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

["prakash.sangappa" <prakash.sangappa@oracle.com>]

On 05/02/2018 02:33 PM, Andrew Morton wrote:
> On Tue,  1 May 2018 22:58:06 -0700 Prakash Sangappa <prakash.sangappa@oracle.com> 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.

>> There have been couple of previous patch proposals to provide numa node
>> information based on pfn or physical address. They seem to have not made
>> progress. Also it would appear reading numa node information based on PFN
>> or physical address will require privileges(CAP_SYS_ADMIN) similar to
>> reading PFN info from /proc/<pid>/pagemap.
>>
>> See
>> https://marc.info/?t=139630938200001&r=1&w=2
>>
>> https://marc.info/?t=139718724400001&r=1&w=2
> OK, let's hope that these people will be able to provide their review,
> feedback, testing, etc.  You missed a couple (Dave, Naoya).
>
>>   fs/proc/base.c     |   2 +
>>   fs/proc/internal.h |   3 +
>>   fs/proc/task_mmu.c | 299 ++++++++++++++++++++++++++++++++++++++++++++++++++++-
> Some Documentation/ updates seem appropriate.  I suggest you grep the
> directory for "numa_maps" to find suitable locations.

Sure, I can update Documentation/filesystems/proc.txt file which is
where 'numa_maps' is documented.

>
> And a quick build check shows that `size fs/proc/task_mmu.o' gets quite
> a bit larger when CONFIG_SMP=n and CONFIG_NUMA=n.  That seems wrong -
> please see if you can eliminate the bloat from systems which don't need
> this feature.
>
>
Ok will take a look.