tools/mm: Add thpmaps script to dump THP usage info

With the proliferation of large folios for file-backed memory, and more
recently the introduction of multi-size THP for anonymous memory, it is
becoming useful to be able to see exactly how large folios are mapped
into processes. For some architectures (e.g. arm64), if most memory is
mapped using contpte-sized and -aligned blocks, TLB usage can be
optimized so it's useful to see where these requirements are and are not
being met.

thpmaps is a Python utility that reads /proc/<pid>/smaps,
/proc/<pid>/pagemap and /proc/kpageflags to print information about how
transparent huge pages (both file and anon) are mapped to a specified
process or cgroup. It aims to help users debug and optimize their
workloads. In future we may wish to introduce stats directly into the
kernel (e.g. smaps or similar), but for now this provides a short term
solution without the need to introduce any new ABI.

Run with help option for a full listing of the arguments:

    # thpmaps --help

--8<--
usage: thpmaps [-h] [--pid pid] [--cgroup path] [--summary]
               [--cont size[KMG]] [--inc-smaps] [--inc-empty]
               [--periodic sleep_ms]

Prints information about how transparent huge pages are mapped to a
specified process or cgroup. Shows statistics for fully-mapped THPs of
every size, mapped both naturally aligned and unaligned for both file
and anonymous memory. See [anon|file]-thp-[aligned|unaligned]-<size>kB
keys. Shows statistics for mapped pages that belong to a THP but which
are not fully mapped. See [anon|file]-thp-partial keys. Optionally
shows statistics for naturally aligned, contiguous blocks of memory of
a specified size (when --cont is provided). See [anon|file]-cont-
aligned-<size>kB keys. Statistics are shown in kB and as a percentage
of either total anon or file memory as appropriate.

options:
  -h, --help           show this help message and exit
  --pid pid            Process id of the target process. Exactly one of
                       --pid and --cgroup must be provided.
  --cgroup path        Path to the target cgroup in sysfs. Iterates
                       over every pid in the cgroup. Exactly one of
                       --pid and --cgroup must be provided.
  --summary            Sum the per-vma statistics to provide a summary
                       over the whole process or cgroup.
  --cont size[KMG]     Adds anon and file stats for naturally aligned,
                       contiguously mapped blocks of the specified
                       size. May be issued multiple times to track
                       multiple sized blocks. Useful to infer e.g.
                       arm64 contpte and hpa mappings. Size must be a
                       power-of-2 number of pages.
  --inc-smaps          Include all numerical, additive
                       /proc/<pid>/smaps stats in the output.
  --inc-empty          Show all statistics including those whose value
                       is 0.
  --periodic sleep_ms  Run in a loop, polling every sleep_ms
                       milliseconds.

Requires root privilege to access pagemap and kpageflags.
--8<--

Example command to summarise fully and partially mapped THPs and 64K
contiguous blocks over all VMAs in a single process (--inc-empty forces
printing stats that are 0):

    # ./thpmaps --pid 10837 --cont 64K --summary --inc-empty

--8<--
anon-thp-aligned-16kB:                16 kB ( 0%)
anon-thp-aligned-32kB:                 0 kB ( 0%)
anon-thp-aligned-64kB:           4194304 kB (100%)
anon-thp-aligned-128kB:                0 kB ( 0%)
anon-thp-aligned-256kB:                0 kB ( 0%)
anon-thp-aligned-512kB:                0 kB ( 0%)
anon-thp-aligned-1024kB:               0 kB ( 0%)
anon-thp-aligned-2048kB:               0 kB ( 0%)
anon-thp-unaligned-16kB:               0 kB ( 0%)
anon-thp-unaligned-32kB:               0 kB ( 0%)
anon-thp-unaligned-64kB:               0 kB ( 0%)
anon-thp-unaligned-128kB:              0 kB ( 0%)
anon-thp-unaligned-256kB:              0 kB ( 0%)
anon-thp-unaligned-512kB:              0 kB ( 0%)
anon-thp-unaligned-1024kB:             0 kB ( 0%)
anon-thp-unaligned-2048kB:             0 kB ( 0%)
anon-thp-partial:                      0 kB ( 0%)
file-thp-aligned-16kB:                16 kB ( 1%)
file-thp-aligned-32kB:                64 kB ( 5%)
file-thp-aligned-64kB:               640 kB (50%)
file-thp-aligned-128kB:              128 kB (10%)
file-thp-aligned-256kB:                0 kB ( 0%)
file-thp-aligned-512kB:                0 kB ( 0%)
file-thp-aligned-1024kB:               0 kB ( 0%)
file-thp-aligned-2048kB:               0 kB ( 0%)
file-thp-unaligned-16kB:              16 kB ( 1%)
file-thp-unaligned-32kB:              32 kB ( 3%)
file-thp-unaligned-64kB:              64 kB ( 5%)
file-thp-unaligned-128kB:              0 kB ( 0%)
file-thp-unaligned-256kB:              0 kB ( 0%)
file-thp-unaligned-512kB:              0 kB ( 0%)
file-thp-unaligned-1024kB:             0 kB ( 0%)
file-thp-unaligned-2048kB:             0 kB ( 0%)
file-thp-partial:                     12 kB ( 1%)
anon-cont-aligned-64kB:          4194304 kB (100%)
file-cont-aligned-64kB:              768 kB (61%)
--8<--

Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>