mm/damon: introduce hugepage_size probe filter

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 \
                --probe_prep set_pgidle --probe_filter allow pgidle_unset \
                --probe_weight 1 \
            --probe \
                --probe_filter allow hugepage_size 2M 2M

Show the monitoring results.

    $ sudo ./damo report attrs
    heatmap: 000000000003[...]666666666666666666666666666666666666666666666668888888888888988888888[...]8
    # min/max temperatures: -2,770,000,000, 68,474,934, column size: 69.784 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   250.805 MiB  86.185 TiB    27.700 s      0 0
    1   556.285 MiB  86.184 TiB    27.400 s      0 0
    2   1.629 GiB    127.488 TiB   8.500 s       0 4
    3   535.770 MiB  127.490 TiB   8.400 s       0 7
    4   1.066 GiB    127.490 TiB   8.200 s       0 6
    5   501.332 MiB  127.492 TiB   600 ms        0 12
    [...]
    50  146.133 MiB  127.492 TiB   200 ms        2 20
    51  16.000 KiB   127.492 TiB   200 ms        11 20
    52  144.000 KiB  127.492 TiB   200 ms        17 20
    53  48.000 KiB   127.492 TiB   200 ms        18 20
    54  1.930 MiB    127.492 TiB   200 ms        19 20
    [...]
    101 1.996 MiB    127.492 TiB   2.100 s       1 20
    102 1.992 MiB    127.492 TiB   2.100 s       20 20
    103 1.984 MiB    127.492 TiB   2.200 s       1 20
    104 2.000 MiB    127.492 TiB   2.300 s       20 20
    105 2.000 MiB    127.492 TiB   2.600 s       20 20
    memory bw estimate: 0 B per second
    total size: 5.452 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 region is sorted by access temperature, which is a weighted sum of the first probe_hits count and the age. That is, regions at the beginning of the list are colder than those at the end of the list. The second probe_hits count shows the ratio of 2 MiB hugepages in the region.

For example, region 5, which has 501.332 MiB size, has not accessed for the last 600 milliseconds and uses 2 MiB THP for ~60% (12/20) of the region.

Region 105, which is 2 MiB size, has been accessed at least 20 times per 100 milliseconds for the last 2.6 seconds) and fully backed by 2 MiB hugepage.

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

Changes from RFC v3
- RFC v3: https://lore.kernel.org/[email protected]
- Drop RFC tag.
- Rebase to lastes mm-new.
Changes from RFC v2
- RFC v2: https://lore.kernel.org/[email protected]
- Free new filter for invalid filter commit case.
Changes from RFC
- RFC: https://lore.kernel.org/[email protected]
- Commit size range for newly added hugepage_size filter.
- Rebase to latest mm-new.

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                               | 28 ++++++++--
 mm/damon/ops-common.c                         | 10 ++++
 mm/damon/sysfs.c                              | 55 +++++++++++++++++++
 7 files changed, 115 insertions(+), 6 deletions(-)

base-commit: c93300483b699bbc752f1000a1309e8fcf2c9fb2

2.47.3

Introduce a new data attribute probe filter type, hugepage_size. It will work for memory that is backed by a hugepage of a given size range. Add a new damon_filter_type enum DAMON_FILTER_TYPE_HUGEPAGE_SIZE to identify the type. Add two new fields in the damon_filter struct for saving the size range.

