[PATCH 1/4] mm/damon/core: intorduce per-context region priorities histogram buffer

[SeongJae Park <sj@kernel.org>]

Introduce per-context buffer for region priority scores-total size
histogram.  Same to the per-quota one (->histogram of
struct damos_quota), the new buffer is hidden from DAMON API users by
being defined as a private field of DAMON context structure.  It is
dynamically allocated and de-allocated at the beginning and ending of
the execution of the kdamond by kdamond_fn() itself.

[1] commit 0742cadf5e4c ("mm/damon/lru_sort: adjust local variable to dynamic allocation")
[2] https://lore.kernel.org/20240531122320.909060-1-yorha.op@gmail.com

Signed-off-by: SeongJae Park <sj@kernel.org>
---
 include/linux/damon.h | 2 ++
 mm/damon/core.c       | 5 +++++
 2 files changed, 7 insertions(+)

diff --git a/include/linux/damon.h b/include/linux/damon.h
index fcccaa9b9d54..6342d8f9b0fd 100644
--- a/include/linux/damon.h
+++ b/include/linux/damon.h
@@ -661,6 +661,8 @@ struct damon_ctx {
 	unsigned long next_ops_update_sis;
 	/* for waiting until the execution of the kdamond_fn is started */
 	struct completion kdamond_started;
+	/* for scheme quotas prioritization */
+	unsigned long *regions_score_histogram;
 
 /* public: */
 	struct task_struct *kdamond;
diff --git a/mm/damon/core.c b/mm/damon/core.c
index 84d9b0fd8ace..be3d05357667 100644
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -2019,6 +2019,10 @@ static int kdamond_fn(void *data)
 		ctx->ops.init(ctx);
 	if (ctx->callback.before_start && ctx->callback.before_start(ctx))
 		goto done;
+	ctx->regions_score_histogram = kmalloc_array(DAMOS_MAX_SCORE + 1,
+			sizeof(*ctx->regions_score_histogram), GFP_KERNEL);
+	if (!ctx->regions_score_histogram)
+		goto done;
 
 	sz_limit = damon_region_sz_limit(ctx);
 
@@ -2096,6 +2100,7 @@ static int kdamond_fn(void *data)
 		ctx->callback.before_terminate(ctx);
 	if (ctx->ops.cleanup)
 		ctx->ops.cleanup(ctx);
+	kfree(ctx->regions_score_histogram);
 
 	pr_debug("kdamond (%d) finishes\n", current->pid);
 	mutex_lock(&ctx->kdamond_lock);
-- 
2.39.2