should not break randomization right?

I thought you planned to expose address ranges for each numa node as
well. /me confused.

> It would be upto the application. In case of randomization, the application
> could generate  address range traces of interest for debugging and then
> using numa node information one could determine where the memory is laid
> out for analysis.

... even more confused

-- 
Michal Hocko
SUSE Labs