Add a new DAMOS action, DAMOS_SPLIT, that splits large folios in the target region down to a smaller order. A new per-scheme field and sysfs file, target_order, selects the split target: 0 for order-0 base pages, or 2..HPAGE_PMD_ORDER-1 for a smaller mTHP order (order-1 is rejected at store time since anonymous THPs cannot be split to order-1).
Unlike DAMOS_COLLAPSE which builds large folios, splitting only dismantles them; it allocates nothing, copies nothing, and no THP admission policy applies. khugepaged deliberately refuses to collapse a folio to a smaller order, leaving the shrink direction to callers like this one. This patch adds the DAMOS_SPLIT action, the ``order`` field (placed in the existing union alongside target_nid and migrate_dests), its sysfs interface, and documentation. The vaddr operations set handler is added in the next patch. Link: https://lore.kernel.org/[email protected]/ ("mm/khugepaged: skip collapsing mTHP to smaller orders") Co-developed-by: Kunwu Chan <[email protected]> Signed-off-by: Kunwu Chan <[email protected]> Signed-off-by: Lian Wang (Processmission) <[email protected]> --- .../ABI/testing/sysfs-kernel-mm-damon | 7 +++ Documentation/mm/damon/design.rst | 5 ++ include/linux/damon.h | 15 ++++-- mm/damon/core.c | 2 + mm/damon/sysfs-schemes.c | 48 +++++++++++++++++++ tools/testing/selftests/damon/sysfs.py | 11 +++-- 6 files changed, 79 insertions(+), 9 deletions(-) diff --git a/Documentation/ABI/testing/sysfs-kernel-mm-damon b/Documentation/ABI/testing/sysfs-kernel-mm-damon index 907a504fb64c..ee8e260a631c 100644 --- a/Documentation/ABI/testing/sysfs-kernel-mm-damon +++ b/Documentation/ABI/testing/sysfs-kernel-mm-damon @@ -265,6 +265,13 @@ Contact: SJ Park <[email protected]> Description: Action's target NUMA node id. Supported by only relevant actions. +What: /sys/kernel/mm/damon/admin/kdamonds/<K>/contexts/<C>/schemes/<S>/target_order +Date: Jul 2026 +Contact: SJ Park <[email protected]> +Description: Target folio order for the ``split`` action. Large folios in + the target region are split down to this order. Valid values + are 0 (order-0 base pages) and 2..HPAGE_PMD_ORDER-1. + What: /sys/kernel/mm/damon/admin/kdamonds/<K>/contexts/<C>/schemes/<S>/apply_interval_us Date: Sep 2023 Contact: SJ Park <[email protected]> diff --git a/Documentation/mm/damon/design.rst b/Documentation/mm/damon/design.rst index aed6cb1cf483..87a801954b1b 100644 --- a/Documentation/mm/damon/design.rst +++ b/Documentation/mm/damon/design.rst @@ -549,6 +549,11 @@ that supports each action are as below. Supported by ``vaddr`` and ``fvaddr`` operations set. When TRANSPARENT_HUGEPAGE is disabled, the application of the action will just fail. + - ``split``: Split each large folio in the region down to the order specified + by the scheme's ``target_order`` (``0`` for order-0 base pages, or + ``2..HPAGE_PMD_ORDER-1``). Supported by ``vaddr`` and ``fvaddr`` operations + set. When TRANSPARENT_HUGEPAGE is disabled, the application of the action + will just fail. - ``lru_prio``: Prioritize the region on its LRU lists. Supported by ``paddr`` operations set. - ``lru_deprio``: Deprioritize the region on its LRU lists. diff --git a/include/linux/damon.h b/include/linux/damon.h index f69442a9d431..88b61b900a36 100644 --- a/include/linux/damon.h +++ b/include/linux/damon.h @@ -110,6 +110,7 @@ struct damon_target { * @DAMOS_HUGEPAGE: Call ``madvise()`` for the region with MADV_HUGEPAGE. * @DAMOS_NOHUGEPAGE: Call ``madvise()`` for the region with MADV_NOHUGEPAGE. * @DAMOS_COLLAPSE: Call ``madvise()`` for the region with MADV_COLLAPSE. + * @DAMOS_SPLIT: Split each large folio in the region to a smaller order. * @DAMOS_LRU_PRIO: Prioritize the region on its LRU lists. * @DAMOS_LRU_DEPRIO: Deprioritize the region on its LRU lists. * @DAMOS_MIGRATE_HOT: Migrate the regions prioritizing warmer regions. @@ -130,6 +131,7 @@ enum damos_action { DAMOS_HUGEPAGE, DAMOS_NOHUGEPAGE, DAMOS_COLLAPSE, + DAMOS_SPLIT, DAMOS_LRU_PRIO, DAMOS_LRU_DEPRIO, DAMOS_MIGRATE_HOT, @@ -582,10 +584,15 @@ struct damos { struct damos_quota quota; struct damos_watermarks wmarks; union { - struct { - int target_nid; - struct damos_migrate_dests migrate_dests; - }; + int target_nid; + struct damos_migrate_dests migrate_dests; + /* + * @order: target folio order for DAMOS_SPLIT. + * Split large folios down to this order. 