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

[Michal Hocko]

On Wed 02-05-18 16:43:58, prakash.sangappa wrote:
> 
> 
> On 05/02/2018 02:33 PM, Andrew Morton wrote:
> > On Tue,  1 May 2018 22:58:06 -0700 Prakash Sangappa <prakash.sangappa@xxxxxxxxxx> 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.
> > > 
> > > The format of /proc/<pid>/numa_maps file content is dependent on
> > > /proc/<pid>/maps file content as mentioned in the manpage. i.e one line
> > > entry for every VMA corresponding to entries in /proc/<pids>/maps file.
> > > Therefore changing the output of /proc/<pid>/numa_maps may not be possible.
> > > 
> > > Hence, this patch proposes adding file /proc/<pid>/numa_vamaps which will
> > > provide proper break down of VA ranges by numa node id from where the mapped
> > > pages are allocated. For Address ranges not having any pages mapped, a '-'
> > > is printed instead of numa node id. In addition, this file will include most
> > > of the other information currently presented in /proc/<pid>/numa_maps. The
> > > additional information included is for convenience. If this is not
> > > preferred, the patch could be modified to just provide VA range to numa node
> > > information as the rest of the information is already available thru
> > > /proc/<pid>/numa_maps file.
> > > 
> > > Since the VA range to numa node information does not include page's PFN,
> > > reading this file will not be restricted(i.e requiring CAP_SYS_ADMIN).
> > > 
> > > Here is the snippet from the new file content showing the format.
> > > 
> > > 00400000-00401000 N0=1 kernelpagesize_kB=4 mapped=1 file=/tmp/hmap2
> > > 00600000-00601000 N0=1 kernelpagesize_kB=4 anon=1 dirty=1 file=/tmp/hmap2
> > > 00601000-00602000 N0=1 kernelpagesize_kB=4 anon=1 dirty=1 file=/tmp/hmap2
> > > 7f0215600000-7f0215800000 N0=1 kernelpagesize_kB=2048 dirty=1 file=/mnt/f1
> > > 7f0215800000-7f0215c00000 -  file=/mnt/f1
> > > 7f0215c00000-7f0215e00000 N0=1 kernelpagesize_kB=2048 dirty=1 file=/mnt/f1
> > > 7f0215e00000-7f0216200000 -  file=/mnt/f1
> > > ..
> > > 7f0217ecb000-7f0217f20000 N0=85 kernelpagesize_kB=4 mapped=85 mapmax=51
> > >     file=/usr/lib64/libc-2.17.so
> > > 7f0217f20000-7f0217f30000 -  file=/usr/lib64/libc-2.17.so
> > > 7f0217f30000-7f0217f90000 N0=96 kernelpagesize_kB=4 mapped=96 mapmax=51
> > >     file=/usr/lib64/libc-2.17.so
> > > 7f0217f90000-7f0217fb0000 -  file=/usr/lib64/libc-2.17.so
> > > ..
> > > 
> > > The 'pmap' command can be enhanced to include an option to show numa node
> > > information which it can read from this new proc file. This will be a
> > > follow on proposal.
> > I'd like to hear rather more about the use-cases for this new
> > interface.  Why do people need it, what is the end-user benefit, etc?
> 
> This is mainly for debugging / performance analysis. Oracle Database
> team is looking to use this information.

But we do have an interface to query (e.g. move_pages) that your
application can use. I am really worried that the broken out per node
data can be really large (just take a large vma with interleaved policy
as an example). So is this really worth adding as a general purpose proc
interface?
-- 
Michal Hocko
SUSE Labs