---
 include/linux/damon.h | 8 ++++++++
 1 file changed, 8 insertions(+)

index 4be7d1df8e71f..bbb190b474015 100644
@@ -783,12 +783,14 @@ struct damon_prep {
  * @DAMON_FILTER_TYPE_MEMCG:		Specific memcg's pages.
  * @DAMON_FILTER_TYPE_PGIDLE_UNSET:	Pgidle is unset.
  * @DAMON_FILTER_TYPE_PGIDLE_SET:	Pgidle is set.
+ * @DAMON_FILTER_TYPE_HUGEPAGE_SIZE:	Page is part of a hugepage.
  */
 enum damon_filter_type {
 	DAMON_FILTER_TYPE_ANON,
 	DAMON_FILTER_TYPE_MEMCG,
 	DAMON_FILTER_TYPE_PGIDLE_UNSET,
 	DAMON_FILTER_TYPE_PGIDLE_SET,
+	DAMON_FILTER_TYPE_HUGEPAGE_SIZE,
 };
 
 /**

@@ -798,6 +800,8 @@ enum damon_filter_type {
  * @matching:	Whether this filter is for the type-matching ones.
  * @allow:	Whether the @type-@matching ones should pass this filter.
  * @memcg_id:	Memcg id of the question if @type is DAMON_FILTER_MEMCG.
+ * @range_min:	Minimum value of range arguments.
+ * @range_max:	Maximum value of range arguments.
  */
 struct damon_filter {
 	enum damon_filter_type type;

@@ -805,6 +809,10 @@ struct damon_filter {
 	bool allow;
 	union {
 		u64 memcg_id;
+		struct {
+			unsigned long range_min;
+			unsigned long range_max;
+		};
 	};
 /* private: */
 	/* Siblings list. */

2.47.3

Extend data attribute probe filters commit logic for the new hugepage_size filter type. Since it needs to carry the size range of the hugepage, update the logic to update the size range fields of the commit destination filter struct. While doing that, validate the given range and propagate an error if it is invalid. Add the error handling in the callers, too.

---
 mm/damon/core.c | 28 +++++++++++++++++++++++-----
 1 file changed, 23 insertions(+), 5 deletions(-)

index e0414d2adcb41..dd4317df42ff4 100644
@@ -1818,7 +1818,7 @@ static int damon_commit_preps(struct damon_probe *dst, struct damon_probe *src)
 	return 0;
 }
 
-static void damon_commit_filter(struct damon_filter *dst,
+static int damon_commit_filter(struct damon_filter *dst,
 		struct damon_filter *src)
 {
 	dst->type = src->type;

@@ -1828,23 +1828,33 @@ static void damon_commit_filter(struct damon_filter *dst,
 	case DAMON_FILTER_TYPE_MEMCG:
 		dst->memcg_id = src->memcg_id;
 		break;
+	case DAMON_FILTER_TYPE_HUGEPAGE_SIZE:
+		if (src->range_max < src->range_min)
+			return -EINVAL;
+		dst->range_min = src->range_min;
+		dst->range_max = src->range_max;
+		break;
 	default:
 		break;
 	}
+	return 0;
 }
 
 static int damon_commit_filters(struct damon_probe *dst,
 		struct damon_probe *src)
 {
 	struct damon_filter *dst_filter, *next, *src_filter, *new_filter;
-	int i = 0, j = 0;
+	int i = 0, j = 0, err;
 
 	damon_for_each_filter_safe(dst_filter, next, dst) {
 		src_filter = damon_nth_filter(i++, src);
-		if (src_filter)
-			damon_commit_filter(dst_filter, src_filter);
-		else
+		if (src_filter) {
+			err = damon_commit_filter(dst_filter, src_filter);
+			if (err)
+				return err;
+		} else {
 			damon_destroy_filter(dst_filter);
+		}
 	}
 
 	damon_for_each_filter_safe(src_filter, next, src) {

@@ -1859,6 +1869,14 @@ static int damon_commit_filters(struct damon_probe *dst,
 		case DAMON_FILTER_TYPE_MEMCG:
 			new_filter->memcg_id = src_filter->memcg_id;
 			break;
+		case DAMON_FILTER_TYPE_HUGEPAGE_SIZE:
+			if (src_filter->range_max < src_filter->range_min) {
+				damon_destroy_filter(new_filter);
+				return -EINVAL;
+			}
+			new_filter->range_min = src_filter->range_min;
+			new_filter->range_max = src_filter->range_max;
+			break;
 		default:
 			break;
 		}

2.47.3

Update ops-common data attribute filter matching logic to support hugepage_size filter type.

