* Re: [RESEND RFC PATCH v2 4/5] mm/damon: introduce DAMOS_SPLIT action
[not found] <20260702094633.75658-5-lianux.mm@gmail.com>
@ 2026-07-02 20:00 ` SJ Park
0 siblings, 0 replies; only message in thread
From: SJ Park @ 2026-07-02 20:00 UTC (permalink / raw)
To: Lian Wang; +Cc: SJ Park, damon, linux-mm, daichaobing, kunwu.chan
On Thu, 2 Jul 2026 17:46:32 +0800 Lian Wang <lianux.mm@gmail.com> wrote:
> Add DAMOS_SPLIT to the damos_action enum for splitting large folios
> into smaller mTHP-order folios. Add a target_order field to struct
> damos to specify the desired split order.
This commit is not adding but reusing the field.
>
> Expose the action as "split" through the DAMON sysfs interface with
> target_order validation (must be 2..HPAGE_PMD_ORDER-1).
>
> Signed-off-by: Lian Wang <lianux.mm@gmail.com>
> Signed-off-by: Lian Wang <lianux.wang@processmission.com>
Let's have only one S-o-b: line if there is no reason to have two.
> ---
> include/linux/damon.h | 9 +++++++--
> mm/damon/sysfs-schemes.c | 16 ++++++++++++++++
> 2 files changed, 23 insertions(+), 2 deletions(-)
>
> diff --git a/include/linux/damon.h b/include/linux/damon.h
> index 5a0587556573..30cf4afb212c 100644
> --- a/include/linux/damon.h
> +++ b/include/linux/damon.h
> @@ -121,6 +121,7 @@ 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 large folios to the target mTHP 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.
> @@ -141,6 +142,7 @@ enum damos_action {
> DAMOS_HUGEPAGE,
> DAMOS_NOHUGEPAGE,
> DAMOS_COLLAPSE,
> + DAMOS_SPLIT,
> DAMOS_LRU_PRIO,
> DAMOS_LRU_DEPRIO,
> DAMOS_MIGRATE_HOT,
> @@ -573,8 +575,11 @@ struct damos {
> struct damos_access_pattern pattern;
> enum damos_action action;
> /*
> - * @target_order: target order for mTHP actions (DAMOS_COLLAPSE).
> - * 0 means system default (PMD order). Valid: 0, 2..HPAGE_PMD_ORDER.
> + * @target_order: target mTHP order for DAMOS_COLLAPSE and
> + * DAMOS_SPLIT. For COLLAPSE, 0 means PMD order default,
> + * valid values: 0, 2..HPAGE_PMD_ORDER. For SPLIT,
> + * valid values: 2..HPAGE_PMD_ORDER-1; 0 and HPAGE_PMD_ORDER
> + * are rejected at scheme creation time (defaulting to 2).
> */
> unsigned int target_order;
As I commented to an earlier patch, let's use the union.
> unsigned long apply_interval_us;
> diff --git a/mm/damon/sysfs-schemes.c b/mm/damon/sysfs-schemes.c
> index 7dcd582ded86..84a4617ca3d3 100644
> --- a/mm/damon/sysfs-schemes.c
> +++ b/mm/damon/sysfs-schemes.c
> @@ -2293,6 +2293,10 @@ 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",
> @@ -3058,11 +3062,23 @@ static struct damos *damon_sysfs_mk_scheme(
> HPAGE_PMD_ORDER, HPAGE_PMD_ORDER);
> target_order = 0;
> }
> + if (sysfs_scheme->action == DAMOS_SPLIT &&
> + (target_order == 0 ||
> + target_order >= HPAGE_PMD_ORDER)) {
> + pr_warn("DAMON split: target_order %u invalid, need 2..%u. Defaulting to 2.\n",
> + target_order,
> + HPAGE_PMD_ORDER - 1);
> + target_order = 2;
> + }
As I also commented to an earlier patch, this validation will eventually
dropped.
> #else
> if (sysfs_scheme->action == DAMOS_COLLAPSE && target_order != 0) {
> pr_warn("DAMON collapse: target_order not supported without THP. Use 0.\n");
> target_order = 0;
> }
> + if (sysfs_scheme->action == DAMOS_SPLIT) {
> + pr_warn("DAMON split: not supported without THP.\n");
> + target_order = 2;
Why set target_order here?
> + }
> #endif
> scheme->target_order = target_order;
Thanks,
SJ
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