0 for + * order-0 base pages, 2..HPAGE_PMD_ORDER-1 for + * smaller mTHP. Order-1 is rejected. + */ + unsigned int order; }; struct list_head core_filters; struct list_head ops_filters; diff --git a/mm/damon/core.c b/mm/damon/core.c index 806a67d02a6e..394c62455ad5 100644 --- a/mm/damon/core.c +++ b/mm/damon/core.c @@ -693,6 +693,7 @@ struct damos *damon_new_scheme(struct damos_access_pattern *pattern, return NULL; scheme->pattern = *pattern; scheme->action = action; + scheme->order = 0; scheme->apply_interval_us = apply_interval_us; /* * next_apply_sis will be set when kdamond starts. While kdamond is @@ -1446,6 +1447,7 @@ static int damos_commit(struct damos *dst, struct damos *src) dst->pattern = src->pattern; dst->action = src->action; + dst->order = src->order; dst->apply_interval_us = src->apply_interval_us; err = damos_commit_quota(&dst->quota, &src->quota); diff --git a/mm/damon/sysfs-schemes.c b/mm/damon/sysfs-schemes.c index 32f495a96b17..725ed81ccf6c 100644 --- a/mm/damon/sysfs-schemes.c +++ b/mm/damon/sysfs-schemes.c @@ -4,7 +4,9 @@ */ #include <linux/slab.h> +#include <linux/mm.h> #include <linux/numa.h> +#include <linux/huge_mm.h> #include "sysfs-common.h" @@ -2260,6 +2262,7 @@ struct damon_sysfs_scheme { struct damon_sysfs_stats *stats; struct damon_sysfs_scheme_regions *tried_regions; int target_nid; + unsigned int target_order; struct damos_sysfs_dests *dests; }; @@ -2293,6 +2296,10 @@ static struct damos_sysfs_action_name damos_sysfs_action_names[] = { .action = DAMOS_COLLAPSE, .name = "collapse", }, + { + .action = DAMOS_SPLIT, + .name = "split", + }, { .action = DAMOS_LRU_PRIO, .name = "lru_prio", @@ -2326,6 +2333,7 @@ static struct damon_sysfs_scheme *damon_sysfs_scheme_alloc( scheme->action = action; scheme->apply_interval_us = apply_interval_us; scheme->target_nid = NUMA_NO_NODE; + scheme->target_order = 0; return scheme; } @@ -2645,6 +2653,40 @@ static ssize_t target_nid_store(struct kobject *kobj, return err ? err : count; } +static ssize_t target_order_show(struct kobject *kobj, + struct kobj_attribute *attr, char *buf) +{ + struct damon_sysfs_scheme *scheme = container_of(kobj, + struct damon_sysfs_scheme, kobj); + + return sysfs_emit(buf, "%u\n", scheme->target_order); +} + +static ssize_t target_order_store(struct kobject *kobj, + struct kobj_attribute *attr, const char *buf, size_t count) +{ + struct damon_sysfs_scheme *scheme = container_of(kobj, + struct damon_sysfs_scheme, kobj); + unsigned int val; + int err; + + err = kstrtouint(buf, 0, &val); + if (err) + return err; + +#ifdef CONFIG_TRANSPARENT_HUGEPAGE + /* Valid split targets: 0 (order-0 base pages) or 2..HPAGE_PMD_ORDER-1. */ + if (val != 0 && (val < 2 || val >= HPAGE_PMD_ORDER)) + return -EINVAL; +#else + if (val != 0) + return -EINVAL; +#endif + + scheme->target_order = val; + return count; +} + static void damon_sysfs_scheme_release(struct kobject *kobj) { kfree(container_of(kobj, struct damon_sysfs_scheme, kobj)); @@ -2659,10 +2701,14 @@ static struct kobj_attribute damon_sysfs_scheme_apply_interval_us_attr = static struct kobj_attribute damon_sysfs_scheme_target_nid_attr = __ATTR_RW_MODE(target_nid, 0600); +static struct kobj_attribute damon_sysfs_scheme_target_order_attr = + __ATTR_RW_MODE(target_order, 0600); + static struct attribute *damon_sysfs_scheme_attrs[] = { &damon_sysfs_scheme_action_attr.attr, &damon_sysfs_scheme_apply_interval_us_attr.attr, &damon_sysfs_scheme_target_nid_attr.attr, + &damon_sysfs_scheme_target_order_attr.attr, NULL, }; ATTRIBUTE_GROUPS(damon_sysfs_scheme); @@ -3011,6 +3057,8 @@ static struct damos *damon_sysfs_mk_scheme( if (!scheme) return NULL; + scheme->order = sysfs_scheme->target_order; + err = damos_sysfs_add_quota_score(sysfs_quotas->goals, &scheme->quota); if (err) { damon_destroy_scheme(scheme); diff --git a/tools/testing/selftests/damon/sysfs.py b/tools/testing/selftests/damon/sysfs.py index 3ffa054b6386..49d3c319dfd8 100755 --- a/tools/testing/selftests/damon/sysfs.py +++ b/tools/testing/selftests/damon/sysfs.py @@ -131,11 +131,12 @@ def assert_scheme_committed(scheme, dump): 'hugepage': 3, 'nohugepage': 4, 'collapse': 5, - 'lru_prio': 6, - 'lru_deprio': 7, - 'migrate_hot': 8, - 'migrate_cold': 9, - 'stat': 10, + 'split': 6, + 'lru_prio': 7, + 'lru_deprio': 8, + 'migrate_hot': 9, + 'migrate_cold': 10, + 'stat': 11, } assert_true(dump['action'] == action_val[scheme.action], 'action', dump) assert_true(dump['apply_interval_us'] == scheme. apply_interval_us,