---
 mm/damon/ops-common.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

index c36cc39cd2c70..77366f42b3e5b 100644
@@ -536,6 +536,7 @@ bool damon_ops_filter_match(struct damon_filter *filter, struct folio *folio)
 {
 	bool matched = false;
 	struct mem_cgroup *memcg;
+	size_t folio_sz;
 
 	switch (filter->type) {
 	case DAMON_FILTER_TYPE_ANON:

@@ -558,6 +559,15 @@ bool damon_ops_filter_match(struct damon_filter *filter, struct folio *folio)
 			matched = filter->memcg_id == mem_cgroup_id(memcg);
 		rcu_read_unlock();
 		break;
+	case DAMON_FILTER_TYPE_HUGEPAGE_SIZE:
+		if (!folio) {
+			matched = false;
+			break;
+		}
+		folio_sz = folio_size(folio);
+		matched = filter->range_min <= folio_sz &&
+			folio_sz <= filter->range_max;
+		break;
 	default:
 		break;
 	}

2.47.3

In future, DAMON sysfs interface will support data attribute probe filter types that have range arguments like the newly added hugepage_size type filter. To prepare such supports, add two new DAMON sysfs files, min and max, under the probe filter directory.

---
 mm/damon/sysfs.c | 48 ++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 48 insertions(+)

index 51fa506c879b0..8e8d89b8ed981 100644
@@ -975,6 +975,8 @@ struct damon_sysfs_filter {
 	bool matching;
 	bool allow;
 	char *path;
+	unsigned long range_min;
+	unsigned long range_max;
 };
 
 static struct damon_sysfs_filter *damon_sysfs_filter_alloc(void)

@@ -1127,6 +1129,44 @@ static ssize_t path_store(struct kobject *kobj,
 	return count;
 }
 
+static ssize_t min_show(struct kobject *kobj,
+		struct kobj_attribute *attr, char *buf)
+{
+	struct damon_sysfs_filter *filter = container_of(kobj,
+			struct damon_sysfs_filter, kobj);
+
+	return sysfs_emit(buf, "%lu\n", filter->range_min);
+}
+
+static ssize_t min_store(struct kobject *kobj,
+		struct kobj_attribute *attr, const char *buf, size_t count)
+{
+	struct damon_sysfs_filter *filter = container_of(kobj,
+			struct damon_sysfs_filter, kobj);
+	int err = kstrtoul(buf, 0, &filter->range_min);
+
+	return err ? err : count;
+}
+
+static ssize_t max_show(struct kobject *kobj,
+		struct kobj_attribute *attr, char *buf)
+{
+	struct damon_sysfs_filter *filter = container_of(kobj,
+			struct damon_sysfs_filter, kobj);
+
+	return sysfs_emit(buf, "%lu\n", filter->range_max);
+}
+
+static ssize_t max_store(struct kobject *kobj,
+		struct kobj_attribute *attr, const char *buf, size_t count)
+{
+	struct damon_sysfs_filter *filter = container_of(kobj,
+			struct damon_sysfs_filter, kobj);
+	int err = kstrtoul(buf, 0, &filter->range_max);
+
+	return err ? err : count;
+}
+
 static void damon_sysfs_filter_release(struct kobject *kobj)
 {
 	struct damon_sysfs_filter *filter = container_of(kobj,

@@ -1148,11 +1188,19 @@ static struct kobj_attribute damon_sysfs_filter_allow_attr =
 static struct kobj_attribute damon_sysfs_filter_path_attr =
 		__ATTR_RW_MODE(path, 0600);
 
