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] [--rollup]
               [--cont size[KMG]] [--inc-smaps] [--inc-empty]
               [--periodic sleep_ms]

Prints information about how transparent huge pages are mapped, either
system-wide, or for a specified process or cgroup.

When run with --pid, the user explicitly specifies the set of pids to
scan.  e.g.  "--pid 10 [--pid 134 ...]".  When run with --cgroup, the user
passes either a v1 or v2 cgroup and all pids that belong to the cgroup
subtree are scanned.  When run with neither --pid nor --cgroup, the full
set of pids on the system is gathered from /proc and scanned as if the
user had provided "--pid 1 --pid 2 ...".

A default set of statistics is always generated for THP mappings. 
However, it is also possible to generate additional statistics for
"contiguous block mappings" where the block size is user-defined.

Statistics are maintained independently for anonymous and file-backed
(pagecache) memory and are shown both in kB and as a percentage of either
total anonymous or total file-backed memory as appropriate.

THP Statistics
--------------

Statistics are always generated for fully- and contiguously-mapped THPs
whose mapping address is aligned to their size, for each <size> supported
by the system.  Separate counters describe THPs mapped by PTE vs those
mapped by PMD.  (Although note a THP can only be mapped by PMD if it is
PMD-sized):

- anon-thp-pte-aligned-<size>kB
- file-thp-pte-aligned-<size>kB
- anon-thp-pmd-aligned-<size>kB
- file-thp-pmd-aligned-<size>kB

Similarly, statistics are always generated for fully- and contiguously-
mapped THPs whose mapping address is *not* aligned to their size, for each
<size> supported by the system.  Due to the unaligned mapping, it is
impossible to map by PMD, so there are only PTE counters for this case:

- anon-thp-pte-unaligned-<size>kB
- file-thp-pte-unaligned-<size>kB

Statistics are also always generated for mapped pages that belong to a THP
but where the is THP is *not* fully- and contiguously- mapped.  These
"partial" mappings are all counted in the same counter regardless of the
size of the THP that is partially mapped:

- anon-thp-pte-partial
- file-thp-pte-partial

Contiguous Block Statistics
---------------------------

An optional, additional set of statistics is generated for every
contiguous block size specified with `--cont <size>`.  These statistics
show how much memory is mapped in contiguous blocks of <size> and also
aligned to <size>.  A given contiguous block must all belong to the same
THP, but there is no requirement for it to be the *whole* THP.  Separate
counters describe contiguous blocks mapped by PTE vs those mapped by PMD:

- anon-cont-pte-aligned-<size>kB
- file-cont-pte-aligned-<size>kB
- anon-cont-pmd-aligned-<size>kB
- file-cont-pmd-aligned-<size>kB

As an example, if monitoring 64K contiguous blocks (--cont 64K), there are
a number of sources that could provide such blocks: a fully- and
contiguously-mapped 64K THP that is aligned to a 64K boundary would
provide 1 block.  A fully- and contiguously-mapped 128K THP that is
aligned to at least a 64K boundary would provide 2 blocks.  Or a 128K THP
that maps its first 100K, but contiguously and starting at a 64K boundary
would provide 1 block.  A fully- and contiguously-mapped 2M THP would
provide 32 blocks.  There are many other possible permutations.

options:
  -h, --help           show this help message and exit
  --pid pid            Process id of the target process. Maybe issued
                       multiple times to scan multiple processes. --pid
                       and --cgroup are mutually exclusive. If neither
                       are provided, all processes are scanned to
                       provide system-wide information.
  --cgroup path        Path to the target cgroup in sysfs. Iterates
                       over every pid in the cgroup and its children.
                       --pid and --cgroup are mutually exclusive. If
                       neither are provided, all processes are scanned
                       to provide system-wide information.
  --rollup             Sum the per-vma statistics to provide a summary
                       over the whole system, process or cgroup.
  --cont size[KMG]     Adds stats for memory that is mapped in
                       contiguous blocks of <size> and also aligned to
                       <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 all processes in the system
(--inc-empty forces printing stats that are 0):

    # ./thpmaps --cont 64K --rollup --inc-empty

--8<--
anon-thp-pmd-aligned-2048kB:      139264 kB ( 6%)
file-thp-pmd-aligned-2048kB:           0 kB ( 0%)
anon-thp-pte-aligned-16kB:             0 kB ( 0%)
anon-thp-pte-aligned-32kB:             0 kB ( 0%)
anon-thp-pte-aligned-64kB:         72256 kB ( 3%)
anon-thp-pte-aligned-128kB:            0 kB ( 0%)
anon-thp-pte-aligned-256kB:            0 kB ( 0%)
anon-thp-pte-aligned-512kB:            0 kB ( 0%)
anon-thp-pte-aligned-1024kB:           0 kB ( 0%)
anon-thp-pte-aligned-2048kB:           0 kB ( 0%)
anon-thp-pte-unaligned-16kB:           0 kB ( 0%)
anon-thp-pte-unaligned-32kB:           0 kB ( 0%)
anon-thp-pte-unaligned-64kB:           0 kB ( 0%)
anon-thp-pte-unaligned-128kB:          0 kB ( 0%)
anon-thp-pte-unaligned-256kB:          0 kB ( 0%)
anon-thp-pte-unaligned-512kB:          0 kB ( 0%)
anon-thp-pte-unaligned-1024kB:         0 kB ( 0%)
anon-thp-pte-unaligned-2048kB:         0 kB ( 0%)
anon-thp-pte-partial:              63232 kB ( 3%)
file-thp-pte-aligned-16kB:        809024 kB (47%)
file-thp-pte-aligned-32kB:         43168 kB ( 3%)
file-thp-pte-aligned-64kB:         98496 kB ( 6%)
file-thp-pte-aligned-128kB:        17536 kB ( 1%)
file-thp-pte-aligned-256kB:            0 kB ( 0%)
file-thp-pte-aligned-512kB:            0 kB ( 0%)
file-thp-pte-aligned-1024kB:           0 kB ( 0%)
file-thp-pte-aligned-2048kB:           0 kB ( 0%)
file-thp-pte-unaligned-16kB:       21712 kB ( 1%)
file-thp-pte-unaligned-32kB:         704 kB ( 0%)
file-thp-pte-unaligned-64kB:         896 kB ( 0%)
file-thp-pte-unaligned-128kB:      44928 kB ( 3%)
file-thp-pte-unaligned-256kB:          0 kB ( 0%)
file-thp-pte-unaligned-512kB:          0 kB ( 0%)
file-thp-pte-unaligned-1024kB:         0 kB ( 0%)
file-thp-pte-unaligned-2048kB:         0 kB ( 0%)
file-thp-pte-partial:               9252 kB ( 1%)
anon-cont-pmd-aligned-64kB:       139264 kB ( 6%)
file-cont-pmd-aligned-64kB:            0 kB ( 0%)
anon-cont-pte-aligned-64kB:       100672 kB ( 4%)
file-cont-pte-aligned-64kB:       161856 kB ( 9%)
--8<--

Link: https://lkml.kernel.org/r/20240116141235.960842-1-ryan.roberts@arm.comSigned-off-by: Ryan Roberts <ryan.roberts@arm.com>
Tested-by: Barry Song <v-songbaohua@oppo.com>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: William Kucharski <william.kucharski@oracle.com>
Cc: Zenghui Yu <yuzenghui@huawei.com>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>