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

On 05/09/2018 04:31 PM, Dave Hansen wrote:
> On 05/07/2018 06:16 PM, prakash.sangappa wrote:
>> It will be /proc/<pid>/numa_vamaps. Yes, the behavior will be
>> different with respect to seeking. Output will still be text and
>> the format will be same.
>> I want to get feedback on this approach.
> I think it would be really great if you can write down a list of the
> things you actually want to accomplish. Dare I say: you need a
> requirements list.
> The numa_vamaps approach continues down the path of an ever-growing list
> of highly-specialized /proc/<pid> files. I don't think that is
> sustainable, even if it has been our trajectory for many years.
> Pagemap wasn't exactly a shining example of us getting new ABIs right,
> but it sounds like something along those is what we need.

Just sent out a V2 patch. This patch simplifies the file content. It
only provides VA range to numa node id information.

The requirement is basically observability for performance analysis.

- Need to be able to determine VA range to numa node id information.
Which also gives an idea of which range has memory allocated.

- The proc file /proc/<pid>/numa_vamaps is in text so it is easy to
directly view.

The V2 patch supports seeking to a particular process VA from where
the application could read the VA to numa node id information.

Also added the 'PTRACE_MODE_READ_REALCREDS' check when opening the
file /proc file as was indicated by Michal Hacko

The VA range to numa node information from this file can be used by pmap.

Here is a sample from a prototype change to pmap(procps) showing
numa node information, gathered from the new 'numa_vamaps' file.

$ ./rpmap -L -A 00000000006f8000,00007f5f730fe000 31423|more
31423: bash
00000000006f8000 16K N1 rw--- bash
00000000006fc000 4K N0 rw--- bash
00000000006fd000 4K N0 rw--- [ anon ]
00000000006fe000 8K N1 rw--- [ anon ]
0000000000700000 4K N0 rw--- [ anon ]
0000000000701000 4K N1 rw--- [ anon ]
0000000000702000 4K N0 rw--- [ anon ]
0000000000ce8000 52K N0 rw--- [ anon ]
0000000000cf5000 4K N1 rw--- [ anon ]
0000000000cf6000 28K N0 rw--- [ anon ]
0000000000cfd000 4K N1 rw--- [ anon ]
0000000000cfe000 28K N0 rw--- [ anon ]
0000000000d05000 504K N1 rw--- [ anon ]
0000000000d83000 8K N0 rw--- [ anon ]
0000000000d85000 932K N1 rw--- [ anon ]
0000000000e6e000 4K - rw--- [ anon ]
0000000000e6f000 168K N1 rw--- [ anon ]
00007f5f72ef4000 4K N2 r-x--
00007f5f72ef5000 40K N0 r-x--
00007f5f72eff000 2044K - -----
00007f5f730fe000 4K N0 r----
total 3868K


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