+static struct kobj_attribute damon_sysfs_filter_min_attr =
+		__ATTR_RW_MODE(min, 0600);
+
+static struct kobj_attribute damon_sysfs_filter_max_attr =
+		__ATTR_RW_MODE(max, 0600);
+
 static struct attribute *damon_sysfs_filter_attrs[] = {
 	&damon_sysfs_filter_type_attr.attr,
 	&damon_sysfs_filter_matching_attr.attr,
 	&damon_sysfs_filter_allow_attr.attr,
 	&damon_sysfs_filter_path_attr.attr,
+	&damon_sysfs_filter_min_attr.attr,
+	&damon_sysfs_filter_max_attr.attr,
 	NULL,
 };
 ATTRIBUTE_GROUPS(damon_sysfs_filter);

2.47.3

Extend DAMON sysfs interface to support hugepage_size probe filter. Allows hugepage_size user string input to the filter type file. Pass the size range argument that users set via min/max files under the probe filter directory to the DAMON core.

---
 mm/damon/sysfs.c | 7 +++++++
 1 file changed, 7 insertions(+)

index 8e8d89b8ed981..43519afb9eb7f 100644
@@ -1007,6 +1007,10 @@ damon_sysfs_filter_type_names[] = {
 		.type = DAMON_FILTER_TYPE_PGIDLE_SET,
 		.name = "pgidle_set",
 	},
+	{
+		.type = DAMON_FILTER_TYPE_HUGEPAGE_SIZE,
+		.name = "hugepage_size",
+	},
 };
 
 static ssize_t type_show(struct kobject *kobj,

@@ -2273,6 +2277,9 @@ static int damon_sysfs_set_filters(struct damon_probe *probe,
 				damon_destroy_filter(filter);
 				return err;
 			}
+		} else if (filter->type == DAMON_FILTER_TYPE_HUGEPAGE_SIZE) {
+			filter->range_min = sys_filter->range_min;
+			filter->range_max = sys_filter->range_max;
 		}
 		damon_add_filter(probe, filter);
 	}

2.47.3

Update DAMON design document for the newly added hugepage_size data attribute probe filter type.

---
 Documentation/mm/damon/design.rst | 2 ++
 1 file changed, 2 insertions(+)

index 707170bcd1b33..0a86792f90a18 100644
@@ -300,6 +300,8 @@ filter types.  Currently below filter types are supported.
 - ``pgidle_unset``: Matches if the page for the memory is marked as not
   access-idle.
 - ``pgidle_set``: Matches if the page for the memory is marked as access-idle.
+- ``hugepage_size``: Matches if the page for the memory is a part of a hugepage
+  of a given size range.
 
 If such probes are registered, DAMON executes the probes for each region's
 sampling memory when it does the access :ref:`sampling

2.47.3

Update DAMON usage document for the newly added hugepage_size data attribute filter type.

---
 Documentation/admin-guide/mm/damon/usage.rst | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

index d3e37400367bd..6b80bce5d678d 100644
@@ -78,7 +78,7 @@ comma (",").
     │ │ │ │ │ │ │ │ │ 0/prep_action
     │ │ │ │ │ │ │ │ │ ...
     │ │ │ │ │ │ │ │ filters/nr_filters
-    │ │ │ │ │ │ │ │ │ 0/type,matching,allow,path
+    │ │ │ │ │ │ │ │ │ 0/type,matching,allow,path,min,max
     │ │ │ │ │ │ │ │ │ ...
     │ │ │ │ │ │ │ ...
     │ │ │ │ │ :ref:`targets <sysfs_targets>`/nr_targets

@@ -308,6 +308,8 @@ Writing a number (``N``) to the file creates the number of child directories
 named ``0`` to ``N-1``.  Each directory represents each filter and works in a
 way similar to that for :ref:`DAMOS filter <sysfs_filters>`.  When the filter
 ``type`` is ``memcg``, ``path`` file acts as ``memcg_path`` for :ref:`DAMOS
+filter <sysfs_filters>`.  When the filter ``type`` is ``hugepage_size``,
+``min`` and ``max`` files acts as files of the same names for :ref:`DAMOS
 filter <sysfs_filters>`.
 
