mm/damon/core: introduce damos_quota_goal->complement

Patch series "mm/damon: introduce damos quota goal target metric
complement flag".

Aim-oriented DAMOS quota auto-tuning assumes the aggressiveness of the
scheme (quota) and the quota goal metric are directly proportional. 
Depending on the scheme setup and usage, keeping the relationship can be
challenging.

For example, let's suppose a memory tiering approach for higher upper tier
utilization.  One common idea for that (TPP) is utilizing two schemes, one
for promotion and the other one for demotion.  The promotion scheme
migrates hot pages from lower tier to upper tier, aiming for high
utilization of the upper tier.  The demotion scheme migrates cold pages
from upper tier to lower tier, aiming for head room free memory of the
upper tier.  Both schemes and their goals are in direct proportion. 
However, for this kind of use case, we need to implement two different
goal metrics (per-node memory utilization and free memory ratio) while
essentially the free memory ratio is just a complemented value of the
utilization.

To avoid adding too many new metrics, we are adding metrics that turn out
to be really needed for each found use case.  For example,
some_mem_psi_us, node_eligible_mem_bp and hugepage_mem_bp don't have their
complemented value version.  But it is not really difficult to expect use
cases that their complemented version can be useful.  For example,
hugepage_mem_bp use case may need a way to reduce the hugepage ratio. 
That would require a complemented version of hugepage_mem_bp.  Adding a
new metric for each of such use cases could make the number of metrics
unnecessarily high, and discourage flexible usages of DAMOS.

Add a new flag, quota goal complement, to allow flexible tuning goal setup
without unnecessarily increasing the number of metrics.  The flag
specifies whether to use the complemented value of the given goal metric
for the tuning.  For example, if the complement flag is set, the upper
tier memory utilization ratio metric works the same as the free memory
ratio metric for the tier.


This patch (of 8):

Introduce damos_quota_goal->complement for specifying whether to use a
complemented value of the given goal target metric.  Add the field to
the data structure and implement essential core support.  Handle the
flag in the quota goal commit and current quota goal metric value
retrieval.

[akpm@linux-foundation.org: fix comment tpyo, per Gutierrez]
Link: https://lore.kernel.org/20260929080113.41708-1-sj@kernel.org
Link: https://lore.kernel.org/20260929080113.41708-2-sj@kernel.org
Signed-off-by: SJ Park <sj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Gutierrez Asier <gutierrez.asier@huawei-partners.com>

1 files changed, 2 insertions, 0 deletions

diff --git a/include/linux/damon.h b/include/linux/damon.h
index 6a29dc2ac8db..42234839ce29 100644
--- a/include/linux/damon.h
+++ b/include/linux/damon.h
@@ -169,6 +169,7 @@ enum damos_quota_goal_metric {
 /**
  * struct damos_quota_goal - DAMOS scheme quota auto-tuning goal.
  * @metric:		Metric to be used for representing the goal.
+ * @complement:		Use the complement of the metric.
  * @target_value:	Target value of @metric to achieve with the tuning.
  * @current_value:	Current value of @metric.
  * @nid:		Node id.
@@ -191,6 +192,7 @@ enum damos_quota_goal_metric {
  */
 struct damos_quota_goal {
 	enum damos_quota_goal_metric metric;
+	bool complement;
 	unsigned long target_value;
 	unsigned long current_value;
 	/* metric-dependent fields */