[RFC PATCH 0/8] mm/damon: introduce hugepage_size probe filter

[SJ Park <sj@kernel.org>]

Knowing whether a given memory is backed by a hugepage of specific size
is useful for efficient utilization of hugepages.  For easy monitoring
of the information, introduce a new data attribute probe filter type,
hugepage_size.  It works similar to the DAMOS filter of the same name.
It works for memory that is backed by a hugepage of a given size range.

Patch 1 introduces the new probe filter type to DAMON API and extends
related data structures.  Patch 2 updates probe filter commit logic to
handle the size range.  Patch 3 Updates the filtering logic to support
the new type.  Patch 4 adds new DAMON sysfs files for the size range.
Patch 5 updates DAMON sysfs interface to fully support the new filter
type.  Patches 6-8 updates design, usage and ABI documents for the new
feature.

Test
====

Set THP always and start a test workload using masim [1].

    $ echo always | sudo tee /sys/kernel/mm/transparent_hugepage/enabled
    $ ./masim.py run --config_file ./configs/stairs-500mb.cfg --repeat 10

Using the DAMON user-space tool, damo [2], start DAMON with two probes.
The primary probe monitors access.  The secondary probe monitors 2 MiB
sized hugepages.  The region adjustment weight is given to only the
primary probe.  That is, this setup is for showing access temperature
and additionally how many 2 MiB hugepages are being used for the region
of the access temperature.

    $ sudo ./damo start $(pidof masim) \
            --probe_prep set_pgidle --probe_filter allow pgidle_unset \
            --probe_filter allow hugepage_size 2M 2M --probe_weight 1 0 \
            --nr_probe_preps 1 0 --nr_probe_filters 1 1 --nr_probes 2

Show the monitoring results.

    $ sudo ./damo report attrs
    heatmap: 000004[...]666666668988888888888844444430000000000000000000000000000000000000000000014[...]8
    # min/max temperatures: -470,000,000, 10,000,500, column size: 64.119 MiB
    probes
    - prep: set_pgidle, filter: allow pgidle_unset (weight: 1)
    - allow hugepage_size [2.000 MiB, 2.000 MiB] (weight: 0)
    intervals: sample 5 ms aggr 100 ms (max probe hits 20)
    #   size         address       age           probe_hits
    0   354.039 MiB  85.833 TiB    4.700 s       0 0
    1   1.843 GiB    127.724 TiB   4.700 s       0 6
    2   936.781 MiB  127.726 TiB   4.600 s       0 16
    [...]
    25  44.000 KiB   127.723 TiB   0 ns          15 20
    26  11.492 MiB   127.723 TiB   0 ns          16 20
    27  2.160 MiB    127.723 TiB   0 ns          19 20
    [...]
    47  376.000 KiB  127.723 TiB   300 ms        1 20
    48  48.000 KiB   127.723 TiB   400 ms        2 20
    49  812.000 KiB  127.723 TiB   500 ms        9 20
    memory bw estimate: 0 B per second
    total size: 5.009 GiB
    record DAMON intervals: sample 5 ms, aggr 100 ms

The first probe_hits count and the age show the access temperature of
each region.  The second probe_hits count shows the ratio of 2 MiB
hugepages in the region.

For example, region 2, which has 936 MiB size, is quite cold (not
accessed for 4.6 seconds) but uses 2 MiB THP for ~80% (16/20) of the
region.  Maybe not a very efficient use of THP.

On the other hand, region 49, which is 812 KiB size, is somewhat hot
(accessed about 9 times per 100 ms for the last 500 ms) and fully backed
by 2 MiB hugepage.  Maybe this is a good use of THP.

[1] https://github.com/sjp38/masim
[2] https://github.com/damonitor/damo

SJ Park (8):
  mm/damon/api: introduce DAMON_FILTER_TYPE_HUGEPAGE_SIZE
  mm/damon/core: commit hugepage_size type damon filter
  mm/damon/ops-common: support hugepage_size damon filter matching
  mm/damon/sysfs: add min,max files under probe filter directory
  mm/damon/sysfs: support hugepage_size probe filter
  Docs/mm/damon/design: update for hugepage_size probe filter
  Docs/admin-guide/mm/damon/usage: update for hugepage_size
  Docs/ABI/damon: update for hugepage_size probe filter

 .../ABI/testing/sysfs-kernel-mm-damon         | 14 +++++
 Documentation/admin-guide/mm/damon/usage.rst  |  4 +-
 Documentation/mm/damon/design.rst             |  2 +
 include/linux/damon.h                         |  8 +++
 mm/damon/core.c                               | 20 +++++--
 mm/damon/ops-common.c                         | 10 ++++
 mm/damon/sysfs.c                              | 55 +++++++++++++++++++
 7 files changed, 107 insertions(+), 6 deletions(-)


base-commit: 91c120b49e83b867e29684fd229c3e1f07190071
-- 
2.47.3