 .. _sysfs_targets:

2.47.3

Good catch. It is too trivial to respin the series in my humble opinion. I will fix this later unless others do that in near future.

Thanks,
SJ

[...]

For the newly added hugepage_size data attribute probe filter, two new sysfs files are added for the size range. Update DAMON ABI document for the new files.

---
 Documentation/ABI/testing/sysfs-kernel-mm-damon | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

index ad21f58f3c912..55df688ea596f 100644
@@ -206,6 +206,20 @@ Description:	If 'memcg' is written to the 'type' file, writing to and
 		reading from this file sets and gets the path to the memory
 		cgroup of the interest.
 
+What:		/sys/kernel/mm/damon/admin/kdamonds/<K>/contexts/<C>/monitoring_attrs/probes/<P>/filters/<F>/min
+Date:		Sep 2026
+Contact:	SJ Park <[email protected]>
+Description:	If 'hugepage_size' is written to the 'type' file, writing to and
+		reading from this file sets and gets the minimum size of the
+		huge page of the interest.
+
+What:		/sys/kernel/mm/damon/admin/kdamonds/<K>/contexts/<C>/monitoring_attrs/probes/<P>/filters/<F>/max
+Date:		Sep 2026
+Contact:	SJ Park <[email protected]>
+Description:	If 'hugepage_size' is written to the 'type' file, writing to and
+		reading from this file sets and gets the maximum size of the
+		huge page of the interest.
+
 What:		/sys/kernel/mm/damon/admin/kdamonds/<K>/contexts/<C>/monitoring_attrs/probes/<P>/filters/<F>/matching
 Date:		May 2026
 Contact:	SJ Park <[email protected]>

2.47.3

Sashiko found no blocker for this series other than a grammartical error in a document of patch 7. It is too trivial to respin the series in my opinion. Andrew, could you please fix it together when you pick this, or let me know if you have a different opinion?

Sashiko send its findings to damon@ mailing list [1], and I reply those if anything needs to be clarified. Please refer to those for details.

[1] https://lore.kernel.org/damon/

Thanks,
SJ

[...]

All queued up, thanks. With a -fix for [7/8].

fyi, I'm always reluctant to include testing info in the permanent record. Because it's development-time info which becomes obsolete very quickly.

It isn't useful to someone who is reading the changelog in mainline in 2028 (or even Nov 2026) because the patchset will have had far more testing since these words were written.

It is of course very useful info but I suggest it be maintained below the "---", where all short-term development-time info is best maintained.

Agreed. I will do so for individual patches. For cover letters that don't have the "---" lines, I will add an informal note saying "please do not add below to the commit message". If you prefer, I could add "---" line on the cover letter instead of the informal note. Or, I could add the informal note below the manual "---" line, too. Let me know if you prefer that.

Thanks,
SJ

Hi Andrew,

Thank you! I found the -fix is in the mm.git as below:

'''

$ git show 81c69fbb4128
[...]
--- a/Documentation/admin-guide/mm/damon/usage.rst
+++ b/Documentation/admin-guide/mm/damon/usage.rst
@@ -309,7 +309,7 @@ named ``0`` to ``N-1``.  Each directory represents each filter and works in a
 way similar to that for :ref:`DAMOS filter <sysfs_filters>`.  When the filter
 ``type`` is ``memcg``, ``path`` file acts as ``memcg_path`` for :ref:`DAMOS
 filter <sysfs_filters>`.  When the filter ``type`` is ``hugepage_size``,
-``min`` and ``max`` files acts as files of the same names for :ref:`DAMOS
+``min`` and ``max`` file acts as files of the same names for :ref:`DAMOS
 filter <sysfs_filters>`.

.. _sysfs_targets:
'''

But, I think it is slightly wrong. The fix I requested is 's/files acts/files act/', but the committed fix is doing
's/files acts/file acts/'. Could you please fix it when you get a chance? Let me know if there is anything that I can help, too.

Thanks,
SJ

[...]